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SETTINGTHEOUTPUTVOLTAGE
V
输出
1.233 V
1
R1
R2
(5)
C
FF
1
2
fS
20
R1
(6)
TPS61040
TPS61041
SLVS413B–OCTOBER2002–REVISEDMAY2004
applicationinformation(持续)
Themaximumloadcurrentoftheconveteristhecurrentattheoperationpointwherethecoverterstartstoenter
thecontinuousconductionmode.usuallytheconvertershouldalwaysoperateindiscontinuousconduction
模式.
last,theselectedinductorshouldhaveasaturationcurrentthatmeetsthemaximumpeakcurrentofthe
转换器(ascalculatedinthe
peakcurrentcontrol
部分).usethemaximumvaluefori
LIM
forthiscalculation.
anotherimportantinductorparameteristhedcresistance.thelowerthedcresistance,thehighertheefficiency
oftheconverter.refertothetable1andthetypicalapplicationsfortheinductorselection.
table1.recommendedinductorfortypicallcdbiassupply(seefigure15)
DEVICEINDUCTORVALUECOMPONENTSUPPLIERCOMMENTS
10µhsumidacr32-100highefficiency
10µhsumidacdrh3d16-100highefficiency
TPS6104010µHMurataLQH4C100K04Highefficiency
4.7µhsumidacdrh3d16-4r7smallsolutionsize
4.7µhmuratalqh3c4r7m24smallsolutionsize
Highefficiency
TPS6104110µHMurataLQH3C100K24
Smallsolutionsize
theoutputvoltageiscalculatedas:
ForbatterypoweredapplicationsahighimpedancevoltagedividershouldbeusedwithatypicalvalueforR2of
≤
200k
Ω
andamaximumvalueforr1of2.2m
Ω
.smallervaluesmightbeusedtoreducethenoisesensitivityof
thefeedbackpin.
AfeedforwardcapacitoracrosstheupperfeedbackresistorR1isrequiredtoprovidesufficientoverdriveforthe
errorcomparator.withoutafeedforwardcapacitor,oronewhosevalueistoosmall,thetps61040/41shows
doublepulses
orapulseburstinsteadofsinglepulsesattheswitchnode(sw),causinghigheroutputvoltage
波纹.ifthishigheroutputvoltagerippleisacceptable,thefeedforwardcapacitorcanbeleftout.
thelowertheswitchingfrequencyoftheconverter,thelargerthefeedforwardcapacitorvaluerequired.agood
startingpointistousea10pffeedforwardcapacitor.asafirstestimation,therequiredvalueforthefeedforward
capacitorattheoperationpointcanalsobecalculatedusingthefollowingformula:
在哪里:
R1=Upperresistorofvoltagedivider
fs=switchingfrequencyoftheconverteratthenominalloadcurrent(seeprevioussectionforcalculating
theswitchingfrequency)
C
FF
=Chooseavaluethatcomesclosesttotheresultofthecalculation
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