Application Notes 2006 2nd Edition

8/12/2019 Application Notes 2006 2nd Edition

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DC-DC Converter ApplicationsDC-DC Converter ApplicationsTerminologyThe data sheet specification for DC-DC con-verters contains a large quantity of infor-mation. This terminology is aimed at ensu-ring that the user can interpret the data pro-vided correctly and obtain the necessaryinformation for their circuit application.

Input RangeThe range of input voltage that the devicecan tolerate and maintain functional perfor-mance over the Operating TemperatureRange at full load.

Load RegulationThe change in output voltage over the spe-cified change in output load. Usually speci-fied as a percentage of the nominal outputvoltage, for example, if a 1V change in out-put voltage is measured on a 12V outputdevice, load voltage regulation is 8.3%. Forunregulated devices the load voltage regula-tion is specified over the load range from10% to 100% of full load.

Line Voltage RegulationThe change in output voltage for a givenchange in input voltage, expressed as per-centages. For example, assume a 12V in-put, 5V output device exhibited a 0.5V

change at the output for a 1.2V change atthe input, line regulation would be 1 %/1%.

Output Voltage AccuracyThe proximity of the output voltage to thespecified nominal value. This is given as atolerance envelope for unregulated deviceswith the nominal input voltage applied. Forexample, a 5V specified output device at100% load may exhibit a measured outputvoltage of 4.75V, i.e. a voltage accuracy of5%).

Input and Output Ripple and Noise

The amount of voltage drop at the input, oroutput between switching cycles. The valueof voltage ripple is a measure of the storageability of the filter capacitors. The valuesgiven in the datasheets include the higherfrequency Noise interference superimposedon the ripple due to switching spikes.Themeasurement is limited to 20MHzBandwidth.

Input to Output IsolationThe dielectric breakdown strength test be-tween input and output circuits. This is the

isolation voltage the device is capable ofwithstanding for a specified time, usually 1 se-cond (for more details see chapter IsolationVoltage vs. Rated Working Voltage).

Insulation ResistanceThe resistance between input and output cir-cuits. This is usually measured at 500V DCisolation voltage.

Efficiency at FulI LoadThe ratio of power delivered from the deviceto power supplied to the device when thepart is operating under 100% load condi-tions at 25C.

Temperature DriftThe change in voltage, expressed as a per-centage of the nominal, per degree change inambient temperature. This parameter is rela-ted to several other temperature dependentparameters, mainly internal component drift.

Switching FrequencyThe nominal frequency of operation of theswitching circuit inside the DC-DC conver-ter. The ripple observed on the input andoutput pins is usually twice the switchingfrequency, due to full wave rectification andthe push-pull configuration of the driver circuit.

No Load Power ConsumptionThis is a measure of the switching circuitspower cunsumption; it is determined withzero output load and is a limiting factor forthe total efficiency of the device.

Isolation Capacitance

The input to output coupling capacitance.This is not actually a capacitor, but the para-sitic capacitive coupling between the trans-former primary and secondary windings.Isolation capacitance is typically measuredat 1 MHz to reduce the possibility of the on-board filter capacitors affecting the results.

Mean Time Between Failure (MTBF)RECOM uses MIL-HDBK-217F standard forcalculation of MTBF values for +25C aswell as for max. operating temperature and100% load. When comparing MTBF values

with other vendor's products, please takeinto account the different conditions andstandards i.e. MIL-HDBK-217E is not as severeand therefore values shown will be higher thanthose shown by RECOM. (1000 x 10 hours=1000000 hours = 114 years!)These figures are calculated expected devi-ce lifetime figures using the hybrid circuitmodel of MIL-HDBK-217F. POWERLINE con-verters also can use BELLCORE TR-NWT-000332 for calculation of MTBF. The hybridmodel has various accelerating factors foroperating environment ( E ), maturity ( L ),screening ( Q ), hybrid function ( F ) and a

summation of each individual componentcharacteristic ( C ).

The equation for the hybrid model is thengiven by: = (NC C ) (1 + 0.2 E ) L F Q(failures in 106 hours)

The MTBF figure is the reciprocal of this value.In the data sheets, all figures for MTBF aregiven for the ground benign (GB) environ-ment ( E = 0.5); this is considered the mostappropriate for the majority of applicationsin which these devices are likely to be used.However, this is not the only operating envi-ronment possible, hence those users wis-hing to incorporate these devices into amore severe environment can calculate thepredicted MTBF from the following data.The MIL-HDBK-217F has military environ-ments specified, hence some interpretation

of these is required to apply them to stan-dard commercial environments. Table 1 givesapproximate cross references from MIL-HDBK-217F descriptions to close commer-cial equivalents. Please note that these arenot implied by MIL-HDBK-217F, but are ourinterpretation. Also we have reduced thenumber of environments from 14 to 6,which are most appropriate to commercialapplications. For a more detailed understan-ding of the environments quoted and thehybrid model, it is recommended that a full

copy of MIL-HDBK-217F is obtained.It is interesting to note that space flight andground benign have the same environmentfactors. It could be suggested that the act ofachieving space flight should be the determi-ning environmental factor (i.e. missile launch).

The hybrid model equation can therefore berewritten for any given hybrid, at a fixedtemperature, so that the environmental fac-tor is the only variable: = k (1 + 0.2 E )

The MTBF values for other environment fac-tors can therefore be calculated from theground benign figure quoted at each tempe-rature point in the data book. Hence predic-ted MTBF figures for other environmentscan be calculated very quickly. All the valueswill in general be lower and, since the majo-rity of the mobile environments have thesame factor, a quick divisor can be calcu-lated for each condition. Therefore the onlycalculation necessary is to devide the quo-ted MTBF fig. by the divisor given in table 2.

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DC-DC Converter ApplicationsDC-DC Converter Applications

Environment E E DivisorSymbol Value

Ground Benign GB 0.5 1.00

Ground Mobile GM 4.0 1.64

Naval Sheltered GNS 4.0 1.64

AircraftInhabited AIC 4.0 1.64Cargo

Space Flight SF 0.5 1.00

Missile Launch ML 12.0 3.09

Table 2: Environmental Factors

Environ- E MIL-HDBK-271F Commercial Interpretationment Symbol Description or ExamplesGround GB Non-mobile, temperature and Laboratory equipment, testBenign humidity controlled environments instruments, desktop PC's,

readily accessible to maintenance static telecommsGround GM Equipment installed in wheeled or In-vehicle instrumentation,Mobile tracked vehicles and equipment mobile radio and telecomms,

manually transported portable PC'sNaval NS Sheltered or below deck Navigation, radio equipmentSheltered equipment on surface ships or and instrumentation below

submarines deck Aircraft AIC Typical conditions in cargo Pressurised cabin compart-Inhabited compartments which can be ments and cock-pit, in flightCargo occupied by aircrew entertainment and non-safety

critical applicationsSpace SF Earth orbital. Vehicle in neither Orbital communications satel-Flight powered flight nor in atmospheric lite, equipment only operated

re-entry once in-situMissile ML Severe conditions relating Severe vibrational shock andLaunch to missile launch very high accelerating forces,

satellite launch conditions

Table 1: Interpretation of Environmental Factors

NoiseInput conducted noise is given in the lineconducted spectra for each DC-DC conver-

ter (see EMC issues for further details).Noise is affected significantly by PCB layout,measurement system configuration, termi-nating impedance etc., and is difficult toquote reliably and with any accuracy otherthan via a spectrum analysis type plot.There will be some switching noise presenton top of the ripple, however, most of this iseasily reduced by use of small capacitors orfilter inductors, as shown in the applicationnotes.

Operating temperature range:Operating temperature range of the conver-ter is limited due to specifications of thecomponents used for the internal circuit ofthe converter.

