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Also inside this issueOpinion | Market News | IEDM | CIPS 2016APEC 2016 | PCIM 2016 | Industry News | SiC Power ModulesPower Electronics Measurement | Website Locator

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CONTENTS

www.power-mag.com Issue 1 2016 Power Electronics Europe

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Editor Achim ScharfTel: +49 (0)892865 9794Fax: +49 (0)892800 132Email: [email protected]

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ISSN 1748-3530

PAGE 9

IEDM

PAGE 13

CIPS 2016

PAGE 14

APEC 2016

PAGE 16

PCIM 2016

PAGE 18

Industry News

PAGE 22

High-Voltage SiC Power Modulesfor 10 – 25 kV ApplicationsThe development of power electronic devices with higher operating voltages (6.5

kV+) has enabled more power to be transmitted for a given current and reduced

the number of switches required to reach those voltage levels in multi-level

converters. Silicon Carbide (SiC) power devices — with their significantly higher

blocking voltages (into the tens of kilovolts), higher switching frequencies, and

higher operating temperatures (200°C) — have had a major impact on the ability

of power electronics engineers to develop power modules that are more

compact, operate at higher voltages, and require less thermal management than

power modules designed with conventional Silicon devices. Brandon Passmore,

Development Engineering Manager, Chad O’Neal, Development Engineer,

Electronics Packaging, Wolfspeed, Research Triangle Park, USA

PAGE 29

Testing Power Electronic Systems EfficientlyWith today’s increased incorporation of power electronics and switching devices in

overall system design, there is a growing need for accurate measurement of both

the power behavior of the applied power electronics and other inter-related

electrical and physical parameters. Clive Davis, Marketing Manager, Test and

Measurement, Yokogawa Europe & Africa

PAGE 33

Website Product Locator

Maximizing CellMonitoring Accuracyand Data IntegrityGrid-connected battery arrays are viable backup andcarry-through power sources; application-specificmeasurement ICs which meet their unique andsophisticated requirements ensure reliable systemperformance. The use of large-scale battery arrays forbackup and carry-through energy storage is gettingincreasing attention, as evidenced by Tesla Motors’recent announcement of their Powerwall system forhomes and offices. The batteries in these systems arecontinually charged from the power-line grid or othersource, and then deliver AC-line power back to theuser via a DC/AC inverter. Yet while advances inbattery chemistry and technology get much of theattention, an equally critical part of a viable battery-based installation is its battery management system(BMS). As power levels increase, a practical, efficient,and safe system is not a trivial design, and so a grid-connected multicell BMS is a complex system. Manyunique problems need to be understood andaddressed, with safety a major concern as well. Asuccessful and viable system design needs a modular,structured, top-down architecture that is supportedfrom bottom up by optimized components such as theLTC6804 or the newer LTC6811. When combined withsophisticated, secure data-acquisition and controlsoftware, the result is a high-performance, reliableBMS that requires minimal operator involvement, andwill function autonomously for years of reliable service,as this applcation-oriented article will demonstrate. Fullarticle on page 25.

Cover supplied by Linear Technology

COVER STORY

PAGE 6

Market NewsPEE looks at the latest Market News and company

developments

p03 Contents.qxp_p03 Contents 04/02/2016 12:24 Page 3

March 20 -24Long Beach Convention Center

Long Beach, California

The Premier Global Eventin Power ElectronicsTM

Visit the APEC 2016 websitefor the latest information:

www.apec-conf.orgwww.apec-conf.org

04_pee_0116.indd 1 04/02/2016 10:19

OPINION 5


In the early 1980’s, the Silicon bipolar transistor was transformedinto the mass production MOSFET. The 1990’s saw the adoption ofthe IGBT, and the 2000’s brought the superjunction MOSFET intovolume. Now, an even more fundamental transition is underway asSilicon is overtaken by the introduction of SiC and GaN highperformance, wide band-gap power products – according to akeynote speaker at APEC and PCIM 2016. The breakthroughperformance of qualified products, with the subsequent applicationbenefits of size and cost, is now fully appreciated by power systemdesigners. As the ‘eco-system’ continues to mature, with newenabling topologies, control ICs and magnetic solutions, thetransition will accelerate and transform the power electronicsindustry. According to market researcher Yole the power GaN marketis expected to explode. The GaN-on-Si epi wafer market is stillopened and many players are strongly competing. GaN-on-Sitechnology is very challenging.To make GaN power electronics a commercial reality, it has to be

cost competitive with Si-based power electronics. For this, GaNgrown on 6” and 8” Si wafers is a must, as these wafer diametersallow to use conventional Si fabrication infrastructure. The growth ofhigh quality GaN on Si is however very challenging, especially whentrying to optimize the trade-off between breakdown voltage, GaNthickness, and current collapse. One of the major problems for GaNpower devices is current-collapse phenomena, where the on-resistance is not recovered quickly after biasing the high-voltagestress. The phenomena become serious as increasing operationtemperature and/or increasing breakdown voltage. This is caused bythe deep-levels that decrease the carriers in the GaN material. Atpresent, mainstream GaN power devices have a lateral structure. Onthe other hand, progress in vertical devices was slower than that forlateral devices because GaN substrates lacked quality for high

voltage applications. However, GaN substrate can become appliedto high breakdown voltage above 1kV, and the vertical devices haverecently attracted additional research attention. The vertical structurehas the advantages of current-collapse-free operation, small chipsize, easy wiring and a high breakdown voltage. These characteristicsare highly suited for high-power applications.Long-term device reliability is critical for successful

commercialization. A number of degradation mechanisms, such asinverse piezoelectric effect, peak electric field and hot electrondamage, have been shown in the past to impact reliability. Amongthem, electrochemical oxidation plays a key role in inducingmacroscopic defects and pits next to the gate electrode after long-term stress in the off-state. With proper passivation and fieldmanagement, very stable devices have been achieved. But the mainissues have been resolved and several companies have beguncommercializing power devices. During the past five years many power GaN devices have been

launched by established companies such as International Rectifier(acquired by Infineon in late 2014), Panasonic, or start-ups such asEPC, GaN Systems, Transphorm and most recently NavitasSemiconductor. Recent 2015 and this year’s conferences focusesmore on power GaN applicatons. A monolithic GaN power IC 400V / 200 W ZVS converter designed at HRL labs is projected to beable to switch at 100 MHz, with 50 times lower parasiticinductances by shrinking length of power loop 2.5 times andreducing distance between inductance canceling currents by 50 x.The GaN-on-insulator power IC is directly attached to a heat sink.The GaN-on-insulator power IC will have lower parasitic CDS and nosubstrate biasing. Interleaving converters will reduce current rippleand allow scaling to higher power. The 100 MHz GaN power ICconverter should weigh 10 x less and consequently cost less thantoday’s 100 kHz converters. Fully-monolithic GaN-on-Si half-bridgeswith integrated reverse-diodes have been designed at FraunhoferInstitute for Applied Solid State Physics (IAF) in Germany. The high-and low-side switches feature an off-state voltage of 600 V, an on-state resistance of 120 mOhm, and a reverse resistance of below150 mOhm at corresponding drain currents of 30 A. This design willbe demonstrated at PCIM. Decreased commutation times requiresmuch reduced inductances inside power modules. French Dtalentsproposes an optimal geometry of strip line layout everywhere insidethe power module. Return conductors are made of copper foilsmounted face to face in front of chips boundings. Increased widthof conductors, and decreased thickness of insulation, leads to aninductance around only one Nano-Henry. And on the magnetic sidea new ferrite material for GaN Resonant Transformers has beendeveloped at SUMIDA Components & Modules. The rapid progressin GaN power semiconductors will lead to a further miniaturizationof power electronic assemblies and subsystems. Inductivecomponents have a significant impact here. The drastically increasedfrequency requires improved ferrite materials with lowest losses andtransformer designs with unique construction technologies. With agovernmental funded project a new DC/DC resonant convertershould operate up to 3 kVA at frequencies >> 1 MHz.“As Silicon reaches its performance limitations, other new entrants

are delivering significantly greater performance with rapidlydecreasing costs and hundreds of new applications in mainstreammarkets. Independent GaN companies will set the pace whileestablished power Silicon producers will downplay the significanceof the technology”, predicts in his 2016 outlook Alex Lidow, EPC’sCEO. Time will tell whether he is right.More on GaN and other interesting power electronic topics on the

following pages.Achim Scharf

PEE Editor

The Power of GaN

05_PEE_0116.qxp_p05 Opinion 04/02/2016 10:21 Page 5

6 MARKET NEWS

Issue 1 2016 Power Electronics Europe www.power-mag.com

0 million in 2020. “Driven by the SiC-based powerdevices market, the n-type SiC substrates marketwill grow from around $35 million2014 to $110million in 2020, with a 21% CAGR”, expects DrHong Lin, Technology & Market Analyst at Yole. 4”wafers are still preferred for power electronicapplications. However, some suppliers are nowable to provide bigger wafers with good enoughquality for power devices - an 8” SiC wafer wasdemonstrated by II-VI in 2015.

The average price for 6” is still 2.25x higher than4”. However the price continues to decrease andwill drop below the threshold in early 2016. Thetransition to 6” is beginning; in fact, ROHMannounced already mass production on 6” wafers.

The n-type SiC substrate market player rankingshave stabilized of late. Cree remains the marketleader; then follow Dow Corning, SiCrystal (a

ROHM company), and II-VI right behind. Yole analysts identify now four Chinese SiC

suppliers. “Their current announced capacity ismore than 150,000 wafers per year, with furtherincreases expected”, asserted Hong. Moreover, inearly 2015, TankeBlue demonstrated a 6’’ n-typewafer. Thus the Chinese players should beconsidered as serious market challengers.

In parallel, power GaN is expected to explode:The GaN-on-Si epiwafer market is still opened andmany players are strongly competing. GaN-on-Sitechnology is very challenging due to large latticeand the thermal coefficient expansion (CTE)mismatch of between Gallium Nitride and Silicon.That said, GaN-on-Si’s main issues have beenresolved and several companies have beguncommercializing power devices based on thistechnology. Attracted by the device market’s

potential, players with different origins are active on the GaN-on-Si epiwafer open market and thinking of selling epiwafers to deviceplayers.

These players are Silicon substrate supplierswanting to move up the value chain, for exampleSiltronic, device foundries like Episil that want tomove down the value chain, some LED chipsuppliers (for example San’an), large epi housessuch as IQE, Epigan and other pure GaN epihouses. Hong comments: “The power GaN devicebusiness is only in early stages, the related GaNepiwafer open market is not yet well-established.Competition is very intense; Azzurro’s 2014bankruptcy has illustrated the risks faced by start-up GaN epi houses.”

www.yole.fr

WBG Technologies Open The Way To New Markets

EpiGaN, a European supplier of commercial-grade6- and 8-inch GaN-on-Silicon epi-wafers for 600-VHEMT (High Electron Mobility Transistor) powersemiconductors, and SunEdison Semiconductor, amanufacturer of Silicon substrates forsemiconductor manufacturing, have signed aglobal representation agreement for EpiGaN’ epiwafers.

