www.德州仪器.com
R
θ
JA
最大值
(125
55)
°
C
2.5 W
28
°
C
W
(9)
T
J
T
一个
P
D
最大值 x R
θ
JA
(6)
R
θ
JA
T
J
–T
一个
P
D
最大值
(7)
DDPAKPowerDissipation
15
20
25
30
35
40
0.1 1 10 100
铜 散热器 范围 − cm
2
− 热的 阻抗 −
θ
JA
R c/w
°
非 空气 流动
150 lfm
250 lfm
1 oz. 铜
电源 平面
1 oz. 铜
地面 平面
2 oz. 铜 焊盘 垫子
和 25 热的 vias
热的 vias, 0.3 mm
直径, 1,5 mm 程度
P
D
最大值
(
5
2.5
)
V x 1 一个
2.5 W
(8)
tps78601,tps78618
tps78625,tps78628
tps78630,tps78633
SLVS389D–SEPTEMBER2002–REVISEDOCTOBER2004
Evenifnoexternal
blackbodyradiator
typeheatsink
isattachedtothepackage,theboardonwhichthe
regulatorismountedprovidessomeheatsinking
fromfigure27,
DDPAKThermalResistancevs
throughthepinsolderconnections.somepackages,
CopperHeatsinkArea
,thegroundplaneneedstobe
liketheddpakandsot223packages,useacopper
1cm
2
fortheparttodissipate2.5w.theoperating
planeunderneaththepackageorthecircuitboard's
environmentusedinthecomputermodeltoconstruct
groundplaneforadditionalheatsinkingtoimprove
figure27consistedofastandardjedechigh-k
theirthermalperformance.计算机-aidedthermal
板(2s2p)witha1oz.internalcopperplaneand
modelingcanbeusedtocomputeveryaccurate
groundplane.thepackageissolderedtoa2oz.
approximationsofanintegratedcircuit'sthermalper-
copperpad.thepadistiedthroughthermalviasto
formanceindifferentoperatingenvironments(e.g.,
the1oz.groundplane.figure28showstheside
differenttypesofcircuitboards,differenttypesand
viewoftheoperatingenvironmentusedinthecom-
sizesofheatsinks,anddifferentairflows,等.).使用
putermodel.
thesemodels,thethreethermalresistancescanbe
combinedintoonethermalresistancebetweenjunc-
tionandambient(r
Θ
JA
).thisr
Θ
JA
isvalidonlyforthe
specificoperatingenvironmentusedinthecomputer
模型.
equation5simplifiesintoequation6:
rearrangingequation6givesequation7:
UsingEquation6andthecomputermodelgenerated
curvesshowninfigure27andfigure30,adesigner
canquicklycomputetherequiredheatsinkthermal
阻抗/boardareaforagivenambienttempera-
ture,powerdissipation,andoperatingenvironment.
TheDDPAKpackageprovidesaneffectivemeansof
figure27.ddpakthermalresistancevscopper
HeatsinkArea
managingpowerdissipationinsurfacemountappli-
cations.theddpakpackagedimensionsarepro-
videdinthe
MechanicalData
sectionattheendof
thedatasheet.theadditionofacopperplane
directlyunderneaththeDDPAKpackageenhances
thethermalperformanceofthepackage.
toillustrate,thetps78625inaddpakpackage
waschosen.forthisexample,theaverageinput
voltageis5v,theoutputvoltageis2.5v,这
averageoutputcurrentis1a,theambienttempera-
ture55
°
c,theairflowis150lfm,andtheoperating
environmentisthesameasdocumentedbelow.
neglectingthequiescentcurrent,themaximumaver-
agepowerisshowninequation8:
figure28.ddpakthermalresistance
SubstitutingT
J
maxforT
J
intoEquation6gives
equation9:
12
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