The diagram for temperature deratingshows the safe operating area (SOA) withinwhich the device is allowed to operate. Atvery low temperatures, the specifications

are only guaranteed for full load.Up to a certain temperature 100% powercan be drawn from the device, above thistemperature the output power has to beless to ensure function and guarantee spe-cifications over the whole lifetime of theconverter.

These temperature values are valid fornatural convection only. If the converter isused in a closed case or in a potted PCBboard, higher temperatures will be presentin the area around thermal converter becau-se the convection may be blocked.

If the same power is also needed at highertemperatures either the next higher wattageseries should be chosen or if the converterhas a metal case, a heatsink may be consi-dererd.

Calculation of heatsinks: All converters in metal-cases can have aheatsink mounted so the heat generatedby the converters internal power dissipati-on Pd can be removed. The general speci-

fication of the whole thermal system incl.heatsink is its thermal resistance

RTH case-ambient

Power dissipation Pd:

Figure 1: Standard Isolated Configurations

Figure 2: Alternative Supply Configurations

b) Non-lsolated Negative Rail

a) Non-lsolated Dual Rails

c) Dual Isolated Outputs (U/T)

c) Twin Isolated Outputs

b) Dual Output

a) Single Output

d PPP == in out PPout

outEfficiency

=R

THcase-ambient dP

Tcase Tambient

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IsolationOne of the main features of the majority ofRecom International Power GmbH DC-DCconverters is their high galvanic isolationcapability. This allows several variations oncircuit topography by using a single DC-DC

converter.The basic input to output isolation can beused to provide either a simple isolated out-put power source, or to generate differentvoltage rails, and/or dual polarity rails (seefigure 1).

These configurations are most often foundin instrumentation, data processing andother noise sensitive circuits, where it isnecessary to isolate the load and noise pre-sented to the local power supply rails fromthat of the entire system. Usually local sup-

ply noise appears as common mode noiseat the converter and does not pollute themain system power supply rails.

The isolated positive output can be con-nected to the input ground rail to generate anegative supply rail if required. Since theoutput is isolated from the input, the choiceof reference voltage for the output side canbe arbitrary, for example an additional singlerail can be generated above the main supplyrail, or offset by some other DC value (seefigure 2).

Regulated converters need more considera-tion than the unregulated types for mixingthe reference level. Essentially the singlesupply rail has a regulator in its +VO rail

only, hence referencing the isolated groundwill only work if all the current return isthrough the DC-DC and not via other exter-nal components (e.g. diode bias, resistorfeed). Having an alternative return path canupset the regulation and the performance ofthe system may not equal that of the con-verter.

Isolation Voltage vs. Rated Working VoltageThe isolation voltage given in the datasheetis valid for 1 second flash tested only.If a isolation barrier is required for longer orinfinite time the Rated Working Voltage hasto be used.Conversion of Isolation Voltage to RatedWorking Voltage can be done by using thistable or graph.

DC-DC Converter ApplicationsDC-DC Converter ApplicationsExample: RP30-2405SEW starts deratingwithout heatsink at +65C but the desiredoperation is 30W at +75C so the size ofthe heatsink has to be calculated.

So it has to be ensured that the thermalresistance between case and ambient is6,1C/W max.

When mounting a heatsink on a case thereis a thermal resistance RTH case-heatsink be-tween case and heatsink which can bereduced by using thermal conductivity pastebut cannot be eliminated totally.

Using this value, a suitable heat sink can beselected.

Adding a fan increases the efficiency of anyadditional heat sinking, but adds cost andpower loading.

In most cases choosing the next higherwattage-series and using power-decreas-ing via derating may be the more efficientsolution.

Efficiency = 88% max.P =out 30 W

Tcase = 100 C (max. allowed case temperature)Tambient= 75 C

dP = =PPout

outEfficiency30 W88 %

30 W = 4,1 W

=RTHcase-ambient

dPTcase Tambient = 100 C 75 C = 6,1 C/W

4,1 W

=RTHcase-ambient RTHcase-heat sink + RTHheat sink-ambient

Heatsink mounted on casewithout thermal conductivity paste RTH case-heatsink = ca. 12 C/W

Heatsink mounted on case

with thermal conductivity paste RTH case-heatsink = ca. 0,51 C/WHeatsink mounted on casewith thermal conductivity pasteand electrical-isolation-film RTH case-heatsink = ca. 11,5 C/W

If a heatsink is mounted on the converter its thermal resistance has to be at least:

= =RTHheat sink-ambient RTHcase-ambient RTHcase-heat sink 6,1 C/W 1 C/W = 5,1 C/W

0 1 2 3 4 5 6 7

Rated Working Voltage (kV)

I s o l a t i o n T e s t V o l t a g e ( k V ) 12

10

8

6

4

2

0

Figure 5: IEC950 Test Voltage for Electrical Strength Tests

Table 2: Typical Breakdown Voltage Ratings According to IEC950

Isolation Test Voltage (V) Rated Working Voltage (V)

1000 130

1500 230

3000 1100

6000 3050



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DC-DC Converter ApplicationsDC-DC Converter ApplicationsDC-DC Converter ApplicationsDC-DC Converter ApplicationsThe graph and table above show the requi-rements from IEC950. According to our

experience and in-house-test, we can offerthe following conversion tables:

Isolation Test Voltage Isolation Test Voltage Isolation Test Voltage

(1 second) (1 minute) (1 minute)500 VDC 400 VDC 250 VAC

1000 VDC 800 VDC 500 VAC

1500 VDC 1200 VDC 750 VAC

2000 VDC 1600 VDC 1000 VAC

2500 VDC 2000 VDC 1250 VAC

3000 VDC 2400 VDC 1500 VAC

4000 VDC 3200 VDC 2000 VAC

5000 VDC 4000 VDC 2500 VAC

6000 VDC 4800 VDC 3000 VAC

Table 1 : D.C. Isolation Voltage test vs different conditions

Isolation Test Voltage Isolation Test Voltage Isolation Test Voltage(1 second) (1 minute) (1 minute)

500 VAC 350 VAC 565 VDC

1000 VAC 700 VAC 1130 VDC

1500 VAC 1050 VAC 1695 VDC

2000 VAC 1400 VAC 2260 VDC

2500 VAC 1750 VAC 2825 VDC

3000 VAC 2100 VAC 3390 VDC

4000 VAC 2800 VAC 4520 VDC

5000 VAC 3500 VAC 5650 VDC

6000 VAC 4200 VAC 6780 VDC

Table 2 : A.C. Isolation Voltage test vs different conditions

Isolation mode in IGBT driver circuitsDC/DC converters may be used in driver circuits for IGBT stacks. In these applications, an additional source of stress has to be conside-red. Not only the permanently high isolation voltage requiring a high rated working voltage for the converter is present, but also the highlydynamic switching is a stressing factor - this can reach 20kV/s and more !Taking into account that both factors mean a permanent stress to the converter for all of it's lifetime, it is recommended to overspec theconverter in terms of isolation - i.e. even if a 3kVDC (for 2 second) product seems to fit if you look at just the rated working voltage that isrequired, it still is recommended to choose a product which is specified for 5,2kVDC or 6kVDC (for 1 second) to cover also the high dv/dt.The higher the isolation voltage rating for a DC/DC converter is, the lower the coupling (isolation) capacitance and a low coupling capaci-tance is essential in AC or highly dynamic switched DC usage.This will ensure a safe usage and avoid a shortened lifetime in such a highly demanding situation.



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ConnectingDC-DC Converters in SeriesGalvanic isolation of the output allows mul-tiple converters to be connected in series,

simply by connecting the positive output ofone converter to the negative of another (seefigure 3). In this way non-standard voltagerails can be generated, however, the currentoutput of the highest output voltage conver-ter should not be exceeded.