EpiGaN, located in Hasselt, Belgium, offers aportfolio covering power switching applications up

to 650 V as well as RF power devices formillimeter-wave applications. EpiGaN is todaydeveloping and sampling GaN structures on 200mm Si substrates for power switching devices. Akey concept of EpiGaN’s technology base is the in-situ SiN cap layer, which provides high passivationproperties and device reliability. The use of in-situSiN allows the use of pure AlN layers as barriermaterial with the resulting heterostructures havingsheet resistance values below 300 Ohm/sq.

Combining EpiGaN’s technology with SunEdisonSemiconductor’s market presence and expertiseopens a new one-stop solution for IDMs active innext-generation GaN power technology on Sisubstrates. EpiGaN was formed in 2010 as a spin-off of Belgian micro and nano-tech researchorganization imec.

www.epigan.com,www.sunedisonsemi.com

EpiGaN and SunEdison Serve GaN-on-Si Globally

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MARKET NEWS 7


EPC’s CEO Alex Lidow was selected as the recipient of the 2015 SEMI Awardfor North America for the innovation of power device technology, enabling thecommercialization of GaN. Dr. Lidow was honored for his work in the area ofProcess and Technology Integration. Established in 1979, the SEMI Award wasdesigned to recognize significant technological contributions to thesemiconductor industry and to demonstrate the industry’s high esteem for theindividuals or teams responsible for those contributions. Gallium Nitride (GaN) transistors and ICs offer faster and more power-

efficient products compared with those made from Silicon. The use of GaNenables entirely new technologies and the advancement of existingtechnologies in a variety of areas, including 4G and 5G wirelesscommunications, wireless charging, augmented reality glasses, autonomousvehicles and wireless medical technology, to name a few. “Semiconductorsfuel innovation, creating the backbone of technology advancement andsubsequently, the economy at large,” commented Lidow. “It has been mydriving passion to save energy by developing more efficient semiconductors.The team at EPC has delivered first off-the-shelf enhancement-mode GaNtransistors and ICs and will continue to partner with our customers to use GaNto change the way we live.”

www.epc-co.com ¶

KEEP UPWITH THETIMES

II

E-world 2016

Hall 4 / Stand 4-211

Plessey, Anvil Semiconductors and the University of Cambridge (UK) areworking together to fabricate high efficiency LEDs in cubic GaN grown onAnvil’s 3C-SiC / Si substrates. Cubic GaN has the potential to overcome the problems cause in

conventional LEDs by the strong internal electric fields which impair carrierrecombination and contribute to efficiency droop. This is particularly true forgreen LEDs where the internal electric fields are stronger and are believed tocause a rapid reduction in efficiency at green wavelengths known as “thegreen gap”. The availability of cubic GaN from a readily commercializableprocess on large diameter Silicon wafers is as a key enabler for increasing theefficiency of green LEDs and reducing the cost of LED lighting.

Alex Lidow Receives 2015SEMI Award on GaN

Alex Lidow at PEE’s GaN panel discussion PCIM 2015 showing GaN application PCBs

Cubic GaN LEDs


8 MARKET NEWS


The collaboration, which is partly funded by Innovate UK under the £14million Energy Catalyst Program, follows on from work by AnvilSemiconductors and the Cambridge Centre for GaN where they successfullygrew cubic GaN on 3C-SiC on Silicon wafers by MOCVD. The underlying 3C-SiC layers were produced by Anvil using its patented stress relief IP thatenables growth of device quality SiC on 100 mm diameter Silicon wafers. Theprocess is readily migrated onto 150 mm wafers and potentially beyondwithout modification and is therefore suitable for large, industrial-scaleapplications. Plessey have started to commercialize LEDs produced inconventional (hexagonal) GaN grown 150 mm silicon wafers using IPoriginally developed at the University of Cambridge. Anvil’s 3C-SiC on Silicon

technology, which is being developed for SiC power devices, provides aneffective substrate, to allow single phase cubic GaN epitaxy growth andprovides a process which is compatible with Plessey’s GaN on Si devicetechnology. “The properties of Cubic GaN have been explored before, but thechallenges of growing this thermodynamically unstable crystal structure havelimited its development. The high quality of Anvil’s cubic SiC on Si substratesand our experience of developing conventional GaN LED structures on largearea wafers have enabled a breakthrough in material quality”, Prof. ColinHumphreys, Director of the Cambridge Centre for GaN commented.

www.plesseysemiconductors.com, www.anvil-semi.co.uk,

StarPower Europe AG, the Europeansubsidiary of the Chinese powersemiconductor manufacturer StarPowerSemiconductor Ltd., is strengthening itstechnical sales with the powersemiconductor expert Rickmer Heubeck-Wex.Heubeck-Wex has been working within

the power semiconductor market for manyyears, he was previously employed asProduct Manager, Key Account Manager and

Head of National Sales at Semikron for 16years in the division of semiconductormodules and systems. “The recruiting ofadditional personnel for the sales teamwith an experienced power electronicsspecialist is an important step on our pathto expanding the company’s marketpresence in Europe, in order to meet theincreasing demand for qualitysemiconductors in the IGBT and bipolarmodule division,” said Managing Director

Peter Frey. In the past fiscal year, StarPowerachieved a record turnover of $70 millionwith 350 employees. StarPower offersstandard IGBT modules in 600, 1200 and1700 V, as well as MOSFET and bipolarmodules. All common circuits, such as half-bridges, 6 and 7 packs, IPMs, 3 and 5-levelmodules, are produced in various packagesand performance classes.

www.starpowereurope.com

StarPower Strengthens its Sales Team

The global market for semiconductors used inelectric vehicle (EV) charging stations for plug-inhybrid (PH) and battery electric vehicles (BEV) willcontinue to expand in the coming years, providingsignificant growth opportunities to semiconductormanufacturers. Revenue from semiconductors used in EV

charging stations reached $44 million in 2014 andis expected to grow at a compound annual growthrate (CAGR) of 39 percent to reach $233 million

in 2019, according to market researcher IHS. “Fastcharging is a necessary step to the strong adoptionof EVs and a higher power rating is required tosupport these shorter charging times,” said analystNoman Akhtar. “Electric vehicle charging stationswith higher ratings require more powersemiconductors, especially discrete semiconductorcomponents, which will lead to increasedsemiconductor revenue growth.”In 2014, the average price for semiconductor

components in a level-two charging station —which could charge a battery in about five hours— was $143. By comparison, semiconductorcomponents used in the latest fast-chargingdirect-current (DC) chargers now cost more than$1,000; however, they are capable of charging avehicle battery to 80 % of capacity in just 15minutes. Average selling prices ofsemiconductors used in communicationmodules are expected to increase over time, as

the industry moves towardsingle system-on-chip (SoC)solutions that not only providefaster control, but also includethe memory required forsecure communications andother applications. “Bettercommunication between theutility and the charger improvesthe stability of the electric grid,”Akhtar said. “The latestdevelopments incommunication interface ICsenable more secure andreliable information transfer.”

www.ihs.com

Strong Semiconductor Growth Forecast for Electric Vehicle DC Fast-Charging Stations


www.ieee-iedm.org IEDM 9


Power GaN in ResearchThe 61st annual IEEE International Electron Devices Meeting (IEDM) was heldin December 2015 in Washington DC. Back by popular demand for the thirdyear, the 2015 IEDM featured a slate of designated focus sessions on topics ofspecial interest such as Beyond von Neumann Computing, Layered 2DMaterials and Devices, Flexible Hybrid Electronics, Silicon-based Nano-devicesfor Detection of Biomolecules and Cell Function, and Advances in WideBandgap Power Devices – which are our main focus. To make GaN power electronics a commercial reality, it has to be cost

competitive with Si-based power electronics. For this, GaN grown on 6” and 8”Si wafers is a must, as these wafer diameters allow to use conventional Sifabrication infrastructure. The growth of high quality GaN on Si is however verychallenging, especially when trying to optimize the trade-off betweenbreakdown voltage, GaN thickness, and current collapse. Long-term device reliability is critical for successful commercialization. A

number of degradation mechanisms, such as inverse piezoelectric effect, peakelectric field and hot electron damage, have been shown in the past to impactreliability. Among them, electrochemical oxidation plays a key role in inducingmacroscopic defects and pits next to the gate electrode after long-term stressin the off-state. With proper passivation and field management, very stabledevices have been achieved.In spite of the excellent performance of lateral GaN devices, theoretical

considerations indicate that vertical GaN transistors offer the ultimate powerdensity management capability. This is due to a much more uniform heatgeneration, thanks to the vertical current path in these devices. Unfortunately,

New GIT provided with hole-injector at the anode region like IGBT and measured current-collapse behavior with and without anode-injector

SEM cross-section of 0.25 �m gate normally-off GaN FET fabricated with Ge-doped re-growth technique achieving RonWg of 0.95 Ωmm

Normally-off GaN transistor named GIT (Gate Injection Transistor) where AlGaN gate isused to prevent reverse injection

the bulk GaN substrates traditionally used for GaN vertical devices areexpensive and their small diameter precludes the use of state-of-the-art Si fabsfor device fabrication, which further increases the device cost.At US MIT a new generation of vertical GaN devices on Si substrates are

under development to take advantage of the high power density of verticaldevices, at the cost-point of Silicon. One of the main challenges for thesedevices is the high off-state leakage current. The leakage through the GaNsidewall was found to dominate our first generation of GaN vertical diodes.Once that this sidewall was passivated with a novel plasma-based surfacetreatment, vertical GaN power diodes on Silicon were fabricated with betteroff-state leakage current levels than lateral devices. This opens a path towardsthe use of these new vertical devices in commercial applications.

Renovation of Power Devices by GaN-based MaterialsThis was the title of the presentation by Daisuke Ueda from Kyoto Institute ofTechnology in Japan. Si trench MOSFETs have been widely used in the low-voltage applications since the structure enables to reduce on-resistance (Ron)by increasing the gate-width (Wg). Ron is the sum of channel-resistance (Rch)and drift-region-resistance (Rd). Most effective to reduce Ron is scaling-down inthe low-voltage range. For example, a 100 nm GaN FET is sufficient to be usedin typical 12 V DC power-supplies, while Si MOSFET needs 500 nm spacing,thus we can drastically reduce the chip size in designing GaN power IC in thelow-voltage range.Scalability is significant advantage of wide bandgap device. One of the

problems in miniaturizing GaN FET is the increase of contact resistance insource/drain regions. Recently, a new technology was developed to reducethe contact resistance by heavily Ge-doped re-growth. One order of magnitudehigher carrier concentration was obtained in Ge-doped regrowth layer resultingin the significant reduction of contact-resistance.The normally-off GaN transistor named GIT (Gate Injection Transistor) from

Panasonic, where holes are injected from the gate, enable high switching-

speed with conductivity modulation. Though the life-time of the injectedcarrier is thought to be short because of direct recombination and defect-based recombination process inside the GaN material. Short life-time ofminority carrier reduces the effect of conductivity modulation. Experimentallyfabricated GIT shows strong dependency of switching time on the operationcurrent. This phenomenon can be explained by the suppressed recombinationowing to the spatially separated holes and electrons in the drift region due toinherent polarization. One of the major problems for GaN power devices is current-collapse

IEDM.qxp_Layout 1 04/02/2016 10:56 Page 9

10 IEDM www.ieee-iedm.org


phenomena, where Ron is not recovered quickly after biasing the high-voltage stress. The phenomena become serious as increasing operationtemperature and/or increasing breakdown voltage. This is caused by thedeep-levels that decrease the carriers in the GaN material. A recentlydeveloped GIT with p+-anode with IGBT-like structure completelyeliminates the current-collapse due to the trap-filling process by the injectedcarriers. This suggests introducing conductivity modulation is effective infuture vertical GaN power device to widen the applications toward theapplication layer of infrastructure.

