HR700 datasheet(4/7 Pages) INTERPOINT

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tHermaL management

calculating maXimum ambient temperature

The HR700 Series of DC/DC converters has an upper operating

temperatureof+85°Catthebaseplateofthecase.Thedegreeof

heat sinkingrequired toremain withinthislimitmaybedetermined

fromFigure1whichshowsthemaximumallowedinternalpowerdissi-

pation(PDISSvs.ambienttemperatureforvariousheatsinkthermal

resistances.PDISSmaybecalculatedas:

PDISS=POUT/efficiency–POUT

TheefficiencyforallcombinationsofPOUTandVINforthevarious

modelsmaybeobtainedfromthegraphsontheprecedingpages.

Example:Converter=HR702-2815,TAmB=70°C,

VIN=28VDC,POUT=45watts

Efficiency=85%(FromFigure7)

PDISS=(45/85)–45=7.95watts

FromFigure1wecanseethatthissituationwillrequirethermalresis-

tanceofapproximately4.5°C/watt.

Conversely we may also find the maximum ambient temperature

whichcanbetoleratedifweknowtheheatsinkthermalresistance.

Example:Converter=HR701-2805,VIN=28VDC,POUT=45W.

ThermalResistance=3°C/watt.

Efficiency=83.5%(FromFigure3)

PDISS=(45/0.835)–45=8.89watts.

FromFigure1wecanseethatthemaximumallowedambienttemper-

atureisapproximately75°C.

heat sink recommenDations

AnmFWSeriesconverterinstillair(otherthanconvectivecurrents)

and with no conductive cooling paths other than through electrical

connectionsatthepinswillexhibitathermalresistanceofapproxi-

mately4°C/watt.Incaseswherethisvalueprovestobetoohighitis

recommendedthatadditionalheatsinkingbesupplied.Thesimplest

methodofaccomplishingthisistofirmlyattachtheconvertertoaPCB

thereby providing a conductive thermal path. Secondly it is recom-

mendedthatairflowbeprovidedovertheconverter.Althougheach

situation requires a thorough thermal analysis these two measures

canreducethethermalresistancetoaslowas2°C/watt.Ifcalcula-

tionsindicatefurtherheatsinkingisrequireditisrecommendedthat

additionalthermalmassbeprovidedeitherunderthebaseplateoron

topoftheconverter’smountingflangesorboth.

Degrees Centigrade

° 40° 60° 80° 100° 120° 140°

U=4

°C/

3°C/

2°C/

U=0

°C/

Internal Power Dissipation (max)

vs. Ambient Temperature

FIGuRE 1

pin Out

FIGuRE 2: PIN OuT

SeecaseLfordimensions.

pin dual Output

triple Output

1 PositiveInput

PositiveInput

2 CaseGround

CaseGround

3 InputCommon

InputCommon

4 Inhibit/SyncIn

Inhibit/SyncIn

5 NegativeOutput

Neg.Aux.Output

6 PositiveOutput

PositiveAux.Output

7,8 OutputCommon

OutputCommon

9,10NoConnection

main(+5)Output

Squared corner indicates pin one.

BOTTOM VIEW

MFW

HR700

SERIES

70WATT

Dc/Dc conVerters

Page4of7

HR700RevC-20100212

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