When converters are connected in series,additional filtering is strongly recommended,as the converters switching circuits are notsynchronised. As well as a summation of theripple voltages, the output could also produ-ce relatively large beat frequencies. A capa-

citor across the output will help, as will aseries inductor (see filtering).

ConnectingDC-DC Converters in ParallelConnecting the outputs of DC/DC convertersin parallel is possible but not recommended.Usually DC/DC converters have no possibili-ty to balance out the output currents. Sothere is potential danger that if the loadingis asymmetrical, that one of the convertersstarts to be overloaded while the others

have to deliver less current. The overloadedconverter may then drop out of circuit lea-ding to power supply oscillation.The only possibility to balance out the indi-vidual currents is to use a special balancefunction (like in R-5xxx) or use converterswith SENSE function and additional load-share-controllers (as can be done for RP40-xxxxSG).


Figure 3: Connecting DC-DC Converters in Series

Figure 4: Paralleled DC-DC Converters with BalanceFunction.

Figure 5: Paralleled DC-DC Converters using Load Share Controllers


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FilteringWhen reducing the ripple from the conver-ter, at either the input or the output, thereare several aspects to be considered.

Recom recommend filtering using simplepassive LC networks at both input and out-put (see figure 6). A passive RC network could be used, however, the power lossthrough a resistor is often too high.The self-resonant frequency of the inductor needs tobe significantly higher than the characteri-stic frequency of the device (typically1OOkHz for Recom DC-DC converters). TheDC current rating of the inductor also needsconsideration, a rating of approximately twicethe supply current is recommended.The DC resistance of the inductor is the finalconsideration that will give an indication ofthe DC power loss to be expected from theinductor.

Output Filtering calculation:Calculating of the filtering components canbe done using

This frequency should be significant lowerthan the switching frequency of the converter.

Example - RC series:Operating frequency = 85kHz max.

fc =10 % of 85 kHz = 8,5 kHz

However, depending on your applicationdesign and loadsituation may interfer withthe calculated filter so testing in the finalapplication and re-adjustment of the com-ponents values may be necessary.

When choosing a value for the filteringcapacitor please take care that the maxi-mum capacitive load is within the specifica-tions of the converter.

Better results in filtering can be achieved ifcommon mode chokes are used instead of asingle choke. Common mode chokes aremultiple chokes sharing a core material sothe common mode rejection (Electrical noisewhich comes through one power line andreturns to the noise source through sometype of ground path is common modenoise.) is higher. Please refer to our page"Common Mode Chokes for EMC" also partof these application notes. These can beused for input filtering as well as for the out-put side.

Limiting Inrush CurrentUsing a series inductor at the input will limitthe current that can be seen at switch on(see figure 7).

If we consider the circuit without the seriesinductor, then the input current is given by;

i = V exp( t )R RCWhen the component is initially switched on(i.e. t=O) this simplifies to;

i = VR

This would imply that for a 5V input, withsay 50mOhm track and wire resistance, theinrush current could be as large as 1OOA.This could cause a problem for the DC-DCconverter.

A series input inductor therefore not only filtersthe noise from the internal switching circuit,but also limits the inrush current at switch on.


Figure 6: Input and Output Filtering

Figure 7: Input Current & Voltage at Switch On

VIN

time

i =V_R

V_R

Voltage : V = Vin (1 exp )( )t__RC

Current : i = exp( )t__RC

C0

1

LOUT=fc

2

C0

1

LOUT=fc

2

C0

1

LOUT2=fc 8,5 kHz =

for:LOUT =470 H

=

=

=

C01 1

(2 f )c2LOUT (2 8,5 kHz)

2470 uH745 nF


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Maximum Output Capacitance

A simple method of reducing the outputripple is simply to add a large external capa-citor. This can be a low cost alternative tothe LC filter approach, although not aseffective. There is also the possibility of cau-sing start up problems, if the output capaci-tance is too large.With a large output capacitance at switchon, there is no charge on the capacitors andthe DC-DC converter immediately experi-ences a large current demand at its output.The inrush current can be so large as toexceed the ability of the DC-DC converter,and the device can go into current limit oran undefined mode of operation. In the

worst case scenario the device continuous-ly "hiccups" as it tries to start, goes intooverload shutdown and then retries again.

The DC-DC converter may not survive if thiscondition persists.

For the Powerline the maximum capacitiveloads are specified. For Econoline please

refer to the tables below.If instead of single capacitors on outputs aL-C-filter is used the max. capacitive laodcan be higher because the choke is preven-ting too high rising speed of the currentpeak. However the achievable max. cap.load is depending on the quality of the filterand the ESR of the capacitors.

Settling TimeThe main reason for not fitting a seriesinductor internally, apart from size con-

straints, is that many applications require afast switch on time. When the input voltageis a fast ramp, then the output can respond

within 500s of the input reaching its targetvoltage (measured on a range of RA/RB andRC/RD converters under full output load wit-hout external filters). The use of external fil-ters and additional input or output capaci-tance will slow this reaction time. It is there-fore left to the designer to decide on thepredominant factors important for their cir-cuit, settling time or noise performance.

Isolation Capacitanceand Leakage CurrentThe isolation barrier within the DC-DC con-verter has a capacitance, which is a mea-sure of the coupling between input and out-put circuits. Providing this is the largestcoupling source, a calculation of the leaka-

ge current between input and output circuitscan be calculated.


Single Output Dual Output

4.7F max.

6.8F max. 3.3F max.

10F max. 6.8F max.

10F max. 6.8F max.

Max. capacitive load for unregulated Econoline models

Unregulated 0.25WUnregulated 0.5W

Unregulated 1WRegulated 0.5WUnregulated 1.25W

Unregulated 1.5W

Unregulated 2WRegulated 1W

Max. capacitive load

3.3V 1000F

5.0V 470F

9.0V 220F

12.0V 120F

15.0V 100F

5.0V 220F

9.0V 100F

12.0V 68F

15.0V 47FMax. capacitive load for REC2.2 series

2.2W

Single output

Dual output


3.3V 2200F

5.0V 1000F

9.0V 470F

12.0V 220F

15.0V 120F

5.0V 470F

9.0V 220F

12.0V 100F

15.0V 68FMax. capacitive load for REC3 and REC5 series

3W , 5W

Single output

Dual output


3.3V 3300F

5.0V 2200F

9.0V 680F

12.0V 330F

15.0V 220F

5.0V 1000F

9.0V 330F

12.0V 160F

15.0V 100FMax. capacitive load for REC7.5 series

7.5W

Single output

Dual output



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Assuming we have a known isolation capa-citance (Cis - refer to datasheet) and a knownfrequency for either the noise or test signal,then the expected leakage current (iL) bet-ween input and output circuits can be calcu-lated from the impedance.The general isolation impedance equationfor a given frequency (f) is given by:

Z f = ___1___ j 2 C is

For an RB-0505D, the isolation ca-pacitan-ce is 18pF, hence the isolation im-pedanceto a 50Hz test signal is:

Z 50 = ___1_______ = 177 M j 2 50 18 pf

If using a test voltage of 1kVrms,the leakage current is:

i L= Vtest= _1000V_ = 5.65 AZ

f177 M

It can be easily observed from these simpleequations that the higher the test or noisevoltage, the larger the leakage current, alsothe lower the isolation capacitance, the lowerthe leakage current. Hence for low leakagecurrent, high noise immunity designs, high

isolation DC-DC converters should be selectedwith an appropriate low isolation capacitance.

Application Examples

Overload Protection Although the use of filtering will preventexcessive current at power-on under normaloperating conditions, many of the lower costconverters have no protection against anoutput circuit taking excessive power oreven going short-circuit. When this hap-

pens, the DC-DC converter will take a largeinput current to try to supply the output.Eventually the converter will overheat anddestroy itself if this condition is not rectified(short circuit overload is only guaranteed for1 s on an unregulated part).

