* Ph.D.Eng.WojciechMysiński,Ph.D.Eng.WiesławJakubas,InstituteofElectrotechnicsandComputerScience,FacultyofElectricalandComputerEngineering,CracowUniversityofTechnology.

WOJCIECHMYSIŃSKI,WIESŁAWJAKUBAS*

GATEDRIVERFORSiCMOSFETTRANSISTORS

STEROWNIKBRAMKITRANZYSTORÓWMOSFETSiC

A b s t r a c t

Asnewpowertransistors,suchasSiCMosfets,arebeingincreasinglyusedinpowerelectro-nicssystems,ithasbecomenecessarytousespecialdrivers.Thisarticlecomparestheparame-tersofSiCMosfet,SiMosfet,andIGBTgatecircuits.Differencesarediscussedwithreferencetothewaysinwhichthesetransistorsarecontrolled.GatecircuitparametersofSiCtransistorsdifferslightlyfromthoseofcommonMosfetorIGBTtransistors,andinordertobeabletofullyutilisethecapabilitiesofthesenewdevices,itisnecessarytoemployappropriatedrivers.ThisarticlediscussesonesuchdriverforSiCtransistors.

Keywords: SiC Mosfet, gate driver

S t r e s z c z e n i e

ZewzględunacorazczęstszestosowanienowychtranzystorówmocytypuMosfetSiCwukła-dachenergoelektronicznychistniejepotrzebazastosowaniaspecjalnychukładówsterownikówbramek.ParametryobwodubramkitranzystorówzbudowanychnawęglikukrzemusątrochęinneniżtypowychtranzystorówMosfetlubIGBTiżebywpełniwykorzystaćwłaściwościtychnowychelementów,należyzastosowaćodpowiedniesterowniki.Wartykuleprzedstawionoje-denzprzykładówsterowników(tzw.gate driver)dlatranzystorówtypuMosfetSiC.

Słowa kluczowe: tranzystor Mosfet SiC, sterownik bramki

TECHNICAL TRANSACTIONSELECTRICAL ENGINEERING

1-E/2016

CZASOPISMO TECHNICZNEELEKTROTECHNIKA

DOI: 10.4467/2353737XCT.16.033.5295

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1. Primary differences between Si and SiC MOSFETs

Silicon carbide-based power transistors have been around for several years and havebeen discussed in numerous scientific publications [4–6, 9, 11]. SiC diode and transistormanufacturerscontinuetoaddnewversionsofsuchtransistorstotheiroffering.

MainadvantagesofSiCMOSFETs,ascomparedwithSiandIGBTMOSFETs,include:• highswitchingspeed,shorterturn-onandturn-offtimes,• lowerswitchinglosses,• lowerconductionlosses,alowerVDSdropforhighvoltagedevices.

Disadvantages:• highergatevoltageVGSisrecommendedinordertoachievelowVDSdrop,e.g.20V,• costsofSiCdevices,• differencesbetweentheperformancecharacteristicsofgatecircuitsindevicesmadeby

differentmanufacturers.Inshort,itmaybesaidthatconvertersbasedonSiCdevicesexhibithigherefficiency,

and their higher switching frequency enables designers to use smaller inductive devices.Unfortunately,highcurrentandvoltagerisevaluescancauseelectromagneticinterferenceproblems;therefore,theelectro-mechanicaldesignofconvertersneedstobepreparedverycarefully.Table1showsacomparisonofthekeyparametersofgatecircuitsinSiCMosfet,SiMosfetandIGBTtransistorsfora25°CoperatingtemperatureandsimilarIDandVDS values.

OneofthemajordifferencesbetweenSiCtransistors,MOSFETsandIGBTsistheirinputandoutputcharacteristics.Figures1and2showtheoutputcharacteristicsofthetransistors,draincurrent IDSversusdrain-sourcevoltageVDS forvariousVGSorVGEvalues inan IGBT.Ascanbeseen,inaSiCMosfettransistor,theVGSvoltagehasasignificanteffectonthedraincurrentandvoltagedropVDSacrossthetransistor.