Increasing the Switching Frequency of GaN HFET ConvertersThe GaN switches need short gate length to reduce channel resistance, lowgate leakage for reliability, and e-mode for safe operation. D-mode GaN HFETsemploy vertical ~ 30V Si MOSFETs in cascode for effective e-mode switches,but this approach is not suitable for GaN ICs. HRL’s (www.hrl.com) approachfor an e-mode GaN switch is a native insulator, similar to Si02 on Si. The AlN-based gate has low IV hysteresis and gate leakage current of 2 nA/mm at 600V. The channel has a mobility of 1000 cm2/V-s.Faster switching reduces switching loss of converter. Increasing the

frequency an efficient converter requires proportional decreases of parasitic

HRL’s e-mode GaN HFET insulating gate structure illustrating key features

GaN HFET hybrid IC half bridge circuit, with vertical power loop to reduce inductance

overshoot to less than 1 V, however it slowed switching speed. The hard-switched 1MHz boost converter efficiency was 96 %. A monolithic GaN power IC 400 V / 200 W ZVS converter is projected to be

able to switch at 100 MHz, with 50 times lower parasitic inductances byshrinking length of power loop 2.5 times and reducing distance betweeninductance canceling currents by 50 x. The GaN-on-insulator power IC isdirectly attached to a heat sink. The GaN-on-insulator power IC will have lowerparasitic CDS and no substrate biasing. Interleaving converters will reducecurrent ripple and allow scaling to higher power. The 100 MHz GaN power ICconverter should weigh 10 x less and consequently cost less than today’s 100kHz converters.

200 mm GaN-on-Si epitaxyDevelopment of GaN-on-Si e-mode technology for high power applicationsrequires high voltage buffers and suitable device architectures to enablenormally-off operation. Furthermore, the thermal and lattice mismatchbetween GaN and Si limit its scalability to larger areas (200mm and beyond).Wafer bow and morphological challenges needs to overcome, as explainedby Denis Marcon from Belgium-based research lab imec (www.imec.be).The continued research on GaN e-mode devices has converged gradually

towards two competing device architectures for e-mode - recessed gateMISHEMT and p-GaN HEMT. Recessed gate MISHEMTs are obtained by fullyrecessing the AlGaN barrier to locally interrupt the 2DEG. Imec performed thefull recess of the barrier as it minimizes non-uniformities over the 200 mmwafer. The challenges related to this architecture are the difficulties to obtaindevices with a Vth above 1.5 V combined with on-resistance below 10Ω·mm, and low PBTI (Positive Bias Thermal Instability). Different gatedielectrics have been tried, such as PEALD Si3N4 or ALD Al2O3. A higher Vth isobtained with an optimized PEALD Si3N4, however with too high hysteresis. Alower hysteresis and a 10 times improvement in terms of PBTI is obtainedwith an optimized ALD Al2O3 however, at the cost of a lower Vth. Furtherunderstanding of the role of bulk and interface charges in/at the gatedielectric are required. Moreover, in high volume Au-free manufacturing, there are few options for

further Vth increase by switching to electrode materials with higher workfunction (e.g. Ni/Au) and the tuning of threshold voltage through charges canresult in Vth instabilities with temperature. Despite the use of an optimizedgate dielectric, the electron mobility in the channel below the fully recessedgate is typically lower than for d-mode and p-GaN HEMTs, thus significantlycontributing to Ron. The p-GaN HEMT has better control over the gate region. The threshold

voltage can be tuned by the thickness and doping of the p-GaN layer and bythe barrier height of the electrode. P-GaN HEMT devices have very lowhysteresis. The first challenge for the p-GaN HEMT device consists ofcontrolling the Mg diffusion from the p-GaN layer into the access region andto avoid Mg deactivation during processing. With an optimization processImec obtained e-mode devices with Vth larger than 2 V, Ron =7 Ω·mm and Idsat

Schematic cross- section (upper part) and TEM of the gate region (lower part) of arecessed gate MISHEMT (left) and a p-GaN HEMT

inductances in power loop and gate drive. To achieve efficient switching at1MHz, HRL employed a hybrid GaN IC on 250�m AlN substrates. The loopsize was reduced by employing bare die, and a vertical current loop to cancelmost of the inductance. Integrated bare Si die gate driver reduces driveresistance to 50 mΩ and gate inductance to <1nH. During the high dV/dt of325 V/ns switching the drain voltage overshoot was 200 V and the gateovershoot was more than 2 V, exceeding the device ratings. Critically dampingthe gate drive turn-on reduced drain overshoot to less than 20 V and gate


www.ieee-iedm.org IEDM 11


at 1 V > 0.4 A/mm. Forward gate leakage could represent a secondchallenge for this approach as it has been often reported to be quite high,thus representing a concern for reliability. However, it could be optimized toobtain less than 10 nA/mm at Vg =+12 V. The main processing challenge forthis approach is the p-GaN etching, and surface restoration and passivation.This process impacts Ron scaling as a function of Lgd and can cause surface-related dispersion phenomena. In-situ MOCVD Si3N4 surface passivation forlow dispersion could be combined with a p-GaN HEMT concept byperforming a selective re-growth of the p-GaN layer in the gate area. Firstoptimization experiments have shown that good quality p-GaN layer could beselectively re-grown, thus opening perspectives for this hybrid architecturethat combines the best of two e-mode concepts.

State-of-the-Art GaN Vertical Power Devices Tetsu Kachi from Toyota Central R&D Labs gave an outlook on thefabrication issues of bulk GaN power transistors. Over the past decade, there are two types of GaN devices being

developed, with either a lateral or a vertical structure. At present,mainstream GaN power devices have a lateral structure. On the other hand,progress in vertical devices was slower than that for lateral devices becauseGaN substrates lacked quality for high voltage applications. However, GaNsubstrate can become applied to high breakdown voltage above 1kV, andthe vertical devices have recently attracted additional research attention. The vertical structure has the advantages of current-collapse-free

operation, small chip size, easy wiring and a high breakdown voltage. Thesecharacteristics are highly suited for high-power applications. The firstdeveloped device at Toyota was normally-on, with a threshold voltage -16V, because the gate channel was an AlGaN/GaN heterostructure. This was

the first demonstration of a vertical GaN transistor on a GaN substrate.Another device structure: a conventional trench MOSFET has also been

examined. ICP dry etching was first used to form the trench. The trenchshape after the dry etching was a V-shaped groove, and the sidewall of thetrench was rough. Wet etching using tetramethylammonium hydride(TMAH) modified the dry-etched sidewall to be atomically flat. A GaNtrench MOSFET was demonstrated using this novel trench fabricationtechnology.The main issue is the quality of the GaN substrate. Toyota evaluated GaN

substrates by forming Schottky barrier diodes on them in the early 2000’sand observed high leakage currents under low reverse voltages. Recently,new approaches to high quality GaN substrates are being developed. Theseare liquid-phase growth technologies - the ammonothermal and the Na fluxmethod. Both substrates contain few screw dislocations, these substrateshave sufficient quality for high voltage applications. However, the entireGaN substrate area does not yet have a uniform quality. The remaininggoals for GaN substrates are larger wafers of uniformly high quality anddislocation reduction.An other issue is low n-type doping control of the epitaxial layers. For

example, a carrier concentration of less than 1�1016 cm-3 is required forbreakdown voltages above 3 kV. However, epitaxial layers grown byMOCVD in general contain carbon atoms from Ga source, trimethylgalliumat concentrations of approximately 1�1016 cm-3. These carbon atoms willcompensate Si donors and reduce electron mobility. The epitaxialconditions have been improved to reduce the carbon inclusion, and theresidual carbon concentration was reduced to 3�1015 cm-3. To obtain the high breakdown voltage for a Schottky barrier diode (SBD),

planarization of the GaN surface was effective. Toyota applied the catalyst-referred etching to planarize the epitaxial surface of GaN.

From Epitaxy to Converters Topologies Developments of AlGaN/GaN based devices are driven by power switchingapplications, according to Lea Di Cioccio from CEA (www.cea.fr) inFrance. To compete in the market with SiC MOSFETs or Si IGBTs,performances of GaN HEMTs are of importance but cost is critical. Thismeans high quality epitaxial layer growth with GaN on 200 mm Siliconsubstrates are the main challenges, while packaging and innovativetopologies are also essential. The design of Ga(Al)N epitaxial layers on Si (200 mm) has not yet

Schematic cross-section (left) and first optimization tests of selective p-GaN re-growth

Fabrication process of the GaN trench - first step after ICP dry etching (left) and wetetching followed by the dry etching

Cross-sectional structure of the GaN trench MOSFET. The trench was formed noveletching technology


12 IEDM www.ieee-iedm.org

cause the low side device to turn on accidentally. This phenomenon willincrease the risk of power shoot- through and must be avoided. Techniquessuch as “the Miller clamp” are already used in industrial gate drivers toaddress this issue.

A demonstrator of a WBG Gate Driver with Normally-On embeddedmanagement, (0.35 �m SOI technology) has been implemented at CEA ona converter test board and tested up to 200°C.

Converter topologies should push the adoption of normally-on HEMTswith dedicated designs to handle the safety operation of the system. Thechannel conductivity of N-on is twice that of N-off HEMT, and thecomponent technology will be easier, with no drastic gate recess, and noneed for a high positive Vth. The cascode topology does not meet the highvoltage requirement as the Si MOSFET is limited by its operating junctiontemperature. The cold start-up could be a solution. AS

Wide Band Gap Gate Driver with Normally-On embedded management implemented with0.35�m SOI technology

Normally-on device motor inverter cold-start up sequence (1-control added for n-ondevices, 2-inverter input capacitor charge, 3-full power)

reached maturity and its impact on the final power device behavior is stillsignificant. Buffer layers are needed to manage both the initial growth onSilicon and to adjust the stress in the layers to control the wafer bow. Byimproving the insulating behavior of these layers a leakage current of 50nA/mm2 at 600 V has been achieved for a total thickness less than 4 �m.Furthermore, the hole defect density has been drastically lowered thusincreasing the blocking voltage limit. As a consequence devices up to 12mm2 can be produced with no impact on the leakage current.