There are several ways to prevent overloadat the outputs destroying the DC-DC conver-ter. The simplest being a straight forwardfuse. Sufficient tolerance for inrush currentis required to ensure the fuse does not blowon power-on (see figure 8). Another simple

scheme that can be applied is a circuitbreaker.There is also the potential to add some in-telligence to the overload scheme by either

detecting the input current, or the outputvoltage (see figure 9).If there is an intelligent power managementsystem at the input, using a series resistor(in place of the series inductor) and detec-ting the voltage drop across the device tosignal the management system can beused. A similar scheme can be used at theoutput to determine the output voltage,however, if the management system is onthe input side, the signal will need to be iso-lated from the controller to preserve thesystem isolation barrier (see figure 10).There are several other current limitingtechniques that can be used to detect anoverload situation, the suitability of these isleft to the designer. The most important

thing to consider is how this information will beused. If the system needs to signal to a control-ler the location or module causing the overload,some form of intelligence will be needed. Ifthe device simply needs to switch off, a sim-ple fuse type arrangement will be adequate.

Unregulated RECOM DC/DC converters usu-ally are short circuit protected only for ashort time like 1 second. By option they canbe continous short circuit protected (option

/P), then their design is able to withstand thehigh output current at overload situation wit-hout any need for extra circuit protection. AllRecom DC-DC converters which include aninternal linear regulator have a thermal over-load shut-down condition which protectsthese devices from excessive over-load. Ifthis condition is to be used to inform apower management system, the most sui-table arrangement is the output voltagedetector (see figure 10a), since this will fallto near zero on shut-down. Wide input rangeregulated converters offer overload protecti-

on / short circuit protection via an internalcircuit that interfers with the primary oscilla-tor so the switching is regulated back insituations of overload or output short circuit.

DC-DC Converter ApplicationsDC-DC Converter ApplicationsDC-DC Converter ApplicationsDC-DC Converter Applications

DC

DC

GND

FuseVIN

Figure 8: Simple Overload Protection

DC

DC

DC

DCVCC

RIN

VOL

GND

GND

VCC ILIMIT

RGND

R1

R2

Figure 9: Input Monitored Overload Protection

a) Series Resistor for Input Current Measurement

b) Ground Current Monitor

Choose current limit (ILIMIT)and ground resistor (RGND) sothat : 0.7V = RGND x ILIMIT.



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Input VoltageDrop-Out (brown-outs)When the input voltage drops, or is mo-mentarily removed, the output circuit wouldsuffer similar voltage drops. For short pe-riod input voltage drops, such as when otherconnected circuits have an instantaneouscurrent demand, or devices are plugged in orremoved from the supply rail while 'hot', asimple diode-capacitor arrangement can pre-vent the output circuit from being effected.The circuit uses a diode feed to a largereservoir capacitor (typically 47F electroly-tic), which provides a short term reservecurrent source for the converter, the diodeblocking other circuits from draining thecapacitor over the supply rail. When combi-ned with an in-line inductor this can also beused to give very good filtering. The diodevolt drop needs to be considered in thepower supply line under normal supply con-ditions. A low drop Schottky diode is recom-mended (see figure 11).

No Load Over Voltage Lock-OutUnregulated DC-DC converters are expectedto be under a minimum of 10% load, hence

below this load level the output voltage isundefined. In certain circuits this could be apotential problem.The easiest way to ensure the output volta-ge remains within a specified tolerance, is toadd external resistors, so that there isalways a minimum 10% loading on thedevice (see figure 12). This is rather ineffi-cient in that 10% of the power is alwaysbeing taken by this load, hence only 90% isavailable to the additional circuitry.Zener diodes on the output are another sim-

ple method. It is recommended that thesebe used with a series resistor or inductor, aswhen the Zener action occurs, a large cur-rent surge may induce signal noise into thesystem.


Figure 10 : Ouput Monitored Overload Protection

DC

DC

VCC

GND

+VO

OV

RD

VOL

RO Opto-Isolator

Opto-Isolated Overload Detector(On overload +VO falls and the LED switches off, the VOL. line is then pulled high.)

DC

DC47F

LINZDX60

Output Circuit

Figure 11 : Input Voltage Drop-out

R2

DC

DC

R10%

DC

DC

R10%

Figure 12: No Load over Voltage Lock-Out



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Long Distance Supply LinesWhen the supply is transmitted via a cable,there are several reasons why using an iso-lated DC-DC converter is good design prac-

tice (see figure 13). The noise pick up andEMC susceptibility of a cable is high compa-red to a pcb track. By isolating the cable viaa DC-DC converter at either end, any cablepick-up will appear as common mode noiseand should be self-cancelling at the conver-ters.

Another reason is to reduce the cable lossby using a high voltage, low current powertransfer through the cable and reconverting

at the terminating circuit. This will also redu-ce noise and EMC susceptibility, since thenoise voltage required to affect the rail isalso raised.For example, compare a system having a 5Vsupply and requiring a 5V, 500mW output ata remote circuit. Assume the connectingcable has a 100 Ohm resistance. Using anRN-0505 to convert the power at either endof the cable, with a 100mA current, thecable will lose 1W (I2R) of power.The RO/RN would not be suitable, since thisis its total power delivery; hence there is nopower available for the terminating circuit.Using a RB-0512D to generate 24V and aRA-2405D to regenerate 5V, only a 21 mA

supply is required through the cable, a cableloss of 44mW.

LCD Display Bias A LCD display typically requires a positive ornegative 24V supply to bias the crystal. TheRO-0524S converter was designed specifi-cally for this application. Having an isolatedOV output, this device can be configured asa +24V supply by connecting this to theGND input, or a 24V supply by connectingthe +Vo output to GND (see figure 14).

EIA-232 Interface

In a mains powered PC often several sup-ply rails are available to power a RS232interface. However, battery operated PCs orremote equipment having a RS232 inter-face added later, or as an option, may nothave the supply rails to power a RS232interface. Using a RB-0512S is a simplesingle chip solution, allowing a fully EIA-232compatible interface to be implementedfrom a single 5V supply rail, and only 2additional components (see figure 15).

3V/5V Logic Mixed Supply Rails

There has been a lot of attention given tonew l.C.'s and logic functions operating atwhat is rapidly emerging as the standardsupply level for notebook and palmtop com-puters. The 3.3V supply is also gaining rapidacceptance as the defacto standard for per-sonal telecommunications, however, not allcircuit functions required are currently avai-lable in a 3.3V powered IC. The system desi-gner therefore has previously had only twooptions available; use standard 5V logic orwait until the required parts are available ina 3V form, neither being entirely satisfac-tory and the latter possibly resulting in lostmarket share.

There is now another option, mixed logicfunctions running from separate supplyrails. A single 3.3V line can be combinedwith a range of DC-DC converters fromRecom, to generate voltage levels to run vir-tually any standard logic or interface IC.The Recom range includes dual output partsfor powering analogue bipolar and amplifierfunctions (RA/RB series), as well a singleoutput function for localised logic functions(RL/RM, RN/RO series). A typical examplemight be a RS232 interface circuit in a lap-

top PC using a 3.3V interface chip (such asthe LT1330), which accepts 3.3V logicsignals but requires a 5V supply (see figure16). Recom has another variation on thistheme and has developed two 5V to 3.3Vstep down DC-DC converters (RL-053.3 andR0-053.3). These have been designed toallow existing systems to start incorpora-ting available 3.3V l.C.'s without having toredesign their power supply.This is particularly important when trying toreduce the overall power demand of asystem, but not having available all of thefunctions at the 3.3V supply.The main application for this range of de-vices are system designers, who want toprovide some functionality that requires ahigher voltage than is available from thesupply rail, or for a single localised function.Using a fully isolated supply is particularlyuseful in interface functions and systemsmaintaining separate analogue and digitalground lines.

