www.德州仪器.com
1
2
3
4
5
0.1 1 10 100
− 最大 电源 消耗 − w
P
D
铜 散热器 范围 − cm
2
T
一个
= 55
°
C
非 空气 流动
150 lfm
250 lfm
0
100
120
140
160
180
pcb 铜 范围 − 在
2
− 热的 阻抗 −
θ
JA
R c/w
°
非 空气 流动
80
60
40
20
0.1 1 10
SOT223PowerDissipation
P
D
最大值
(
3.3
2.5
)
V x 1 一个
800 mW
(10)
R
θ
JA
最大值
(125
55)
°
C
800 mW
87.5
°
C
W
0
1
2
3
6
0 25 50 75 100 150125
T
一个
= 25
°
C
T
一个
− 包围的 temperature −
°
C
4
5
4 在
2
pcb 范围
0.5 在
2
pcb 范围
P
D
(w)
tps78601,tps78618
tps78625,tps78628
tps78630,tps78633
SLVS389D–SEPTEMBER2002–REVISEDOCTOBER2004
fromthedatainfigure29andrearrangingdissipate800mw.theoperatingenvironmentused
equation6,themaximumpowerdissipationforatoconstructfigure30consistedofaboardwith1oz.
differentgroundplaneareaandaspecificambientcopperplanes.thepackageissolderedtoa1oz.
temperaturecanbecomputed.copperpadonthetopoftheboard.thepadistied
throughthermalviastothe1oz.groundplane.
figure29.maximumpowerdissipationvscopper
heatsinkareafigure30.sot223thermalresistancevspcb
范围
FromthedatainFigure30andrearranging
equation6,themaximumpowerdissipationfora
TheSOT223packageprovidesaneffectivemeansof
differentgroundplaneareaandaspecificambient
managingpowerdissipationinsurfacemountappli-
temperaturecanbecomputed(seefigure31).
cations.thesot223packagedimensionsarepro-
videdinthe
MechanicalData
sectionattheendof
thedatasheet.theadditionofacopperplane
directlyunderneaththeSOT223packageenhances
thethermalperformanceofthepackage.
toillustrate,thetps78625inasot223package
waschosen.forthisexample,theaverageinput
voltageis3.3v,theoutputvoltageis2.5v,这
averageoutputcurrentis1a,theambienttempera-
ture55
°
c,noairflowispresent,andtheoperating
environmentisthesameasdocumentedbelow.
neglectingthequiescentcurrent,themaximumaver-
agepoweriscalculatedasshowninequation10:
SubstitutingT
J
maxforT
J
intoEquation6gives
equation11:
(11)
fromfigure30,
R
Θ
JA
vsPCBCopperArea
,这
figure31.sot223powerdissipation
groundplaneneedstobe0.55in
2
forthepartto
13
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