The very fast switching characteristics of GaN introduce a problemcaused by extreme variations in the drain voltage, commonly named dv/dt.High levels of dv/dt cause high current flow due to the Miller capacitancebetween the gate and the drain. It also induces a high common modecapacitive current in many converters architectures. In a half-bridgetopology, a gate driver output stage with a relatively high on-resistance may

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CIPS 2016 13


Special Conference on Power Electronic Packaging and IntegrationCIPS stands for a 3-day Conference on Power Electronics Packaging and Systems,Keynontes- and invited Papers, Dialog in Postersessions and Table Top Exhibition,and around 300 Delegates from March 8 to 10, 2016, in Nuremberg/Germany.In the next decades, power electronic systemdevelopment will be driven by energy savingsystems, intelligent energy management, powerquality, system miniaturization and higher reliability.Monolithic and hybrid system integration willinclude advanced device concepts (including widebandgap devices), dedicated ideas for systemintegration, new ideas on packaging technologiesand the overall integration of actuators/drives(mechatronic integration).Thus CIPS is focussed on some main aspects

such as: Integration with ultra high power density,of hybrid systems and mechatronic systems;systems and components operational behaviorand reliability; basic technologiesfor integrated power electronicssystems as well as upcomingnew important applicationswhich will be presented ininterdisciplinary invited papers.Since 2010, CIPS is a IEEEsponsored conference. Allaccepted papers are avaible inIEEE Xplore.The keynotes will cover: The

Little Box Challenge (initiated byGoogle) by Prof. Kolar and Prof.Hoene; 100 MHz GaN powerconversion by D. Maksimovic,Uni Boulder; Prospects ofadvances in power magnetics byC.R. Sullivan, Dartmouth College;and Review of Integration Trendsin Power Electronics Systemsand Devices by GourabMajumdar, Mitsubishi ElectricCorporation.Invited papers will cover: SiC

components by Peter Friedrichs,Infineon Technologies AG; GaNfor industrial applications byRadoslava Mitova, Schneider-Electric; Design and Materials ofAntiferroelectric Capacitors forHigh Density Power ElectronicApplications by Günter Engel,CeraCap; Photovoltaic Invertersin µ-Scale by Regine Mallwitz,Technische UniversitätBraunschweig; Investigation of apower module with double

sided cooling using a new concept for chipembedding by DI Hannes Stahr, AT&S AG;Challenges in low-voltage high-current applications- fathom the limits in system design by UlfSchwalbe, Technische Universität Ilmenau; 1-MWSolar Power Conditioning System with BoostConverter using all-SiC Power Module by YasuakiFurusho, Fuji Electric; Parasitic inductance hinderingutilization of power devices by Reinhold Bayerer,Infineon Technologies AG; and New Gate DriverSolutions for Modern Power Devices andTopologies by Reinhard Herzer, SEMIKRONElektronik. The dialogue session has become over the

years a very important part of the CIPS conference.It gives the participants and the authors a particularoccasion to discuss and exchange theirexperiences. In order to promote papers presentedat CIPS during the poster session - known asDialogue Session - organizer VDE grant the BestPoster Award. The winner receives a high-valueaward (brass plate on wood), a certificate andmonetary price of 1.000 Euro. A Young EngineerAward is sponsored by ECPE promoting youngengineers with age below 35 presenting papers atthe CIPS conference.

www.cips-conference.de

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14 APEC 2016


Conference for Practising Power Electronics EngineersAPEC’s comprehensive program is according to the organizers remarkably attractive to theacademic researchers, students, educators, industry, government agencies, and general public.The technical presentation papers are selected from a record high 1212 digests submitted from45 countries. The exposition hits its record high participation with 263 exhibitors and 398 booths.The event will take place from March 20 – 24 in Long Beach, USA.

The Professional Educational Seminars,offered by internationally renowned experts,start on Sunday, March 20. Each of the 21three-and-a-half hour educational seminars,selected from 52 submissions, provides an in-depth discussion of important and complexpower electronics topics and combinespractical application with theory. The Plenary Session, on Monday afternoon,

consists of distinguished world-class speakersfrom industry and academia covering the keypower electronics technologies, components,and innovations affecting our industry and thesociety. Presentations include: The Challenges

of VHF Power Conversion by Tony Sagneri,Finsix Corp.; The Future of Power ElectronicDesign by Michael Harrison, Enphase Energy;Breaking Speed Limits with GaN Power ICs byDan Kinzer, Navitas Semiconductor; ResidentialNanogrids With Battery Storage – Is This OurFuture? by Antonio Ginart, University ofGeorgia; The Future of Magnetic Design forPower Electronics by Ray Ridley, RidleyEngineering; and Why Do Power Supplies Fail?– A Real-World Analysis by David Hill, PowerClinic.The progressively popular industry sessions

feature 119 presentations in 20 sessions from

March 22 – 24.. Speakers are invited to make apresentation only, without submitting a formalmanuscript for the APEC Proceedings. Thisallows to present information on current topicsin power electronics from sources that wouldnot otherwise be present at an industryconference. While many of these sessions aretechnical in nature, some also target business-oriented people such as purchasing agents,electronic system designers, regulatoryengineers, and other people who support thepower electronics industry.

www.apec-conf.org

APEC_2016.qxp_Layout 1 04/02/2016 10:22 Page 14

APEC 2016 15


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Over 240 speakers from more than 25 countries presented the latesttechnological trends in power electronics components and systems at thePCIM Europe 2015 Conference. And this conference with more than 700delegates was backed at the exhibition floor by 417 exhibitors and 88represented companies and nearly 9000 visitors. According to the organizerMesago, the number of exhibitors, as well as the booked exhibition area, arethis year clearly exceeding from May 10 – 12 the previous year’s level. Thisemphasizes the great importance of the event as the leading Europeanknowledge platform within the power electronics community.

Keynotes on current issuesWelcome to the Post-Silicon World: Wide Band Gap Powers Ahead - that isthe title of Dan Kinzer’s PCIM keynote on the first day. He is co-founder of

Navitas Semiconductor, a young company focused on advanced GaN power semiconductor devices and circuits, located in El Segundo, USA. “In the early 1980’s, industry pioneers transformed the Silicon bipolar

transistor into the mass production MOSFET. The 1990’s saw the adoption ofIGBTs, and the 2000’s brought superjunction MOSFET into volume. Now, aneven more fundamental transition is underway as Silicon is overtaken by theintroduction of SiC and GaN high performance, wide band-gap powerproducts. The breakthrough performance of qualified products, with thesubsequent application benefits of size and cost, is now fully appreciated bypower system designers. As the ‘eco-system’ continues to mature, with newenabling topologies, control ICs and magnetic solutions, the transition willaccelerate and transform the power industry”. In his presentation examples will

16 PCIM 2016 www.pcim-europe.com


Bigger Than Ever

Again it’s time to prepare for PCIMEurope Nuremberg in May

PCIM.qxp_Layout 1 04/02/2016 10:31 Page 16

www.pcim-europe.com PCIM 2016 17

be taken from applications such as electric vehicles, renewable energy, powersupplies, and battery chargers.Smart Transformers – Concepts/Challenges/Applications – will be discussed

on the second day keynote by Prof. Dr. Johann Walter Kolar, ETH Zurich PowerElectronic Systems Laboratory. And on the third day the keynote is entitled “Trends of solar system

integration electricity networks” to be given by Jens Merten, Commissariat àl’énergie atomique et aux énergies alternatives, Le Bourget-du-Lac, France.“With their constant cost reduction, solar systems have become already todayan economically viable alternative in many regions of the world. While the costfor solar modules has been drastically reduced in the last years, the costreduction potential for the balance of system, like for example powerconditioners, still needs to be exploited. On the other side, the massivepenetration of variable solar energy systems challenges the management ofthe electricity networks”. His speech outlines trends for solving these issues.

GaN on the system levelSince Gallium Nitride devices have been covered over the past in variousPCIM Special Sessions i. e. organized by PEE this year’s focus within theconference is more on the system level, expressed by a session called “GaNConverters” on the second day.An “EMI Study in a GaN HEMT Power Module” will be presented by

Xiaoshan Liu from SATIE Laboratory in France. The inherent RLC parasitics ofan insulated metal substrate (IMS) power module have been modeled andtheir impacts on EMI have been studied by time domain simulation + FFTanalysis. A PCB IMS has been proposed for a medium power GaN module byusing a 650V 30A e-GaN HEMT. The mid-point parasitic capacitor has beenminimized. IMS parasitic capacitances and discrete SMD capacitors are usedas common mode (CM) and differential mode (DM) integrated filters. The DCbus impedances are balanced to avoid EMI noise transfer from DM to CM. “Ultra-High Frequent Switching with GaN-Fets using the Coss-Capacitances

as non-dissipative Snubbers” is the subject of the second paper by LuisAlfonso Fernández-Serante from FH JOANNEUM in Austria. Due to the fastertransients of wide bandgap transistors, the output capacitance can essentiallyinfluence the switching behavior and the losses. The switching cycle of a 650V GaN-Fet half-bridge is analyzed. A linearized model serves for deriving therelations and explaining how the Coss can be used for minimizing the losses,by using it as an non-dissipative snubber, providing soft switching. EMI-measurements are showing the reduction of radiated emissions when usingsoft-switching mode.An “eGaN FET based 6.78 MHz Differential-Mode ZVS Class D A4WP Class

4 Wireless Power Amplifier” will be introduced by Michael de Rooij, EfficientPower Conversion (EPC) Corporation, USA. An eGaN FETs based 33 Wcapable A4WP class 4 power amplifier is presented. As the power levels andcharge surface area increase, so do the design challenges. This paper delvesinto the challenges to realize a class 4 wireless power solution that includeamplifier thermals, radiated EMI, coil re-tuning, and device side rectification.A “High Frequency, High Temperature DC/DC Converter for GaN Gate

Drivers” has been designed by Yohan Wanderoild at CEA Leti, Grenoble,France. It will be discussed in detail.Finally, a “Fully-Monolithic GaN-on-Si Half-Bridge with Integrated Reverse-

Diodes” will be discussed by Richard Reiner, Fraunhofer Institute for AppliedSolid State Physics (IAF) in Freiburg, Germany. This work presents the design,realization, and the characterization of a monolithic GaN on Si half-bridgecircuit with integrated Schottky-contacts as reverse-diodes. The extrinsic andintrinsic layouts are realized, explained and compared to other approaches.The high- and low-side switches feature an off-state voltage of 600 V, an on-state resistance of 120 mΩ, and a reverse resistance of below 150 mΩ atcorresponding drain currents of 30 A.More GaN demos will be presented within the poster sessions, at the

exhibition floor and in our upcoming extensive PCIM preview, as well as otherpower electronic innovations. AS

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18 INDUSTRY NEWS


The new devices incorporate a constant power output profile which, whenpaired with an adaptive-voltage protocol such as Qualcomm® Quick Charge™3.0 or USB-PD, permits smart mobile device makers to optimize charging timeacross a range of products. Adaptive charging achieve faster charge times,improved charging efficiency and backward compatibility with the popular 5 VUSB BC 1.2 specification, all while minimizing overall thermal managementand battery charging system cost.