DC-DC Converter ApplicationsDC-DC Converter ApplicationsDC-DC Converter ApplicationsDC-DC Converter Applications

Figure 13: Long Distance Power Transfer

Figure 14: LCD Display Bias



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Isolated Data Acquisition System Any active system requiring isolation willneed a DC-DC converter to provide thepower transfer for the isolated circuit. In adata acquisition circuit there is also the needfor low noise on the supply line; hence goodfiltering is required.The circuit shown (see figure 17) provides avery high isolation barrier by using anRG/RH/RJ/RK converter; to provide thepower isolation and SFH610 opto-isolatorsfor the data isolation. An overall system iso-lation of 2.5kV is achieved.

EMC ConsiderationsWhen used for isolating a local power sup-ply and incorporating the appropriate filtercircuits as illustrated in Fig. 17), DC-DC con-verters can present simple elegant solutionsto many EMC power supply problems. Therange of fixed frequency DC-DC convertersis particularly suitable for use in EMC pro-blem situations, as the stable fixed switchingfrequency gives easily characterised andeasily filtered output.The following notes give suggestions toavoid common EMC problems in power sup-ply circuits.


Figure 15: Optimised RS232 Interface

Figure 16: RS232 Interface with 3V Logic



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Figure 17: Isolated Serial ADC System

CCT1 CCT2

GND

VCC

Figure 18: Eliminate Loops in Supply Line

Figure 19: Decouple Supply Lines at Local Boundaries

Power Supply Considerations Eliminate loops in supply lines (see figure 18). Decouple supply lines at local boundaries (use RCL fitters withlow Q, see figure 19). Place high speed sections close to the power line input, slo-west section furthest away (reduces power plane transients, seefigure 20). Isolate individual systems where possible (especially analogueand digital systems) on both power supply and signal lines (seefigure 21).

An isolated DC-DC converter can provide a significant benefit tohelp reduce susceptibility and conducted emission due to the iso-lation of both power rail and ground from the sys-tem supply. Therange of DC-DC converters available from Recom all utilise toroi-dal power transformers and as such have negligible EMI.Isolated DC-DC converters are switching devices and as suchhave a characteristic switching frequency, which may need someadditional filtering.

Interpretation of DC-DC Converter EMC Data

Electromagnetic compatibility (EMC) of elec-trical and electronicproducts is a measure of electrical pollution. Throughout the worldthere are increasing statutory and regulatory requirements todemonstrate the EMC of end products. In Europe the EC directive89/336/EEC requires that, any product sold after 1 January 1996complies with a series of EMC limits, otherwise the product will beprohibited from sale within the EEC and the seller could be prose-cuted and fined.

Although DC-DC converters are generally exempt from EMC regu-lations on the grounds that these are component items, it is thebelief of Recom that the information on the EMC of these compo-nents can help designers ensure their end product can meet therelevant statutory EMC requirements. It must be rememberedhowever, that the DC-DC converter is unlikely to be the last com-ponent in the chain to the mains supply, hence the informationquoted needs interpretation by the circuit designer to deter-mineits impact on the final EMC of their system.



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The notes given here are aimed at helpingthe designer interpret the effect the DC-DCconverter will have on the EMC of their endproduct, by describing the methods andrationale for the measurements made.Where possible CISPR and EN standardshave been used to determine the noisespectra of the components, however, all of

the standards reference to mains poweredequipment and interpretation of these spe-cifications is necessary to examine DC sup-plied devices.

Conducted andRadiated Emissions

There are basically two types of emissionscovered by the EC directive on EMC, radi-ated and conducted. Conducted emissionsare those transmitted over wire connectingcircuits together and covers the frequency

spectrum 150kHz to 30MHz. Radiated arethose emissions transmitted via electromag-netic waves in air and cover the frequencyspectrum 30MHz to 1GHz. Hence the EC

directive covers the frequency spectrum150kHz to 1GHz, but as two separate anddistinct modes of transmission.The Recom range of DC-DC converters fea-

ture toroidal transformers. These have beentested and proved to have negligible radia-ted noise. The low radiated noise is primari-ly due to toroidal shaped transformers main-taining the mag-netic flux within the core,hence no magnetic flux is radiated bydesign. Due to the exceptionally low value ofradiated emis-sion, only conducted emissi-ons are quoted.Conducted emissions are measured on theinput DC supply line. Unfortunately no stan-dards exist for DC supplies, as most stan-dards cover mains connected equipment.This poses two problems for a DC supplieddevice, firstly no standard limit lines can bedirectly applied, since the DC supplied devi-ce does not directly connect to the mains,also all reference material uses the earth-ground plane as reference point. In a DCsystem often the OV is the reference, how-ever, for EMC purposes, it is probably moreeffective to maintain the earth as the refe-rence, since this is likely to be the referencethat the shielding or casing is connected to.Consequently all measurements quoted are

referenced to the mains borne earth.

Line ImpedanceStabilisation Network (LISN)It is necessary to ensure that any measure-ment of noise is from the device under test(DUT) and not from the supply to this device.In mains connected circuits this is im-por-tant and the mains has to be filtered prior tosupply to the DUT. The same approach hasbeen used in the testing of DC-DC conver-ters and the DC supply to the converter was

filtered, to ensure that no noise from thePSU as present at the measuring instru-ment.

A line impedance stabilisation network (LISN) conforming to CISPR 16 specifica-tion is connected to both positive and ne-gative supply rails and referenced to mainsearth (see figure 22). The measurementsare all taken from the positive supply rail,with the negative rail measurement pointterminated with 50 Ohm to impedancematch the measurement channels.


Figure 20: Place High Spead Circuit Close to PSU

Figure 21 : Isolate Individual Systems

+

LISN

LISN

DCDC

To Spectrum Analyser

Power Supply50

Termination

Load

Figure 22: Filtered Supply to DC-DC Converter



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Shielding At all times the DUT, LlSN's and all cablesconnecting any measurement equipment,loads and supply lines are shielded. Theshielding is to prevent possible pick-up oncables and DUT from external EMC sources(e.g. other equipment close by). The shiel-ding is referenced to mains earth (see figu-re 22).

Line Spectra of DC-DC Converters All DC-DC converters are switching devices,hence, will have a frequency spectra. Fixedinput DC-DC converters have fixed swit-ching frequency, for example the RC/RDrange of converters has a typical switchingfrequency of 50kHz. This gives a stable andpredictable noise spectrum regardless of

load conditions.If we examine the noise spectrum closely(see figure 23) we can see several distinctpeaks, these arise from the fundamental

switching frequency and its harmonics (oddline spectra) and the full rectified spectra, attwice the fundamental switching frequency(even line spectra). Quasi-resonant conver-ters, such as the Recom range, have squa-re wave switching waveforms, this produceslower ripple and a higher efficiency thansoft switching devices, but has the draw-back of having a relatively large spectrum ofharmonics.

The EC regulations for conducted interfer-ence covers the bandwidth 150kHz to30MHz. Considering a converter with a100kHz nominal switching frequency, thiswould exhibit 299 individual line spectra.There will also be a variation of absoluteswitching frequency with production varia-

tion, hence a part with a 90kHz nominal fre-quency would have an additional 33 linesover the entire 30MHz bandwidth. Absoluteinput voltage also produces slight variationof switching frequency (see figure 24). Hence,to give a general level of conducted noise,we have used a 100kHz resolution band-width (RBW) to examine the spectra in thedata sheets. This wide RBW gives a maxi-mum level over all the peaks, rather than theindividual line spectra. This is easier to readas well as automatically compensating for

variances in switching frequency due to pro-duction variation or differences in absoluteinput voltage (see figure 25).The conducted emissions are measuredunder full load conditions in all cases. Underlower loads the emission levels do fall,hence full load is the worst case conditionfor conducted line noise.

