ꢀ
ꢀ
((1/η )ꢀ-ꢀ1)ꢀ×ꢀoutputꢀpowerꢀ=ꢀpowerꢀlosses.ꢀ
ꢀηꢀ=ꢀefficiencyꢀofꢀregulator.ꢀExample:ꢀ95%ꢀ=ꢀ0.95
B.ꢀ
gramꢀ
malꢀ
FindꢀtheꢀvalueꢀofꢀtheꢀthermalꢀresistanceꢀRthꢀTref-Aꢀinꢀtheꢀdia-
byꢀusingꢀtheꢀairflowꢀspeedꢀatꢀtheꢀmodule.ꢀTakeꢀtheꢀther-
resistanceꢀ×ꢀpowerlossꢀtoꢀgetꢀtheꢀtemperatureꢀincrease.
A.ꢀTheꢀpowerlossꢀisꢀcalculatedꢀbyꢀusingꢀtheꢀformula
Thermal Considerations
General
Calculation of ambient temperature
TheꢀPMBꢀ4000ꢀSeriesꢀDC/DCꢀregulatorsꢀareꢀdesignedꢀ
toꢀoperateꢀinꢀaꢀvarietyꢀofꢀthermalꢀenvironments,ꢀhoweverꢀ
sufficientꢀcoolingꢀshouldꢀbeꢀprovidedꢀtoꢀhelpꢀensureꢀreliableꢀ
operation.ꢀHeatꢀisꢀremovedꢀbyꢀconduction,ꢀconvectionꢀandꢀ
radiationꢀtoꢀtheꢀsurroundingꢀenvironment.ꢀIncreasedꢀairflowꢀ
enhancesꢀtheꢀheatꢀtransferꢀviaꢀconvection.ꢀꢀ
Byꢀusingꢀtheꢀthermalꢀresistanceꢀtheꢀmaximumꢀallowedꢀꢀ
ambientꢀtemperatureꢀcanꢀbeꢀcalculated.ꢀ
Properꢀcoolingꢀcanꢀbeꢀverifiedꢀbyꢀmeasuringꢀtheꢀ
temperatureꢀatꢀtheꢀreferenceꢀpointꢀ(T ).
ref
<«$ꢈ8>
ꢁNBYꢂꢀꢀꢃꢂ«$ꢄ
5
SFG
ꢃꢂ
ꢂꢊ7JOꢁꢊꢅꢉꢅꢊ7PVUꢁꢊꢊꢅꢉꢅꢊ7JOꢊꢃꢉꢀꢌꢃꢉꢋꢊ7PVU
ꢅꢉꢅꢊ7JOꢁꢊꢄꢉꢂꢊ7PVU
ꢃꢄ
ꢀ
ꢂꢊ7JOꢁꢊꢃꢉꢄꢁꢊꢄꢉꢂꢊ7PVU
ꢂꢊ7JOꢁꢊꢃꢉꢀꢁꢊꢃꢉꢂꢁꢊꢃꢉꢋꢊ7PVU
ꢇ
ꢆ
ꢅ
ꢀ
TheꢀPMBꢀ4000ꢀthermalꢀtestingꢀisꢀperformedꢀwithꢀtheꢀ
productꢀmountedꢀonꢀanꢀFR4ꢀboardꢀ254ꢀ×ꢀ254ꢀmmꢀwithꢀ8ꢀ
ꢀꢁꢀ
ꢀꢁꢂ
ꢃꢁꢀ
ꢃꢁꢂ
ꢄꢁꢀ
ꢄꢁꢂ
ꢅꢁꢀ <NꢈT>
layersꢀofꢀ35ꢀµmꢀcopper.ꢀAirflowꢀisꢀperpendicularꢀtoꢀtheꢀT ꢀ
ref
side.
Thermalꢀresistanceꢀvs.ꢀairspeedꢀmeasuredꢀatꢀtheꢀregulator.ꢀꢀ
C.ꢀMaxꢀallowedꢀcalculatedꢀambientꢀtemperatureꢀis:ꢀ
ꢀꢀꢀꢀMaxꢀT ꢀofꢀDC/DCꢀregulatorꢀ-ꢀtemperatureꢀincrease.
ref
choke
Example:ꢀꢀ5Vꢀinput,ꢀ1.8ꢀVꢀoutputꢀatꢀ1m/s,ꢀfullꢀload:ꢀ
A.ꢀ((1/0.9)ꢀ-ꢀ1)ꢀ×ꢀ28.8ꢀWꢀ=ꢀ3.2ꢀWꢀ
airflow
B.ꢀ3.2ꢀWꢀ×ꢀ9ꢀ°C/Wꢀ=ꢀ28.8ꢀ°Cꢀ
C.ꢀ90ꢀ°Cꢀ-ꢀ28.8ꢀ°Cꢀ=ꢀmaxꢀambientꢀtemperatureꢀisꢀ61.2ꢀ°Cꢀꢀ
Test board
Theꢀrealꢀtemperatureꢀwillꢀbeꢀdependentꢀonꢀseveralꢀfactors,ꢀ
likeꢀPCBꢀsizeꢀandꢀtype,ꢀdirectionꢀofꢀairflow,ꢀairꢀturbulenceꢀ
etc.ꢀItꢀisꢀrecommendedꢀtoꢀverifyꢀtheꢀtemperatureꢀbyꢀtesting.ꢀ
ꢀꢅ
ꢀꢀꢀꢀꢀꢀEN/LZTꢀ146ꢀ049ꢀR4Aꢀ©EricssonꢀPowerꢀModules,ꢀMarchꢀ2007
PMBꢀ4518TꢀWPꢀDatasheet
ERICSSON [ ERICSSON ]