Operation principleThe InnoSwitch-CP combines a high-voltage power MOSFET switch, along withboth primary- and secondary-side controllers in one device. It has a novelinductive coupling feedback scheme using the package leadframe and bondwires for accurate direct sensing of the output voltage and output current onthe secondary to communicate information to the primary IC. This so-calledFluxLink™ technology enables secondary-side control with the simplicity andlow component count usually associated with primary-side regulation. FluxLinkalso optimizes the effectiveness of output synchronous rectification, resultingin high efficiency across the full load range. For example, no-load consumptionat 230 VAC is less than 10 mW, while full-load efficiency exceeds 90 %.The IC operate in the current limit mode. When enabled, the oscillator turns

the 650 V synchronous power MOSFET on at the beginning of each cycle. TheMOSFET is turned off when the current ramps up to the current limit or whenthe DCMAX limit is reached. Since the highest current limit level and frequencyare constant, the power delivered to the load is proportional to the primary

New InnoSwitch-CP ICs ImproveCharging Performance of SmartMobile Devices

inductance of the transformer and peak primary current squared. Hence,designing the supply involves calculating the primary inductance of thetransformer for the maximum output power required. If the InnoSwitch-CP isappropriately chosen for the power level, the current in the calculatedinductance will ramp up to current limit before the DC MAX limit is reached.InnoSwitch-CP senses the output voltage on the FEEDBACK pin using a

resistive voltage divider to determine whether or not to proceed with the nextswitching cycle. The sequence of cycles is used to determine the current limit.Once a cycle is started, it always completes the cycle. This operation results ina power supply in which the output voltage ripple is determined by the outputcapacitor, and the amount of energy per switch cycle.Unlike conventional PWM (pulse width modulated) controllers, it uses a

simple ON/OFF control to regulate the output voltage and current. The primarycontroller consists of an oscillator, a receiver circuit magnetically coupled to thesecondary controller, current limit state machine, 5.95 V regulator, over-voltage

Power Integrations announced its InnoSwitch™-CP family of off-line CV/CC flyback switching ICs, asuccessor of the recently introduced Innoswitch-EP. Two devices are available: The INN2214K ICdelivers 15 W constant output power between 5 and 9 V for universal voltage chargers and adapters,while the larger INN2215K part delivers up to 22 W for similar applications. Devices are priced at$0.90 in 10,000-piece quantities.

InnoSwitch™-CP off-line CV/CC flyback switching IC for output power up to 22 W

circuit, current limit selection circuitry, over-temperature protection, leadingedge blanking and a 650 V power MOSFET. The secondary controller consistsof a transmitter circuit that is magnetically coupled to the primary receiver,constant voltage (CV) and constant current (CC) control circuitry, a 4.4 Vregulator, synchronous rectifier MOSFET driver, frequency jitter oscillator and ahost of integrated protection features.The internal clock of the InnoSwitch-CP runs all the time. At the beginning

of each clock cycle, the voltage comparator on the FEEDBACK pin decideswhether or not to implement a switch cycle, and based on the sequence ofsamples over multiple cycles, it determines the appropriate current limit. Athigh loads, the state machine sets the current limit to its highest value. Atlighter loads, the state machine sets the current limit to reduced values. At

Innoswitch-CP primary side controller block diagram

Industry News.qxp_Layout 1 04/02/2016 11:22 Page 18

INDUSTRY NEWS 19


near maximum load, InnoSwitch-CP will conduct during nearly all of its clockcycles. At slightly lower load, it will “skip” additional cycles in order to maintainvoltage regulation at the power supply output. At medium loads, cycles will beskipped and the current limit will be reduced. At very light loads, the currentlimit will be reduced even further. Only a small percentage of cycles will occurto satisfy the power consumption of the power supply.The response time of the ON/OFF control scheme is very fast compared to

PWM control. This provides accurate regulation and excellent transientresponse.

Power supply design considerationsInnoSwitch-CP features a primary sensed OV protection feature that can beused to latch off the power supply. Once the power supply is latched off, it canbe reset if the V pin current is reduced to zero. Once the power supply islatched off, even after input supply is turned off, it can take considerableamount of time to reset the internal controller as the energy stored in the DCBUS will continue to provide bias supply to the controller. A fast AC reset can be achieved using a modified shown circuit

configuration. The voltage across capacitor CS reduces rapidly after input supplyis disconnected which rapidly reduces current into the INPUT VOLTAGEMONITOR pin of the IC and resets the controller.It is recommended that the highest voltage at the output of the bias

winding should be measured for normal steady-state conditions at full ratedload and lowest rated input voltage and also under transient load conditions. AZener diode rated for 1.25 times this measured voltage will typically ensurethat OVP protection will not operate under any normal operating conditionsand will only operate in case of a fault condition. Use of the primary sensedOVP protection is highly recommended.Although a simple diode rectifier and filter is adequate for the secondary-

winding, use of a SR MOSFET enables significant improvement in operatingefficiency often required to meet the European CoC and the U.S. DoE energyefficiency requirements.


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Innoswitch-CP secondary side controller block diagram

Fast AC reset configuration


20 INDUSTRY NEWS


The secondary-side controller turns on the SR MOSFET once the flybackcycle begins. The SR MOSFET gate should be tied directly to theSYNCHRONOUS RECTIFIER DRIVE pin of the InnoSwitch-CP IC. The SRMOSFET is turned off once the drain voltage of the SR MOSFET drops below -24 mV (VSR(TH)). Therefore the use of MOSFETs with a very small on-resistancecan be counterproductive as it reduces the MOSFET’s on-time, commutating

the current to the body diode of the MOSFET or an external parallel Schottkydiode if used.A MOSFET with 18 mΩ RDS(ON) is a good choice for designs rated for a 5

V, 2 A output. The SR MOSFET driver uses the secondary SECONDARY BYPASSpin for its supply rail and this voltage is typically 4.4 V. A MOSFET with too higha threshold voltage is therefore not suitable and MOSFETs with a low thresholdvoltage of 1.5 V to 2.5 V are ideal although MOSFETs with a threshold voltage(absolute maximum) as high as 4 V may be used.Regarding the output capacitor, low ESR aluminum electrolytic capacitors are

suitable for use with most high frequency flyback switching power suppliesthough the use of aluminum-polymer solid capacitors have gainedconsiderable popularity due to their compact size, stable temperaturecharacteristics, extremely low ESR and simultaneously high RMS ripple currentrating. These capacitors enable design of compact chargers and adapters.Typically, 200 µF to 300 µF of aluminum-polymer capacitance is often

adequate for every ampere of output current. The other factor that influenceschoice of the capacitance is the output ripple. Care should be taken to ensurethat capacitors with a voltage rating higher than the highest output voltage withsufficient margin (>20 %) be used.

Typical adapter/charger applicationThe circuit shown in the application schematic is a low-cost high-efficiencyquick charge adapter using the INN2215K. This design features DOE Level 6and EC CoC 5 compliance. The integration offered by InnoSwitch-CP reducescomponent count from >60 to only 41. The charger provides 5 V at 3 A, 9 Vat 2 A and 12 V at 1.5 A. The output is continuously adjustable in 200 mVincrements per the QC 3.0 protocol to set the output voltage to other values.Bridge rectifier BR1 rectifies the AC input supply. Capacitors C1, C2 and C3

provide filtering of the rectified AC input and together with inductor L2 form api-filter to attenuate differential mode EMI. Inductor L1 and capacitor C8provide common mode noise filtering. Capacitor C15 connected at the power

Innoswitch-CP operation at full load (upper left) to very light load (lower right)

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supply output helps to reduce high frequency radiated EMI. Thermistor RT1limits the inrush current when the power supply is connected to the input ACsupply. Input fuse F1 provides protection against excess input current resultingfrom catastrophic failure of any of the components in the power supply.

One end of the transformer primary is connected to the rectified DC bus;the other is connected to the drain terminal of the MOSFET inside theInnoSwitch-CP IC (U1). A low-cost RCD clamp formed by diode D1, resistorsR1, R2 and R3, and capacitor C4 limits the peak drain voltage of U1 at theinstant of turn-off of the MOSFET inside U1. The clamp helps to dissipate theenergy stored in the leakage reactance of transformer T1.

The InnoSwitch-CP IC is self-starting, using an internal high-voltage currentsource to charge the BPP pin capacitor (C7) when AC is first applied. Duringnormal operation the primary-side block is powered from an auxiliary windingon the transformer T1. Output of the auxiliary (or bias) winding is rectifiedusing diode D2 and filtered using capacitor C6. Resistor R4 limits current beingsupplied to the BPP pin of the InnoSwitch-CP IC (U1).

QC 3.0 compliant charger/adapter featuring 5 V, 3 A; 9 V, 2 A; 12 V,1.5 A output

Output regulation is achieved using On/Off control and thenumber enabled switching cycles are adjusted based on theoutput load, as outlined above. There are four operatingstates (current limits) arranged such that the frequencycontent of the primary current switching pattern remains outof the audible range until at light load where the transformerflux density and therefore audible noise generation is at avery low level. The secondary-side of the InnoSwitch-CP ICprovides output voltage, output current sensing and drive tothe MOSFET providing synchronous rectification.

The secondary of the transformer is rectified by diode D3and filtered by capacitors C10 and C11. High frequency

ringing during switching transients that would otherwise create radiated EMI isreduced via a snubber (resistor R8 and capacitor C9). To reduce dissipation inthe diode D3, synchronous rectification (SR) is provided by MOSFET Q1. Thegate of Q1 is turned on by secondary-side controller inside the IC based onthe winding voltage sensed via resistor R7 and fed into the FWD pin of the IC.In continuous conduction mode of operation, the MOSFET is turned off justprior to the secondary-side commanding a new switching cycle from theprimary. In discontinuous mode of operation, the power MOSFET is turned offwhen the voltage drop across the MOSFET falls below a threshold ofapproximately -24 mV. Secondary side control of the primary-side powerMOSFET avoids possibility of cross conduction of the two MOSFETs andprovides extremely reliable synchronous rectification. As the SR MOSFET is noton for the full switching cycle, a small low current diode is still required (D3)to increase efficiency.

www.power.com/innoswitch-cp/


22 SIC POWER MODULES www.wolfspeed.com


High-Voltage SiC PowerModules for 10 – 25 kVApplicationsThe development of power electronic devices with higher operating voltages (6.5 kV+) has enabled morepower to be transmitted for a given current and reduced the number of switches required to reach thosevoltage levels in multi-level converters. Silicon Carbide (SiC) power devices — with their significantly higherblocking voltages (into the tens of kilovolts), higher switching frequencies, and higher operatingtemperatures (200°C) — have had a major impact on the ability of power electronics engineers to developpower modules that are more compact, operate at higher voltages, and require less thermal managementthan power modules designed with conventional Silicon devices. Brandon Passmore, DevelopmentEngineering Manager, Chad O’Neal, Development Engineer, Electronics Packaging, Wolfspeed,Research Triangle Park, USA

Designing and manufacturing thesenew compact, SiC-based high voltagepower modules requires importantconsideration regarding insulation materials,creepage/clearance design, an optimizedparasitic design, external bussing connectionscheme, and high temperature andenvironmental testing. The two SiC powermodules described in this article clearlydemonstrate the potential for SiC devices inhigh-voltage applications, including energystorage, grid-connected power electronics,electric rail, and shipboard power systems.