Temperature Performanceof DC-DC ConvertersThe temperature performance of the DC-DC

converters detailed in this book is alwaysbetter than the quoted operating tempera-ture range. The main reason for being con-servative on the operating temperaturerange is the difficulty of accurately specify-ing parametric performance outside thistemperature range.There are some limiting factors which provi-de physical barriers to performance, such asthe Curie temperature of the core materialused in the DC-DC converter (the lowestCurie temperature material in use at Recomis 125C). Ceramic capacitors are usedalmost exclusively in the DC-DC convertersbecause of their high reliability and exten-ded life properties, however, the absolute


Figure 23: Individual Line Spectra

Figure 24: Frequency Voltage Dependency

Figure 25 : V Spectrum

0

1

2

3

4

5

6

7

8

9

10

11

12

13

100

Frequency (kHz)

100

80

60

40

20

0

Frequency

C o n d u c t e d E m i s s i o n ( d B u V )

100

80

60

40

20

100kHz 1MHz 10MHz 100MHz0 C

o n d u c t e d E m i s s i o n ( d B u V )

200 300 400 500



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capacity of these can fall when the tempe-rature rises above 85C (ripple will increa-se). Other considerations are the power dis-sipation within the active switching compo-nents, although these have a very high tem-perature rating. Their current carrying capa-city derates as temperature exceeds 100C.Therefore this allows the DC-DC convertersto be used above their specified operatingtemperature, providing the derating of powerdelivery given in the specification is adheredto. Components operating outside the quotedoperating temperature range cannot be ex-pected to exhibit the same parametric per-formance that is quoted in the specification.

An indication of the stability of a device can

be obtained from the change in its operatingfrequency, as the temperature is varied (seefigure 26). A typical value for the frequencyvariation with temperature is 0.5% per C, avery low value compared to other commer-cial parts. This illustrates the ease of filteringof Recom DC-DC converters, since the fre-quency is so stable across load and tempe-rature ranges.

Transfer Moulded(SMD) DC-DC Converters

Production Guideline Application Note

The introduction by Recom of a new andinnovative method of encapsulating hybridDC-DC converters in a transfer moulded(TM) epoxy molding compound plastic hasenabled a new range of surface mount(SMD) DC-DC converters to be brought tomarket, which addresses the componentplacement with SOIC style handling.With any new component there are of coursenew lessons to be learned with the moun-

ting technology. With the Recom SMD DC-DC converters, the lessons are not new assuch, but may require different productiontechniques in certain applications.

Component MaterialsRecom SMD converters are manufactured ina slightly different way than the through-hole converters. Instead of potting the PCBboard inside a plastic case with conventio-nal epoxy the whole package is moldedaround the PCB board with epoxy moldingcompound plastic. This ensures better ther-mal conductivity from the heat generatingcomponents like semiconductors, transfor-mer, etc. inside to the surface from where itcan dissipate via convection. This makesthem ideal for reflow processes also underthe stricter conditions of lead-free solderingtemperatures that meet the requirements ofthe ROHS regulation.

All materials used in RECOM lead-free pro-ducts are ROHS compliant, thus the totalamount of the restricted materials (lead,mercury, cadmium, hexavalent chromium,PBBs and PBDEs) are below the prescribedlimits. Detailed chemical analysis reportsare available.

Component PlacementRecom SMD DC-DC converters are desi-gned to be handled by placement machines

in a similar way to standard SOIC packages.The parts are available either in tubes(sticks) or in reels. The parts can thereforebe placed using machines with either vibra-tional shuttle, gravity feeders, or reel fee-ders.The vacuum nozzle for picking and pla-cing the components can be the same asused for a standard 14 pin or 18 pin SOIC(typically a 5mm diameter nozzle). Anincrease in vacuum pressure may be bene-ficial, due to the heavier weight of the hybridcompared to a standard SOIC part (a typical14 pin SOIC weighs 0.1g, the Recom SMDDC-DC converter weighs 1.5 ~ 2,7g). It isadvisable to consult your machine supplieron the best choice of vacuum nozzle if indoubt. If placing these components by hand,

handle the components only by the centralbody area where there are no componentpins.

Component AlignmentThe components can be aligned by eitheroptical recognition or manual alignment. Ifusing manual alignment it should be ensu-red that the tweezers press on the compo-nent body and not on the pins. The compo-nents themselves are symmetrical alongtheir axis, hence relatively easy to alignusing either method.

Solder Pad DesignThe Recom SMD DC-DC converters aredesigned on a pin pitch of 2,54mm (0.1")with 1,20mm pad widths and 1,80mm padlengths.

This allows pads from one part to be usedwithin a PCB CAD package for forming the

pad layouts for other SMD converters. Thesepads are wider than many standard SOICpad sizes (0.64mm) and CAD packages maynot accommodate these pins with a stan-dard SOIC pad pattern. It should be remem-bered that these components are powersupply devices and as such need widerpads and thicker component leads to mini-mise resistive losses within the intercon-nects.

Solder Reflow Profile

RECOM's SMD converters are designed towithstand a maximum reflow temperature of245C (for max. 30seconds) in accordancewith JEDEC STD-020C. If multiple reflowprofiles are to be used (i.e. the part is to passthrough several reflow ovens), it is recom-mended that lower ramp rates be used thanthe maximum specified in JEDEC STD-020C. Continual thermal cycling to this pro-file could cause material fatigue, if morethan 5 maximum ramp cycles are used.In general these parts will exceed the re-

flow capability of most IC and passive com-ponents on a PCB and should prove themost thermally insensitive component to thereflow conditions.


160

140

120

100

80

60 S w i t c h i n g F r e q u

e n c y ( k H z )

20 0 20 40 60 80 100

Temperature ( C)

O/N

A/B

C/D

Under Full Load Conditions

Figure 26: Typical Switching Frequency vs. Temperature



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Recommended Solder Reflow Profile:

The following 2 graphs show the typicalrecommended solder reflow profiles forSMD and through-hole ROHS compliantconverters.

The exact values of the profiles peak andits maximum allowed duration is also givenin the datasheet of each converter.

Adhesive Requirements

If SM surface mount components are goingto be wave soldered (i.e. in a mixed throughhole and SMD PCB) or are to be mounted onboth sides of a PCB, then it is necessary touse an adhesive to fix them to the board

prior to reflow. The adhesive prevents theSMD parts being 'washed off' in a wave sol-der, and being 'vibrated off' due to handlingon a double sided SMD board.

As mentioned previously, the Recom rangeof SMD DC-DC converters are heavier thanstandard SOIC devices. The heavier weightis a due to their size (volume) and internalhybrid construction. Consequently the partsplace a larger than usual stress on their sol-der joints and leads if these are the onlymethod of attachment. Using an adhesive

between component body and PCB canreduce this stress considerably. If the finalsystem is to be subjected to shock and vibra-tion testing, then using adhesive attachment

is essential to ensure the parts pass theseenvironmental tests.The Recom SMD DC-DC converters all havea stand-off beneath the component for theapplication of adhesive to be placed, withoutinterfering with the siting of the component.The method of adhesive dispensing andcuring, plus requirements for environmentaltest and in-service replacement will deter-mine suitability of adhesives rather than thecomponent itself. However, having a ther-moset plastic body, thermoset epoxy adhesi-ve bonding between board and componentis the recommended adhesive chemistry.If the reflow stage is also to be used as acure for a heat cure adhesive, then the com-ponent is likely to undergo high horizontal

acceleration and deceleration during thepick and place operation. The adhesive mustbe sufficiently strong in its uncured (green)state, in order to keep the component accu-rately placed.