T a b l e 1

Basic differences between the gate circuits of selected transistors

Transistor type

Manufa- cturer

Nominalparameters

VDS/ID[V]/[A]

Maxgatevoltagerange

VGS[V]

Recommendedgatevoltage

rangeVGS[V]

Recommen- dedgate

resistanceRG [Ω]

Drain–source

voltageVDS at25°CandID =40A,

[V]

C2M0040120–SiC Cree 1200/40 –10/+25 –5/+20 2.5 1.8

SCH2080KE–SiC Rohm 1200/40 –6/+22 0/+18 0 3.8

SCT30N120–SiC ST 1200/45 –10/+25 –2/+20 6.9 3.5

STE40NC60–Mosfet ST 600/40 –30/+30 0/+10 4.7 4

STGFW40V60DF–IGBT ST 600/40 –20/+20 VGE =0/+15 10 1.8

RGT80TS65D–IGBT Rohm 650/40 –30/+30 VGE =0/15 10 1.65

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MaximumdraincurrentIDcanassumesignificantlydifferentvalueswithintheVGS range10–20V.ThesmallestvoltagedropVDS(drain-source)acrossthetransistorandconsequently,thelowesttransistorconductionloss,isachievedforVGS =20V(Fig.1).

Output characteristics of theSiCMOSFET andSiMOSFET and IGBT are different.ForSiMOSFETandIGBTtransistors,themaximumdraincurrentIDcanbeachievedataslowVGSvoltageas10–15V,andifthevoltagecontinuestobeincreasedfurther,thiswillnotproduceasignificantdifferenceinthevalueofvoltagedropsacrossthetransistor(Fig.2).Thisimpliesthat,withrespecttoSiCtransistors,itisadvisabletoapplythemaximumgatevoltage,asrecommendedbythemanufacturer,sothatconductionlossesshouldbeasminimalaspossible.Dependingonthemanufacturer,therecommendedvoltagemayvaryoverarangeofca.+18Vto+22V.Itshouldbeemphasisedthatthemaximumallowablegatevoltageshouldnotbeexceeded,asthiswillleadtothedevicebeingdamaged.Insuchtransistors,themaximumpositiveallowablegatevoltagevariesoverarangeof+22Vto+25V,dependingon themanufacturer (Table1).Fora transistor tobe turnedoffquickly, thedrivershouldsupplyanegativevoltagetothegate.InrespectofSiCtransistors,manufacturersrecommendthat a negative voltage in the range of ca. –5V to 0V should be applied.However, themaximumnegative allowable gate voltageVGS varies over a range of ca. –10V to –6V,dependingonthemanufacturer.Ontheotherhand,themaximumallowablegatevoltageVGE orVGSforIGBTsandMosfetsvariesovertherangeca.–20Vto+20V.

Fig.1.OutputcharacteristicsofaSiCC2M004120DtransistorfromCree(a),andofaRohmSiCSCH2080KEtransistor(b)andmeasurementcircuit(c)

a)b)

c)

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Fig.2.OutputcharacteristicsofanIGBTSTGFW40V60DFtransistorfromST(a)andofaMosfetSTE40NC60transistor,alsoproducedbyST(b)

T a b l e 2

Gate circuit parameters – recommended VGS and RG values for a SCT2160KE transistor, from Rohm

Parameter Symbol ConditionsValues

UnitMin. Typ. Max.