SiC power module for 15 kVapplicationsA low profile power module has beendesigned around the latest generation ofhigh-voltage SiC device technology, enablingincreased operating voltage whileminimizing both the module’s size and theneed for extensive thermal management.Compared to 6.5 kV Si-based solutions, thisSiC-based power module is one-third thevolume and half the weight, and has 10Xhigher switching speeds and 2X thebreakdown voltage with reduced coolingrequirements. At the system level, thistranslates into more than 10 % increasedefficiency with a 50 % reduction in energylosses, which increases the power density ofthe system. As such, this novel SiC powermodule represents a powerful new buildingblock for power electronics systems thatrequire simplified design and increasedoperating efficiency. Shown in Figure 1, this power module is

a half-bridge configuration with eight SiCpower devices per switch position: four SiC

switching power devices and four SiCSchottky diodes. This module design canemploy a wide range of different high-voltage devices, including SiC MOSFETsrated for 10 kV / 40 A or SiC IGBTs rated for15 kV / 80 A. The module design alsoincludes an integrated temperature sensorthat monitors the die junction temperatureduring operation. Internal bonding variations within the

module include a standard wire-bond dieinterconnect, as well as an option for flip-chip mounting. The substrates, baseplates,and housing are standard for both moduleconfigurations to standardizemanufacturability. After the baseplate and

substrate are joined with high-temperaturesolder, the four separate half-bridgesubassemblies are tested beforeincorporating them into the module. Thisenables separate testing and quality controlfor the subassemblies, providing designengineers with a critical opportunity torework the device prior to final assembly.Subdividing the module’s switch

positions also improves the thermal-mechanical characteristics, reducing theeffects of bowing due to thermal expansionmismatches in the materials used. Thesubassembly baseplates are made from alow coefficient of thermal expansion (CTE)metal-matrix composite material with a low

Figure 1: 15 kV SiC power module rated at 200°C operation - key characteristics include reworkability,modularity, and small form factor

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www.wolfspeed.com SIC POWER MODULES 23


density, which contributes to the 80 %weight reduction, as the baseplate is oftenthe heaviest component of the module.Moreover, since there are typically multiplemodules per system, this module weightreduction can contribute to a significantreduction of the total system weight.

The module housing is molded from ahigh temperature plastic, which providesprotection from higher temperatureenvironments and allows for high-temperature operation. In addition, the hightemperature plastic housing was designed tomeet UL and IEC creepage (Pollution Degree2) requirements based on 15 kV operation.Internal clearances are maintained with ahigh temperature Silicone gel.

To demonstrate the high performancepackaging design coupled with the superiordynamic characteristics of 10 kV SiCMOSFETs, the improvement in dynamiccharacteristics for a submodule can be seenin Figure 2, which illustrates the clampedinductive load test results for the module at8 kV /28 A. Using a gate resistor of 2.5 Ω,the submodule exhibits switching speedsup to 111 kV/µs, which equates to a 10Ximprovement in switching speed overconventional Si IGBTs. The switching energyplots, shown in Figure 3, demonstrate theturn-on, turn-off, and total energy data forthe submodule.

Power Module at 24 kV / 30 A usingSiC IGBTsAn evaluation module using high-voltage(24 kV) SiC IGBTs was recently developedunder a contract with the U.S. ArmyResearch Lab (Cooperative AgreementNumber W911NF-13-2-0023) to meet aspecific requirement for an ultra-highvoltage module with a compact footprint.The internals of the module were designedto withstand 24 kV operation and areshown in Figure 4. As designed, theterminal spacings do not meet clearancespacings to withstand breakdown in openair. Thus, the module was designed tooperate in a dielectric fluid.

The module can be internally configured

for several different basic topologies,including an IGBT diode co-pack, boostchopper, or half-bridge configuration,providing design engineers with severalbuilding block topology choices forimplementing this type of module into abroad range of high-voltage applications.

The module is specifically designed forhigh temperature (200°C) operation,employing dielectric potting material in theinterior of the module and high temperatureplastic for the external housing. The powermodule was carefully designed using finiteelement modeling and advanced CAD toolsto determine mechanical stresses, thermalgradients, electric field strengths, and overall

module parasitics. Additionally, thebaseplate material was selected to have aclosely matched coefficient of thermalexpansion with the thick ceramic substrateused to electrically isolate the high voltageSiC IGBTs from the baseplate.

In previous work performed byWolfspeed [1], the electrical performance ofthe module for reverse blocking andswitching performance over temperature ispresented in Figure 5. The clampedinductive load testing was performed at 14kV / 22 A, demonstrating a switching speedof 46 kV/µs, with some degradation notedas the temperature rises to 125°C.However, it is worth noting that this device

Figure 2: Clampedinductive load

switching waveform(Vbus = 8 kV, Iswitch = 28A, Rg = 2.5Ω) for a

submodule of the 15kV power module

Figure 3: Switchingenergy as a functionof current at 8 kV fora submodule - totalswitching losses are70X lower than a Si-based 6.5 kV / 250 AIGBT power module

Figure 4: 24 kV / 30 ASiC IGBT power

module


24 SIC POWER MODULES www.wolfspeed.com


and its performance will improvesubstantially as development progresses.Overall, the 24 kV SiC IGBTs exhibitextremely fast switching speeds.

ConclusionsThe two high voltage, high temperature SiCpower modules demonstrate the extremelyfast switching characteristics of high voltageSiC-based transistors. Module packagingdesigned especially for these and otherwide bandgap power devices enablesreduced physical size and complexity inmulti-level systems, the elimination of

external cooling systems, and a significantincrease in both efficiency and powerdensity at the system level. Specifically, thehigh voltage and thermal characteristics ofSiC power devices will enable powerelectronics design engineers to significantlyreduce the number of topology levelscompared to conventional silicon powermodules. Although the cost of the SiCdevices is often seen as a barrier toadoption, their cost is continually beingreduced as production volume increases.Furthermore, since the integration of SiCdevices enables a reduction of overall

system cost and significantly increasesperformance, it will not be necessary for SiCdevices to reach true cost parity with Siliconin order to make the overall valueproposition for system integrators successful.

Literature[1] E. V. Brunt, L. Cheng, M.

O’Loughlin, C. Capell, C. Jonas, K. Lam,et al., “22 kV, 1 cm2, 4H-SiC n-IGBTs withImproved Conductivity Modulation,” in26th International Symposium on PowerSemiconductor Devices & IC’s, Waikoloa,Hawaii, 2014, pp. 358-361.

Figure 5: Reverse leakage for 24kV SiC IGBTs (left) and dynamic characteristics for 24 kV / 30 A SiC IGBTs over temperature

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Maximizing Cell MonitoringAccuracy and Data IntegrityGrid-connected battery arrays are viable backup and carry-through power sources; application-specificmeasurement ICs which meet their unique and sophisticated requirements ensure reliable systemperformance. Mike Kultgen, Greg Zimmer, Linear Technology, and Stefan Janhunen, BMSProducts, Nuvation Engineering, USA

The use of large-scale battery arrays forbackup and carry-through energy storage isgetting increasing attention, as evidencedby Tesla Motors’ recent announcement oftheir Powerwall system for homes andoffices. The batteries in these systems arecontinually charged from the power-linegrid or other source, and then deliver AC-line power back to the user via a DC/ACinverter.

Using batteries for power backup is notnew, with many systems spanning basic120/240V AC and several hundred wattsfor short-term desktop-PC backup, tothousands of watts for specialty vehicles,such as ships, hybrid cars, or all-electricvehicles, up to hundreds of kilowatts forgrid-scale telecom and data-center backup.Yet while advances in battery chemistryand technology get much of the attention,an equally critical part of a viable battery-based installation is its batterymanagement system (BMS).

There are many challenges whenimplementing battery managementsystems for energy storage, and theirsolutions do not simply “scale up” fromsmall-scale, lower-capacity battery packs.Instead, new and more sophisticatedstrategies and critical support componentsare needed.

The challenge begins with the need forhigh accuracy and confidence in the manymeasurements of key battery cellparameters. Further, the design must bemodular in its subsystems to enabletailoring the configuration to the specificneeds of the application, along withpossible expansion, overall managementissues, and necessary maintenance.

The operating environment of larger-scale storage arrays brings other significantchallenges, as well. The BMS must provideprecise, consistent data within anextremely noisy electrical and often hotenvironment despite the highvoltage/current inverters and resultantcurrent spikes. In addition, it must provideextensive “fine-grain” data on internalmodule and system temperature

measurements, which are critical forcharging, monitoring, and discharging,rather than just a few broad-brushaggregate values.

Due to the basic role of these powersystems, their operating reliability isinherently critical. To translate that easilystated objective into reality, the BMS mustensure data accuracy and integrity, alongwith continuous health assessments so itcan take the needed actions on anongoing basis. Achieving a robust designand safety is a multi-level process, and theBMS must anticipate problems, performself-test, and provide failure detection onall subsystems, then implementappropriate actions while in standby andoperational modes. As a final mandate,due to the high voltage, current, andpower levels, there are many stringentregulatory standards that the BMS mustmeet.

System design translates concepts tothe real-world resultsAlthough monitoring rechargeable batteriesis simple in concept – just place thevoltage- and current-measurement circuitsat the cell terminals – the reality of a BMSis quite different and much morecomplicated.

Robust design begins withcomprehensive monitoring of individualbattery cells, which places significantdemands on analog functions. The cellreadings need millivolt and milliampaccuracy, and voltage and currentmeasurements must be time-synchronizedto calculate power. The BMS must alsoassess validity of each measurement, as itneeds to maximize data integrity, while itmust also identify errors or questionablereadings. It cannot ignore unusual readingswhich may indicate a potential problem,but at the same time, it should not takeaction based on data which has errors.

A modular BMS architecture enhancesrobustness, scalability, and reliability.Modularity also facilitates use of isolationwhere needed in the data links between

subsections to minimize impact ofelectrical noise and to enhance safety. Inaddition, advanced data-encoding formatsincluding CRC (cyclic redundancy check)error detection and link-acknowledgementprotocols assure data integrity, so thesystem management function hasconfidence that the data it receives is whatwas sent.

An example of a BMS that incorporatesthese principles is the scalable andcustomizable battery management systemdeveloped by Nuvation Engineering. ThisBMS design is proving itself with designwins in grid energy-storage systems andpower-backup equipment, where reliabilityand ruggedness are critical. The keyadvantage for this off-the-shelf BMS is itstiered, hierarchical topology (Figure 1) withthree subsystems, each with uniquefunctions, as shown in Figure 2.