Adhesive PlacementThe parts are fully compatible with the 3main methods of adhesive dispensing; pintransfer, printing and dispensing. Themethod of placing adhesive will depend onthe available processes in the production

line and the reason for using adhesiveattachment. For example, if the part is on amixed though-hole and SMD board, adhesi-ve will have to be placed and cured prior toreflow. If using a SMD only board and heatcure adhesive, the reflow may be used asthe cure stage. If requiring adhesive forshock and vibration, but using a conformalcoat, then it may be possible to avoid aseparate adhesive alltogether, and thecoating alone provides the mechanicalrestraint on the component body.Patterns for dispensing or printing adhesiveare given for automatic lines. If dispensingmanually after placement the patterns forUV cure are easily repeated using a manualsyringe (even if using heat cure adhesive).Ifdispensing manually, dot height and size arenot as important, and the ad-hesive shouldbe applied after the components have beenreflowed. When dispensing after reflow, achip underfill formulation adhesive would bethe preferred choice. These types 'wick' underthe component body and offer a good allround adhesion from a single dispensed dot.

The patterns allow for the process spread ofthe stand-off on the component, but do notaccount for the thickness of the PCB tracks.




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DC-DC Converter ApplicationsDC-DC Converter ApplicationsIf thick PCB tracks are to be used, a groun-ded copper strip should be laid beneath thecentre of the component (care should beexercised to maintain isolation barrierlimits). The adhesive should not retard thepins reaching their solder pads during pla-cement of the part, hence low viscosityadhesive is recommended.The height of the adhesive dot, its viscosityand slumping properties are critical. The dotmust be high enough to bridge the gap be-tween board surface and component, butlow enough not to slump and spread, or besqueezed by the component, and so conta-minate the solder pads.If wishing to use a greater number of dots ofsmaller diameter (common for pin transfer

methods), the dot pattern can be changed,by following a few simple guidelines. As thenumber of dots is doubled their diametershould be halved and centres should be atleast twice the printed diameter from eachother, but the dot height should re-main at0.4mm. The printed dot should always bepositioned by at least its diameter from thenearest edge of the body to the edge of thedot. The number of dots is not important,provided good contact between adhesiveand body can be guaranteed, but a mini-

mum of 2 is recommended.

CleaningThe thermoset plastic encapsulating ma-terial used for the Recom range of surfacemount DC-DC converters is not fully herme-tically sealed. As with all plastic encapsu-lated active devices, strongly reactiveagents in hostile environments can attack

the material and the internal parts, hencecleaning is recommended in inert solutions(e.g. alcohol or water based solvents) and atroom temperature in an inert atmospheres(e.g. air or nitrogen).

A batch or linear aqueous cleaning processwould be the preferred method of cleaningusing a deionised water solution.

Vapour Phase Reflow SolderingVapour phase soldering is a still upcomingsoldering practice; therefore there are nostandard temperature profiles available.Principally, the Lead-free Soldering Profilerecommended by RECOM can be used forvapour phase soldering. RECOM has testedlarge quantities of 8-pin and 10-pin SMDconverters and recommends as an absolutemaximum condition 240C for 90s dwelltime. In standard applications with smallsized components on a pcb, 230C andshorter dwell times will still deliver goodresults. After discussions with various con-tract manufacturers, we recommended thatthe temperature gradients used during pre-heat and cooling phases are between 0.5K/s up to 3 K/s.Other form factors than 8-pin or 10-pinSMD-packages have not been tested undervapour phase conditions. Please contactRECOM in this case.

Custom DC-DC ConvertersIn addition to the standard ranges shown inthis data book, Recom have the capability toproduce custom DC-DC converters designed toyour specific requirements. In general, the parts

can be rapidly designed using computer bas-ed CAD tools to meet any input or outputvoltage requirements within the ranges ofRecom standard products (i.e. up to 48V ateither input or output). Prototype samplescan also be produced in short timescales.Custom parts can be designed to your spe-cification, or where the part fits within astandard series, the generic series specifi-cation can be used. All custom parts re-ceive the same stringent testing, inspectionand quality procedures, as standard pro-ducts. However there is a minimum orderquantity as this additional documentationsand administrative tasks must be covered interms of costs. A general figure for this MOQcan be around 3000pcs of low wattage con-

verters (0,25pcs ~ 2W), 1000pcs mediumsized wattage (2W~15W) and 500pcs forhigher wattages (> 20W).Recom customparts are used in many applications, whichare very specific to the individual customer,however, some typical examples are:

ECL Logic driver

Multiple cell battery configurations

Telecommunications line equipment

Marine apparatus

Automotive electronics LCD display power circuitry

Board level instrumentation systems

To discuss your custom DC-DC converterrequirements, please contact Recom techni-cal support desk or your local distributor.



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Unregulated Single OutputRM, RL, RQS, RO, RE, ROM, RSS,RB-xxxxS, RA-xxxxS, RBM-xxxxS,RK, RP-xxxxS, RxxPxxS,RxxP2xxS, RN,RTS, RI, REZ, RKZ-xxxxS, RV-xxxxS, RAA-xxxxS, RGZ

Unregulated Dual OutputRQD, RSD, RB-xxxxD, RA-xxxxD,RBM-xxxxD, RH, RP-xxxxD,RxxPxxD, RxxP2xxD, RTD, RC-xxxxD, RD-xxxxD, RKZ-xxxxD, RV-xxxxD, RAA-xxxxD, RJZ

Unregulated Dual Isolated OutputRU, RUZ

Post Regulated Single OutputRZ, RSZ (P), RY-xxxxS, RX-xxxxS, RY-SCP, REC1.5-xxxxSR/H1, REC1.8-xxxxSR/H1, REC2.2-xxxxSR/H1, REC3-xxxxSR/H1

Post Regulated Dual OutputRY-xxxxS, RX-xxxxS, RY-DCP, REC2.2-xxxxDR/H1, REC3-xxxxDR/H1

Block diagramsBlock diagrams



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Block diagramsBlock diagramsRegulated Single OutputRSO, RS, REC2.2-xxxxSRW, RW-xxxxS, REC3-xxxxSRW(Z)/H*, REC5-xxxxSRW(Z)/H*, REC7.5-xxxxSRW/AM/H*, REC10-xxxxSRW(Z)/H, REC15-xxxxSRW(Z)/H, REC20-xxxxSRWB(Z)/H, REC30-xx( 12,15, 24V )SRWZ/H, REC40-xx( 12,15, 24V )SRW/H, REC40-xx( 12,15, 24V )SRWB/H

Regulated Dual OutputRSO-xxxxD, RS-xxxxD, REC2.2-xxxxDRW, RW-xxxxD, REC3-xxxxDRW(Z)/H*, REC5-xxxxDRW(Z)/H*, REC7.5-xxxxDRW/AM/H*,REC10-xxxxDRW(Z)/H, REC15-xxxxDRW(Z)/H, REC20-xxxxDRWB(Z)/H, REC30-xxxxDRWZ/H, REC40-xxxxDRWB/H

Regulated Dual Isolated OutputREC3-DRWI



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Block diagramsBlock diagramsRegulated Single OutputREC20-xxxxSRW/H,REC30-xx( 1.8,2.5, 3.3, 5V )SRWZ/H, REC40-xx( 1.8,2.5, 3.3, 5V )SRW/H, REC40-xx( 1.8,2.5, 3.3, 5V )SRWB/H



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Powerline Definitions and TestingPowerline Definitions and Testing

General Test Set-Up

Note: If the converter is under test withremote sense pins, connect these pins

to their respective output pins. All testsare made in "Local sensing" mode.

Figure 1-3: General DC/DC converter test set-up

Make and record the following measure-ments with rated output load at +25C: Output voltage at nominal line

(input) voltage. V out N Output voltage at high line (input)

voltage. V out H Output voltage at low line (input)

voltage. V out L

The line regulation is Vout M (the maxi-mum of the two deviations of output)for the value at nominal input in per-centage.