Transconductance gfs VDS=10V,ID=7A – 2.4 – SInputcapacitance ciss VGS=0V – 1200 –

pFOutputcapacitance goss VDS=800V – 45 –Reversetransfercapacitance grss f=1MHz – 7 –

Effectiveoutputcapacitance,energy

relatedc0(er)

VGS=0V VDS=0Vto500V

– 71 – pF

Tum–ondalaytime td(on) VDD=400V,ID=7A – 23 –

nsRisetime tr VGS=18V/0V – 25 –

Tum–offdelaytime td(off) RL=57Ω – 67 –Falltime tf VG=0Ω – 27 –

Tum–onswitchingloss Eon

VDD=600V,ID=7AVGS=18V/0V

RG=0Ω,L=500μHEon included

diodereverserecovery

– 126 –

μJTum–offswitching

loss Eoff – 55 –

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Ontheirdatasheets,transistormanufacturersprovideinformationontherecommendedgatevoltagerangesaswellasgateresistance,sothatoptimalswitchingparameterscouldbeachieved(Table2).Theproperselectionofaseriesresistorforthegatecircuithasasignificanteffectontheswitchingtimeparametersofthetransistor.

Onecoulduseeitherasingleresistancevalueortwodifferentvalues;thelatteroptionwillhaveagreatereffectontransistorturn-onandturn-offdelaytimes.This,inturn,willhaveaneffectontherateofcurrentandvoltagerisesinthepowercircuitaswellasswitchinglosses(Fig.3).Ontheonehand,increasingthevalueofaresistorwillslowdowntheswitchingofthetransistorandwillleadtohigherswitchinglosses;ontheotherhand,ithelpstoavoidoscillationsinthegatecircuitandthepowercircuit,which,inturn,reducesEMCinterferencegeneratedbythetransistor.

Fig.3.EffectofthegateresistorRGonswitchinglosses(a)andswitchingtimes(b),foraSiCC2M0040120DtransistorfromCree

a)

b)

2. Gate drivers for SiC transistors

At present,manufacturers offermany ready-made integrated circuits that are used asdriversforunipolartransistorsandcouldalsobeusedtodriveSiCtransistors;however,careneedstobetakentoensurethatthedeviceusedcansupplyanoutputvoltagewithintherangeca.+20Vto+22V.Notallintegratedcircuitsonthemarketmeetthisrequirement.Itisalsopossibletobuildadriverusingdiscretedevices,suchasthoseshowninFigures4and5.

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Fig.4.Sampledrivercircuitbasedondiscretedevices[10]

Fig.5.AnotherdriverproducedbyRohm[11]

Bysimplyusingadiodeinthegatecircuit(Fig.4),thevalueofseriesresistanceinthegatecanbechanged;seriesresistancecantakeondifferentvaluesuponthetransistorbeingturnedonand turnedoff.That isaverycommonsolutionemployed indrivercircuits fortransistors,bothSiCandMosfetsaswellasIGBTs.

3. Designing, building and testing a driver

Inorder tobuildadriverforaSiCtransistor, theauthorsusedproductdocumentationdevelopedbytheCreecompany,whichkindlymadeavailablearticlesonanisolateddriver[3,8].Usingthematerialsprovided,aftermakingcertainmodifications,theauthorsdesignedandbuiltadriver forwhichaschematic isshowninFigure6.AnIXDN609SI integratedcircuit,intendedforusewithIGBTs,MOSFETsandSiCs,isemployedasakeydeviceinthedriver(U1).

KeyparametersofanIXDN609integratedcircuitfromIXYS:• maximumpeakoutputcurrent(sourceandsink)IOUT =±9A,• widesupplyvoltagerangeVcc =4.5Vto35V,• operatingtemperaturerangeof–40°Cto+125°C,

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• inputvoltagerangeVIN:–5VtoVcc+0.3V,• risetimetf =22ns,falltimetf =15ns,on-timedelayton =40ns,off-timedelaytoff =42ns

forVcc =18VandCobc =10nF,• quiescentsupplycurrent10μA,• lowoutputimpedanceROH =0.6Ω,ROL =0.4Ω.

Inordertoprovidegalvanicisolationfortheentiredriver,isolatedDC/DCconvertershavebeenusedandtheso-calleddigitalisolator–anADUM1100isolatorfromAnalogDevicesfortransmittingasignaldrivingthetransistor.ThankstothecurrentefficiencyofcircuitU1,thedrivercanbeusedtodrivebothindividualtransistorsandhighpowertransistormodulesincorporatingseveraltransistorsconnectedinparallel.