The cell interface provides tightmanagement and monitoring of eachbattery cell in a stack; the system uses asmany cell interfaces as needed, dependingon the number of stacks. These interfacescan be daisy-chained as the number ofcells and thus the stack voltage increases.The cell interface is connected to a singlestack controller which monitors andmanages multiple cell-interface units.Multiple stack controllers can be connectedtogether, if needed, to support large packswith many stacks in parallel. The powerinterface connects the stack controllers tohigh voltage/current lines and is theinterface to the inverter/charger. It isolateshigh-voltage and high-current componentsof the stack physically and electrically fromthe other modules. It also powers the BMSdirectly from the battery stack, thuseliminating the need for any externalpower supplies for the BMS operation.

The modular and hierarchicalarchitecture of the Nuvation BMS supportsbattery-pack voltages ranging up to 1250VDC, using cell-interface modules eachcontaining up to 16 cells, stacks with up to48 cell-interface modules, and batterypacks that contain multiple stacks in

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26 BATTERY MANAGEMENT www.linear.com, www.nuvation.com


parallel. The entire array assembly ismanaged as a single unit from the user’sperspective.

Solid design also builds from thebottom upFactors such as modular architecture,hierarchical topology, and error-awaredesign are essential to the integrity andexpandability of the Nuvation BMS, but notenough. A successful implementationrequires high-performance functionalblocks to serve as the physical foundation. That’s why the LTC6804 Multicell Battery

Monitor IC (Figure 3) plays a critical role inthe Nuvation BMS implementation. It isexpressly tailored for the needs of BMSsystems and multicell designs, beginningwith providing precise measurements onup to 12 battery cells stacked in series. Itsmeasurement inputs are not ground-referenced, which greatly simplifiesmeasurement of those cells, and the

LTC6804 itself is stackable for use withhigher-voltage arrays (and it also supportsa variety of cell chemistries). It offersmaximum 0.033 % error with 16-bitresolution, and needs just 290 ?s tomeasure all 12 cells in the stack. Suchsynchronized voltage and currentmeasurements are critical to yieldmeaningful analysis of power parameters. Of course, performance in the benign

environment of a prototype at the bench isnot the same as actual achievableperformance in an electrically andenvironmentally hostile real-world BMSsetting. The LTC6804’s analog/digitalconverter (ADC) architecture is designedto resist and minimize those detrimentaleffects, using filters specifically designedfor the noise of power inverters. The data interface uses a single twisted-

pair, isolated SPI interface which supportsrates up to 1 Mb and distances of up to100 m. To further enhance system

integrity, the IC Includes an array ofongoing subsystem tests. As furtherindication of its reliability and ruggedness,the LTC6804 meets the stringent AEC-Q100 standard for automotive quality. ThisIC achieves its results due to anapplication-specific design which focusesclosely on BMS issues and environments,including the unique system-levelobjectives of the application and its manychallenges.

Three major issues resolvedThe LTC6804 addresses three majorareas which affect system performance,conversion accuracy, cell balancing, andconnectivity/data-integrityconsiderations:1) Conversion accuracy: Due to theshort- and long-term accuracy demands ofthe BMS application, it uses a buried-Zenerconversion reference rather than abandgap reference. This provides a stable,

LEFT Figure 1: TheNuvation Engineeringbattery managementsystem is theinterface between theAC power grid and anarray of battery cells;it provides bothsophisticated batterycharging/dischargeoversight as well asthe DC/AC inverterfunction

Figure 2: The three major subsystems of the Nuvation BMS - cell interface,stack controller, power interface - comprise a modular, hierarchical designwhich results in scalability, robustness, and reliability across a wide rangeof power levels as shown in the block diagram (above) and physicalrealization (right)


www.linear.com, www.nuvation.com BATTERY MANAGEMENT 27


low-drift (20 ppm/√kHr), low-temperaturecoefficient (3 ppm/K), low-hysteresis (20ppm) primary voltage reference along withexcellent long-term stability. This accuracyand stability is critical since it is the basisfor all subsequent battery-cellmeasurements and these errors have acumulative impact on acquired-datacredibility, algorithm consistency, andsystem performance.

Although a high-accuracy reference is anecessary feature to ensure superiorperformance, that alone is not enough.The A/D converter architecture and itsoperation must meet specifications in anelectrically noisy environment, which is theresult of the pulse-width modulated(PWM) transients of the system’s highcurrent/voltage inverter. Accurateassessment of the state of charge (SOC)and health of the batteries also requirescorrelated voltage, current, andtemperature measurements.

To mitigate the system noise before itcan affect the BMS performance, the

LTC6804 converter uses a delta-sigmatopology, aided by six user-selectable filteroptions to address noisy environments.The delta-sigma approach reduces theeffect of electromagnetic interference(EMI) and other transient noise, by its verynature of using many samples perconversion, with an averaging, filteringfunction. 2) Cell balancing: The need for cellbalancing is an unavoidableconsequence in any system that useslarge battery packs arranged as groups ofcells or modules. Although most lithiumcells are well matched when firstacquired, they lose capacity as they age.The aging process can differ from cell tocell due to a number of factors, such asgradients in pack temperature.Exacerbating the whole process, a cellthat is allowed to operate beyond itsSOC limits will prematurely age and loseadditional capacity. These differences incapacity, combined with small differencesin self-discharge and load currents, lead

to cell imbalance.To remedy the cell imbalance issue, the

LTC6804 directly supports passivebalancing (with a user-settable timer).Passive balancing is a low cost, simplemethod to normalize the SOC for all cellsduring the battery charge cycle. Byremoving charge from the lower capacitycells, passive balancing ensures theselower capacity cells are not overcharged.The LTC6804 can also be used to controlactive balancing, a more-complicatedbalancing technique which transfers chargebetween cells through the charge ordischarge cycle.

Whether done using active or passiveapproaches, cell balancing relies on highmeasurement accuracy. As measurementerror increases, the operating guardbandwhich the system establishes must also beincreased, and therefore the effectivenessof the balancing performance will belimited. Further, as the SOC range is furtherrestricted, the sensitivity to these errorsalso increases. The LTC6804’s totalmeasurement error of less than 1.2 mV iswell within system-level requirements.3) Connectivity/data integrityconsiderations: Modularity in the battery-

Figure 3: The LTC6804 MulticellBattery Monitor IC providesaccurate, precise measurements onstacked battery cells, which are thestarting point for a successful BMSimplementation

Figure 4: The LTC6804 supports an isolated SPIinterface which can be “daisy-chained” forlarger arrays, which results in a robust, EMI-resistant interconnect which also minimizescabling requirements and the number ofisolators


28 BATTERY MANAGEMENT www.linear.com, www.nuvation.com


pack design adds to scalability,serviceability, and form-factor flexibility.However, this modularity requires that thedata bus between packs has galvanicisolation (no ohmic path), so failures inany one pack do not affect the rest of thesystem or put high voltages on the bus.Further, the wiring between packs musttolerate high levels of EMI.A two-wire isolated data bus is a viable

solution to achieve these goals in acompact and cost-effective way. Therefore,the LTC6804 offers an isolated SPIinterconnect called isoSPI, which encodesthe signals for clock, data in, data out, andchip select into differential pulses, whichare then coupled through a transformer arugged, reliable, and long-establishedisolation component (Figure 4).Devices on the bus can be connected in

a “daisy chain” configuration, whichreduces harness size and enables modulardesigns for large, high-voltage batterypacks, while maintaining high data ratesand low EMI susceptibility (Figure 5).To demonstrate the noise immunity,

Linear Technology performed BCI testingon the LTC6804. This involved coupling100 mA of RF energy into the battery-wiring harness, with the RF carrier sweptfrom 1 MHz to 400 MHz and with 1 kHzAM modulation on the carrier. TheLTC6804 digital filter was programmed fora 1.7 kHz cutoff frequency, and an externalRC filter and ferrite choke were added aswell. The result: the error in voltage readingwas below 2 mV over the entire RF sweeprange.An array of self-assessment and self-test

features adds to the suitability of the

LTC6804 for BMS applications. Thesechecks include open-wire detection; asecond internal reference for ADC clock;multiplexer self-test, and evenmeasurement of its internal power-supplyvoltages. The device is engineered forsystems that are intended to be compliantwith ISO 26262 and IEC 61508 standards.

ConclusionThere’s a lot of “glamour” associated withbackup and carry-through supplies for grid-level systems. It seems so straightforward:just keep an array of batteries charged(whether from the grid-AC line, or solar,wind, or other renewable sources), thenuse the batteries with a DC/AC inverterwhen you need to provide line-equivalentAC power. The reality is that batteries arenot “simple” in any of their behavior orperformance characteristics, and they needcarefully controlled charging, monitoring oftheir voltage, current, and temperature,and discharging. As power levels increase,a practical, efficient, and safe system is nota trivial design, and so a grid-connectedmulticell BMS is a complex system. Manyunique problems need to be understoodand addressed, with safety a majorconcern as well. A successful and viablesystem design needs a modular,structured, top-down architecture that issupported from bottom up by optimizedcomponents such as the LTC6804. Whencombined with sophisticated, secure data-acquisition and control software, the resultis a high-performance, reliable BMS thatrequires minimal operator involvement,and will function autonomously for yearsof reliable service.

Linear Technology announced end of 2015 the LTC6811high voltage (75 V) battery stack monitor, a drop-inreplacement for the former introduced LTC6804 withhigher performance and 25 % lower price. The LTC6811 isa complete battery measuring IC for hybrid/electricvehicles that incorporates a deep buried Zener voltagereference, high voltage multiplexers, 16-bit delta-sigmaADCs and a 1 Mbps isolated serial interface. An LTC6811can measure up to 12 series-connected battery cellvoltages with better than 0.04 % accuracy. With 8programmable 3rd order low pass filter settings, theLTC6811 provides outstanding noise reduction. In thefastest ADC mode, all cells can be measured within 290 µs.

For large battery packs, multiple LTC6811s can beinterconnected and operated simultaneously, using aproprietary 2-wire isoSPI™ interface. This built-in interfaceprovides electrically isolated, high RF noise immunecommunication for data rates up to 1 Mbps. Usingtwisted pair, many LTC6811s can be connected in a daisychain to one host processor, enabling the measurement ofhundreds of cells in high voltage battery stacks. The

LTC6811 is specified for operation from �40°C to 125°C.It has been engineered for ISO 26262 (ASIL) compliantsystems with extensive fault coverage via its redundantvoltage reference, logic test circuitry, cross-channel testing,open wire detection capability, a watchdog timer andpacket error checking on the serial interface.

For existing designs using LTC6804 battery stackmonitor, the LTC6811 is a drop-in replacement withadditional filter cutoff frequencies, added passive andactive balancing control features, new ADC commandsand enhanced fault coverage for functional safety. TheLTC6811 is supported by Linear’s Linduino™ technology,an Arduino-based microcontroller board and softwarelibrary. The microcontroller board includes an electricallyisolated USB port and directly connects to the LTC6811demonstration board, providing a simple platform forevaluating and developing the application. The LTC6811 isoffered in a 8 mm x 12 mm surface mount SSOP package.Priced at $8.19 each in 1,000-piece quantities, samplesand demonstration boards are available atwww.linear.com/product/LTC6811.