V out

M V out

N

V out NX100

Line Regulations

The minimum and maximum input vol-tage limits within which a converter

will operate to specifications.

An input filter, consisting of two capa-citors, is connected in paralell with aseries inductor to reduce input reflec-ted ripple current.

Input Voltage Range

PI Filter

Output Voltage Accuracy

Figure 2: PI Filter

With nominal input voltage and ratedoutput load from the test set-up, theDC output voltage is measured with anaccurate, calibrated DC voltmeter.Output voltage accuracy is the diffe-rence between the measured outputvoltage and specified nominal value asa percentage. Output accuracy (as a %)is then derived by the formula:

Vnom ist the nominal, output specified in the conver-ter data sheet.

V out V nom

V nom NX100

For a multiple output power converter,the percentage difference in the volta-

ge level of two outputs with oppositepolarrities and equal nominal values.

Voltage Balance



24/37


25/37


Figure 4 shows a complex ripple voltagewaveform that may be present on theoutput of a switching power supply.There are three components in thewaveform, first is a charging compo-nent that originates from the outputrectifier and filter, then there is thedischarging component due to the loaddischarging the output capacitor bet-ween cycles, and finally there aresmall high frequency switching spikesimposed on the low frequency ripple.

Figure 4: Amplitude

Output Ripple and Noise (continued)

Transient Recovery Time

Current Limiting

Fold Back Current Limiting

The time required for the power supplyoutput voltage to return to within a spe-cified percentage of rated value, follow-ing a step change in load current.

output current is limited to preventdamage of the converter at overload

situations.

at short circuited outputs the outputvoltage is regulated down so the cur-

rent on outputs cannot be excessive.

A method of protecting a power supplyfrom damage in an overload condition,reducing the output current as the loadapproaches short circuit.

Figure 6: Fold Back Current LimitingTime

Figure: 5 Transient Recovery Time



26/37

Powerline Definitions and TestingPowerline Definitions and TestingThe electrical separation between theinput and output of a converter, (consis-ting of resistive and capacitive isola-

tion) normally determined by transfor-mer characteristics and circuit spacing.

The maximum continuous DC voltage,which may be applied between theinput and output terminal of a powersupply without causing damage.Typical break-down voltage for DC-DCconverters is 500VDC minimum.

With the power converter in a tempera-ture test chamber with rated outputload, make the following measurements: Output voltage at +25C ambient

temperature. Set the chamber for maximum

operating ambient temperatureand allow the power converter tostabilize for 15 to 30 minutes.Measure the output voltage.

Set the chamber to minimumoperating ambient temperature and

allow the power converter to stabi-lize for 15 to 30 minutes.

Divide each percentage voltagedeviation from the +25C ambientvalue by the corresponding tempe-rature change from +25Cambient.

The temperature coefficient is the hig-her one of the two values calculatedabove, expressed as percent perchange centigrade.

Isolation

Break-Down Voltage

Temperature Coefficient

Ambient Temperature

Operating Temperature Range

Storage Temperature Range

Figure 7:

The temperature of the still-air im-

mediately surrouding an operatingpower supply.

The range of ambient or case tem-perature within a power supply at

which it operates safely and meetsits specifications.

The range of ambient temperatureswithin a power supply at non-ope-

rating condition, with no degrada-tion in its subsequent operation.



27/37


Some converters from our Powerlineoffer the feature of trimming the outputvoltage in a certain range around the

nominal value by using external trimresistors.Because different series use differentcircuits for trimming no general equati-on can be given for calculating the

trim-resistors. Following trim-tablesgive values for chosing these trimresistors. If voltages between the given

trim-points are required a linear appro-ximation of the next points is possibleor using trimmable resitors may beconsidered.

Output Voltage Trimming:

Trim up 1 2 3 4 5 6 7 8 9 10 %Vout = 1,818 1,836 1,854 1,872 1,89 1,908 1,926 1,944 1,962 1,98 VoltsRU = 11,88 5,26 3,09 2,00 1,35 0,92 0,61 0,38 0,20 0,06 KOhms

Trim down 1 2 3 4 5 6 7 8 9 10 %Vout = 1,782 1,764 1,746 1,728 1,71 1,692 1,674 1,656 1,638 1,62 VoltsRD = 14,38 6,50 3,84 2,51 1,71 1,17 0,79 0,50 0,27 0,10 KOhms

RP20-, RP30- XX1.8S

Trim up 1 2 3 4 5 6 7 8 9 10 %Vout = 2,525 2,55 2,575 2,6 2,625 2,65 2,675 2,7 2,725 2,75 VoltsRU = 36,65 16,57 9,83 6 ,45 4 ,42 3 ,06 2 ,09 1 ,37 0 ,80 0 ,35 KOhms


RP20-, RP30- XX2.5S



RP15-, RP20-, RP30-, RP40- xx3.3SRP40-, xx3.305T (Trim for +3.3V)



RP15-, RP20-, RP30-, RP40-(Trim for +5V)



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Trim up 1 2 3 4 5 6 7 8 9 10 %Vout = 10,1 10,2 10,3 10,4 10,5 10,6 10,7 10,8 10,9 11 VoltsRU = 90,50 40,65 24,06 15,76 10,79 7,47 5,10 3,33 1,95 0,84 KOhms

Trim down 1 2 3 4 5 6 7 8 9 10 %Vout = 9,9 9,8 9,7 9,6 9,5 9,4 9,3 9,2 9,1 9 VoltsRD = 109,06 48,94 28,87 18,83 12,81 8,79 5,92 3,77 2,10 0,76 KOhms

RP15-, RP20- xx05D



RP15-, RP20-, RP30-, RP40-



RP15-, RP20, RP30-



RP15-, RP20-, RP30-, RP40-

Trim up 1 2 3 4 5 6 7 8 9 10 %Vout = 30,3 30,6 30,9 31,2 31,5 31,8 32,1 32,4 32,7 33 VoltsRU = 306,24 129,65 75,39 49,05 33,49 23,21 15,92 10,48 6,26 2,90 KOhms

Trim down 1 2 3 4 5 6 7 8 9 10 %

Vout = 29,7 29,4 29,1 28,8 28,5 28,2 27,9 27,6 27,3 27 VoltsRD = 300,42 142,30 85,77 56,73 39,05 27,16 18,60 12,16 7,13 3,10 KOhms

RP15-, RP20-, RP30-



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7G-0020A (9.5C/W)

7G-0026A (7.8C/W)

Powerline - Heat SinksPowerline - Heat Sinks



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7G-0011A (8.24C/W)

Powerline - Heat SinksPowerline - Heat Sinks

7G-0022A (INNOLINE)



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No. Types

1. RO, RM, RE, ROM, RB, RBM, RK, RH, RP, RU, RI, RD, REZ, RKZ, RUZ, RY,RxxTR, R-78xx

2. RS, RSO,3. RL, RN, RF, RA, RC, RX4. RSS, RSD, RQS, RQD, RZ

5. RTD, RTS, RSZ, R-78Axx SMD6. RV, RW, RxxPxx, RxxP2xx7. R5, R6, R7, REC1.5-, REC1.8-, REC3-, REC5-, REC7.5-8. RAA9. RP08, RP1210. RP08-SMD, REC2.2-SMD, REC3-SMD, REC5-SMD, REC7.5-SMD11. REC10, REC15, REC20, REC30, REC40

12. RP10, RP15, RP20, RP30, RP4013. RP40-E

TubesTubes

1. 2.



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7. 8.

10.9.

TubesTubes

3. 4.

6.5.



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TubesTubes

13.

12.

11.



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TapesTapes



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TapesTapes



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NotesNotes

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Date post:	03-Jun-2018
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Application Notes 2006 2nd Edition

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