Thecircuitthattheauthorsdesignedandbuilthasthefollowingfeaturesandcharacteristics:• fullgalvanicisolationinrespectofpowersupplyandcontrol,• driverpowersupplyvoltage+5V,• aTTLinputsignal(+5V),alogic‘1’,activestate,• voltageacrossthetransistorgate,on-state–5V,off-state+20V,• switchingtimesarethesameasU1(IXDN609),andtheyareadditionallydeterminedby

theresultantgateresistancevalueupontransistorturn-on,andaseparateresistancevalueupontransistorturn-off.

Fig.6.SchematicofthedriverforaSiCMosfettransistor

Comparedwiththeoriginalcircuitincorporatingthematerials[3],theactualcircuitbuiltwasmodifiedbyreplacingtheACPL-4800-300EopticalcouplerwiththeADUM1100digitalisolatorandaddinganextravoltagelinearstabiliser,sothatgatevoltageof+20Vcouldbeachieved.Thedriveroutputvoltagevalues(–5V,+20V)wereadapted toaSCT2160KEtransistor,madebyRohm.

Fortheentirecircuittooperate,itisnecessarytoprovideanumberofsupplyvoltages.Voltageof–5VforturningoffthetransistorissuppliedbytheisolatedDC/DCconverter(+5

120

Vinto+5V)(PS1).Voltageof+20VforturningonthetransistorissuppliedbytheisolatedDC/DCconverter(+5Vinto±12V)(PS2).TheoutputofconverterPS2provides+24V(ifloadconnectedtotheconverterissmall,outputvoltagecanbeashighas+26V),soinordertoachieve+20V,alinearstabilisercircuitwasaddedacrosstransistorQ2.ToenabledigitalisolatorISO1tooperate,theauthorsuseda+5VlinearstabiliseracrossZenerdiodeD1andtransistorQ1.Thedrivermodule is installedona50×40mmdouble-sidedprintedcircuitboard,withthedevicesmountedonbothsidesofthePCB(Fig.7).

TheoutputofU1comprisesparallelresistorsanddiodeD1;thesedevicesallowtheusertosettheresistancelevelrequiredtoturnonandturnoffthetransistor.Peakgatecurrentvaluescanreachseveralamperesandthatiswhythegateresistorneedstohaveasufficientpowerratingtoallowfordissipationofpowerasheat thatwillbeemitted,particularlyathigh switching frequencies. It is imperative that the so-called coupling capacitors shouldblock+20Vand–5VsupplyvoltagesincloseproximitytoU1andtheSiCtransistor.Thesecapacitorsshouldhavelowinternalresistance.Theconnectionbetweenthedriverandthetransistorshouldbekeptasshortaspossibleinordertominimiseconnectioninductancesandthustominimiseoscillationsinthegatecircuit[3–5].

Fig.7.PCBusedtobuildthedriver

The2WDC/DCconvertersandthedigitalisolatorprovidegalvanicisolationofupto1.5kV,sothedrivercanbeusedforcircuitssuppliedwithvoltagesupto600V.Iftheinverteristooperateathighervoltages,itisnecessarytouseconvertersdesignedforisolationvoltageof3kV.

Figure9 shows the resultsof laboratory testson thedriver.Thewaveforms representcontrol voltage VS (Ch1), gate-source voltage VGS (Ch2) and gate current IG (Ch4).AnSCT2160KE transistorwasconnectedwithout the load;draincurrent ID =0Aanddrain-sourcevoltageVDS =0V.

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Fig.8.ControlvoltageVS (Ch1–2V/div),gatevoltageVGS (Ch2–10V/div),gatecurrentIG (Ch4–1A/div).GatevoltageVGS –5V,+20V,RG =3.3Ω

As canbe seen, the turn-ondelay time is 40ns, and the turn-off delay time–43ns.Thesevaluesweremeasuredwithoutanyloadconnectedtothepowercircuitofthetransistor.Figure9shows6driversincorporatedinatestmodelthree-phaseinverter.

