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THERMALINFORMATION
T
J
一个
R
θ
JC
T
C
B
R
θ
CS
T
一个
C
R
θ
SA
(一个)
sot223 包装
电路 板 铜 范围
B
一个
C
T
J
T
一个
P
D
最大值
R
θ
JC
R
θ
CS
R
θ
SA
(5)
P
D
最大值
V
在(avg)
V
输出(avg)
I
输出(avg)
V
i(avg)
I
(q)
tps79501,tps79516
tps79518,tps79525
tps79530,tps79533
SLVS350B–OCTOBER2002–REVISEDOCTOBER2004
TheamountofheatthatanLDOlinearregulator
generatesisdirectlyproportionaltotheamountof
poweritdissipatesduringoperation.allintegrated
circuitshaveamaximumallowablejunctiontempera-
ture(t
j(最大值)
)abovewhichnormaloperationisnot
使确信.asystemdesignermustdesignthe
operatingenvironmentsothattheoperatingjunction
温度(t
J
)doesnotexceedthemaximum
junctiontemperature(t
j(最大值)
).thetwomainenviron-
mentalvariablesthatadesignercanusetoimprove
thermalperformanceareairflowandexternal
heatsinks.thepurposeofthisinformationistoaid
thedesignerindeterminingtheproperoperating
environmentforalinearregulatorthatisoperatingat
aspecificpowerlevel.
figure25.thermalresistances
ingeneral,themaximumexpectedpower(p
d(最大值)
)
consumedbyalinearregulatoriscomputedas
equation5summarizesthecomputation:
equation4:
TheR
Θ
JC
isspecifictoeachregulatorasdetermined
(4)
byitspackage,引线框架,anddiesizeprovidedin
在哪里:
theregulator'sdatasheet.ther
Θ
SA
isafunctionof
thetypeandsizeofheatsink.forexample,
黑色
•
V
在(avg)
istheaverageinputvoltage
bodyradiator
typeheatsinkscanhaveR
Θ
CS
值
•
V
输出(avg)
istheaverageoutputvoltage
rangingfrom5
°
c/wforverylargeheatsinksto
•
I
输出(avg)
istheaverageoutputcurrent
50
°
c/wforverysmallheatsinks.ther
Θ
CS
isa
•
I
(q)
isthequiescentcurrent
functionofhowthepackageisattachedtothe
散热器.forexample,ifathermalcompoundisused
formosttildoregulators,thequiescentcurrentis
toattachaheatsinktoasot223package,r
Θ
CS
的
insignificantcomparedtotheaverageoutputcurrent;
1
°
c/wisreasonable.
因此,thetermv
在(avg)
xI
(q)
canbeneglected.
Theoperatingjunctiontemperatureiscomputedby
Evenifnoexternal
blackbodyradiator
typeheatsink
addingtheambienttemperature(t
一个
)andthein-
isattachedtothepackage,theboardonwhichthe
creaseintemperatureduetotheregulator'spower
regulatorismountedprovidessomeheatsinking
消耗.thetemperatureriseiscomputedby
throughthepinsolderconnections.somepackages,
multiplyingthemaximumexpectedpowerdissipation
liketheddpakandsot223packages,useacopper
bythesumofthethermalresistancesbetweenthe
planeunderneaththepackageorthecircuitboard's
junctionandthecase(r
Θ
JC
),thecasetoheatsink
groundplaneforadditionalheatsinkingtoimprove
(r
Θ
CS
),andtheheatsinktoambient(r
Θ
SA
).热的
theirthermalperformance.computeraidedthermal
resistancesaremeasuresofhoweffectivelyanobject
modelingcanbeusedtocomputeveryaccurate
dissipatesheat.典型地,thelargerthedevice,这
approximationsofanintegratedcircuit'sthermalper-
moresurfaceareaavailableforpowerdissipationand
formanceindifferentoperatingenvironments(e.g.,
thelowertheobject'sthermalresistance.
differenttypesofcircuitboards,differenttypesand
sizesofheatsinks,anddifferentairflows,等.).使用
figure25illustratesthesethermalresistancesfor(一个)
thesemodels,thethreethermalresistancescanbe
asot223packagemountedinajedeclow-k
combinedintoonethermalresistancebetweenjunc-
板.
tionandambient(r
Θ
JA
).thisr
Θ
JA
isvalidonlyforthe
specificoperatingenvironmentusedinthecomputer
模型.
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