Improved Battery Stack Monitor

Figure 5: Test results on the LTC6804 and isoSPI interface showed no data errors despite 200 mA ofinjected RF with the isoSPI operating at 20 mA signal strength


www.tmi.yokogawa.com/ea/ POWER ELECTRONICS MEASUREMENT 29


Testing Power ElectronicSystems EfficientlyWith today’s increased incorporation of power electronics and switching devices in overall system design,there is a growing need for accurate measurement of both the power behavior of the applied powerelectronics and other inter-related electrical and physical parameters. Clive Davis, Marketing Manager,Test and Measurement, Yokogawa Europe & Africa

It may be surprising to learn that thereis no accredited traceability for powermeasurement calibration anywhere in theworld above 200 kHz. Indeed there areonly five calibration laboratories which canperform ISO 17025 accredited powercalibrations at 100 kHz. This naturallyaffects the validity of powermeasurements, particularly in switchingapplications where higher frequencies arepresent. There are a variety of productsavailable to measure power, the selectionof which will depend on a number offactors, including the stage of thedevelopment of the power electronicsproduct and the desired accuracy of themeasurement.

Architecture and designAt the architecture and design stage, weare considering the development ofindividual parts, and measurements

include characteristics such as fast inverterswitching, high-frequency dynamicbehavior, overshoot on pulses, and theneed to trigger on individual waveforms. Amixed-signal oscilloscope with up to eightinput channels to view input and outputsignals in three-phase systems can beused to make these measurements(Figure 1). With a waveform-displayingproduct, such as an oscilloscope, it canseem easier to understand powermeasurement as even standardmeasuring features can be used to derivethe value of active power. However,consideration must be given to both theaccuracy and the stability of themeasurement. Accuracy specifications ofoscilloscopes do not include those forpower measurement and generally do noteven include any for AC voltagemeasurements.

So, although IGBT and SiC MOSFET

switching losses, for example, can bemeasured using dedicated oscilloscopefeatures, the absolute accuracy is notspecified, and it is difficult to estimate theerrors. Possible sources of error include theinaccuracy of the scope, the inaccuraciesof the probes and the phase differencesbetween them. In power measurement,phase differences can be a major sourceof error. The error from phase differencescan be reduced, however, by using theautomatic probe anti-skew feature ifavailable. Thus, by paying attention to themeasurement and perhaps using areference circuit, an oscilloscope canindeed be used to judge if a circuitmodification has increased or reduced thelosses.

Verification and prototypingThe next stage is verification andprototyping, at which the individual parts

Figure 1: TheDLM4000 mixed-signal oscilloscopeoffers up to eightinput channels toview input andoutput signals inthree-phase systems

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30 POWER ELECTRONICS MEASUREMENT www.tmi.yokogawa.com/ea/


are combined and form the system undertest. To understand the dynamics of theapplication requires the measurement andanalysis of a combination of electrical,mechanical and physical signals and, inautomotive applications, signals frombuses such as CAN and LIN (Figure 2).For this type of measurement,ScopeCorders are used. As a portable dataacquisition recorder, a ScopeCorder cancapture and analyze both transient eventsand trends for long periods. Using flexiblemodular inputs, it can combinemeasurements of electrical signals,physical parameters from sensors andCAN and LIN serial buses, and can triggeron electrical power related and othercalculations in real time.

Efficiency validationIn the efficiency validation stage, the keyfactors that need to be tested are poweranalysis, conversion efficiency, harmonicsand, for instance, the battery charge anddischarge process. For tests of this type,

the instrument of choice is the poweranalyzer, offering high precision, highaccuracy, high stability, and the ability tocarry out calibrated measurements. A keydifference therefore between anoscilloscope type product and a poweranalyzer is that a power analyzer is fullyspecified for power measurement andvoltages and currents are connecteddirectly.

At this point, in order to select anappropriate instrument, the user alsoneeds to consider what absolute accuracyis required for the power measurements,the frequencies in the signal and how this accuracy is proven. Where smallimprovements in input/output efficiencyare being sought, for example for PVinverters, where efficiencies are typically95 to 98 %, small improvements can onlybe recognized if the accuracy of themeasuring instrument is at the highestlevel. With an ISO 17025 accreditedcalibration at frequencies up to 100 kHz, itis possible to not only prove the specified

accuracy but also achieve much betterperformance than the specification (Figure 3).

Hybrid instrumentsIn addition to the dedicated instrumentsdescribed above, engineers and R&Dprofessionals are also looking for hybridinstruments that can be used at all stagesof the development cycle. When thepower consumed by the load varies – forexample during the start-up of a motor – itmay be necessary to measure power atmuch shorter intervals. A specificrequirement is to provide the time-basedmeasurement functionality of anoscilloscope combined with the accuracyof a power analyzer (Figure 4).Instruments such as precision powerscopes provide users with flexibility,accuracy and wide bandwidth, allowingthem to draw together the range of powerreadings needed to optimize the efficiencyof boost circuits and inverters – two keyelements in overall electric vehicle

Figure 2: Schematic of an electric car drive train, illustrating the various signals that need to be measured at the verification and prototyping stage

Figure 3: The WT3000 precision power analyzer


www.tmi.yokogawa.com/ea/ POWER ELECTRONICS MEASUREMENT 31


performance.Like a power analyzer, a precision power

scope is capable of accurately measuringsteady-state power and related variables,since they share the same inputtechniques and measurement principles.However, as it also shares characteristics ofoscilloscopes and ScopeCorders, it iscapable of capturing and measuring thepower arbitrarily over any part of the powerwaveform using start and stop cursors. Thisis particularly useful for examining transientphenomena and in the design ofperiodically controlled equipment. Thetrigger functionality helps to set varioustrigger conditions based on the analysis ofthe transient phenomena to understandthe behavior of the system under test.During the start-up phase of an inverterand motor in an electric or hybrid car, forexample, current increases can beanalyzed in each cycle (Figure 5). And,when the load changes rapidly, theengineers can gain insights that will enable

them to improve the control of theinverter.

The need for calibrationAs more and more innovation focuses onenergy efficiency and the use of renewableenergy resources, engineers are increasinglydemanding accuracy and precision fromtheir power measurements. At the sametime, new standards such as IEC62301Ed2.0 and EN50564:2011, coveringstandby power consumption, and the SPECguidelines, covering power consumption indata centers, demand more precise andaccurate testing to ensure compliance.

To meet these challenges, R&D teamsare coming to terms with the need for newlevels of precision in power measurement,but these levels of precision can only beachieved if the measuring instruments areproperly calibrated with reference tonational and international standards.

Regular calibration by a laboratory, whichcan provide very low measurement

uncertainties at the specific measurementpoints applicable to individual users,should enable instrument makers and theircustomers to have confidence in their testresults.

Laboratories that are accredited to ISO17025 (General requirements for thecompetence of testing and calibrationlaboratories), however, have demonstratedthat they are technically competent andable to produce precise and accuratecalibration measurements. Yokogawa’sEuropean Calibration Laboratory is the onlyindustrial (i.e. non-government or national)organization to offer traceability up to 100kHz, and makes it the only power metermanufacturer which can directly prove theperformance of its own instruments.

LiteratureClive Davis, Erik Kroon, “The Need for

High-Frequency High-Accuracy PowerMeasurement”, Power ElectronicsEurope 6/2015, pages 29 - 31

Figure 4: The PX8000Precision PowerScope

Figure 5: During thestart-up phase of aninverter and motor inan electric or hybridcar, for example, thePrecision PowerScope allows currentincreases to beanalysed in eachcycle


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Thyristors

Smartpower Devices

Voltage References

Power ICs

Power Amplifiers

Switches & Relays

Switched Mode PowerSupplies

Switched Mode PowerSupplies

Thermal Management &Heatsinks

Thermal Management &Heatsinks




www.neutronltd.co.ukNeutron LtdTel: +44 (0)1460 242200

www.rubadue.comRubadue Wire Co., Inc.Tel. 001 970-351-6100








www.fujielectric-europe.comFuji Electric Europe GmbHTel: +49 (0)69-66902920




www.ar-europe.ieAR EuropeTel: 353-61-504300



www.universal-science.comUniversal Science LtdTel: +44 (0)1908 222211

www.power.ti.comTexas InstrummentsTel: +44 (0)1604 663399


www.dau-at.comDau GmbH & Co KGTel: +43 3143 23510

www.power.ti.comTexas InstrummentsTel: +44 (0)1604 663399


www.isabellenhuette.deIsabellenhütte Heusler GmbH KGTel: +49/(27 71) 9 34 2 82

ADVERTISERS INDEX

Mosfets

Magnetic Materials/Products

Line Simulation

Optoelectronic Devices

Packaging & Packaging Materials


www.biaspower.comBias Power, LLCTel: 001 847 215 2427www.digikey.com/europe

Digi-Key Tel: +31 (0)53 484 9584


www.digikey.com/europeDigi-Key Tel: +31 (0)53 484 9584




www.abl-heatsinks.co.ukABL Components LtdTel: +44 (0) 121 789 8686

www.hero-power.com Rohrer GmbH Tel.: +49 (0)89 8970120

www.rohrer-muenchen.deRohrer GmbHTel.: +49 (0)89 8970120


APEC .............................................................................................................................................................4

DFA Media ...................................................................................................................................20 & 24

Drives & Controls 2016 ......................................................................................................................32

Fuji Electric ..............................................................................................................................................IFC

Graftech ....................................................................................................................................................21

HKR.............................................................................................................................................................27

LEM ...............................................................................................................................................................7

PCIM ........................................................................................................................................................IBC

Proton-Electrotex....................................................................................................................................17

Semikron...............................................................................................................................................OBC

Toshiba ......................................................................................................................................................12

V.M.I. ...........................................................................................................................................................19




Website Locator.qxp_p41-42 Website Locator 04/02/2016 11:44 Page 34

Connecting Global Power

International Exhibition and Conferencefor Power Electronics, Intelligent Motion,Renewable Energy and Energy ManagementNuremberg, 10 – 12 May 2016

More information at +49 711 [email protected] or pcim-europe.com

PCIM_EU_2016_ANZ_E_210x297.indd 1 05.10.15 11:0535_pee_0116.indd 1 04/02/2016 10:12

125kW up to 250kW

Available in 1200V/1700V from 300A to 600A

Standard Industry Package, optional with integrated shunt resistors

Integrated bundle saves R&D time, material and production cost

Plug-and-Play driver with isolated current/voltage/temperature signal

Pre-applied Phase Change Material with optimized thermal performance

Motor Wind Solar Power Power Urban TransportDrives Energy Energy Quality Supplies Equipment

Integrated Shunts

Phase Change Material

Driver Bundle

SEMiX ®3 Press-Fit

It’s Your Choice!

210 x 297

Standard Industry Package

www.semikron.com shop.semikron.com

36_pee_0116.indd 1 04/02/2016 10:10

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