Fig.9.Inverterincorporatingtransistordrivers

4. Conclusions

Thedriverdesignedbytheauthorsdeliverstherequiredperformanceandhasbeenusedintestsofathree-phaseinverter.TheuseofSiCtransistorsrequiresspeciallydesigneddrivers.ThatiswhystandarddriversusedtodriveMOSFETsandIGBTsarenotalwayssuitableforusewithSiCdevices.

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The driver built by the authors is designed only to turn on and turn off transistors;acompletedrivershouldalsoprovideovercurrentprotection.TheoutputcircuitofthedriverexhibitssufficientcurrentefficiencytocontrolaSiCtransistormodulethat,forexamples,hasamaximumdraincurrentID=100A.Wheredeviceshavelowerpowerratings,integratedcircuitshavingloweroutputcurrentcanbeused.AcomparisonofthecharacteristicsofthegatecircuitsofSiCMOSFETtransistorsfromanumberofmanufacturersshowsthattherearedifferencesbetweenthesedevicesinrespectoftherecommendedcontrolvoltage.

Inorder to fullyutilise thecapabilitiesofSiC transistors, themaximumgatevoltagesrecommendedbytransistormanufacturersshouldbeused.

R e f e r e n c e s

[1] AbuishmaisI.,BasuS.,UndelandT.,On Driving SiC Power JFETs,14thInternationalPowerElectronicsandMotionControlConference,EPE-PEMC2010.

[2] CallananB.,Application Considerations for Silicon Carbide MOSFETs,Creeproductliterature,http://www.cree.com[online:2.06.2016].

[3] CallananB.,SiC MOSFET Isolated Gate Driver,Creeproductliterature,http://www.cree.com [online:2.06.2016].

[4] GóreckiK.,ZarębskiJ.,Charakterystyki statyczne i parametry tranzystorów MOSFET mocy z krzemu i z węglika krzemu,„Elektronika:konstrukcje,technologie,zastosowa-nia”,Sigma-NOT,9/2012,pp.94–97.

[5] Handbook of Power devices,Rohmproductliterature,http://www.rohm.com [online:2.06.2016].

[6] HapkaA., JankeW., Kraśniewski J., OleksyM.,Charakterystyki DC tranzystorów MOSFET SiC oraz Si pracujących w obszarze silnego przewodzenia, w szerokim za-kresie temperatur,„Elektronika:konstrukcje,technologie,zastosowania”,Sigma-NOT,9/2012,pp.98–101.

[7] PeftitsisD.,On Gate Drivers and Applications of Normally-ON SiC JFETs,DoctoralThesis,KTHElectricalEnergyConversionSchoolofElectricalEngineeringSE-10044Stockholm,Sweden2013.

[8] Richmond J.,Hard-Switched Silicon IGBTs? Cut Switching Losses in Half with Sili-con Carbide Schottky Diodes, Cree product literature, http://www.cree.com [online:2.06.2016].

[9] RoundS.,HeldweinM.,KolarJ.,HofsajerI.,FriedrichsP.,A SiC JFET Driver for a 5 kW, 150 kHz Three-Phase Sinusoidal-Input, Sinusoidal-Output PWM Converter,https://www.pes.ee.ethz.ch/uploads/tx_ethpublications/round_IAS05.pdf [online:2.06.2016].

[10] RubinoB.,CatalisanoG.,AbbatelliL.,BuonomoS.,Comparative analysis of driving approach and performance of 1.2 kV SiC MOSFETs, Si IGBTs, and normally-off SiC JFETs,STproductliterature,http://www.st.com[online:2.06.2016].

[11] SiC Power Devices and Modules. Application Note,Rohmproductliterature,IssueofAugust2014,http://www.rohm.com[online:2.06.2016].