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APPLICATIONINFORMATION
BOOSTCONVERTERDESIGNPROCEDURE
D
V
输出
V
D
V
在
V
输出
V
D
V
sw
10 V
0.8 V
3.3 V
10 V
0.8 V
0.5 V
0.73
I
L
I
输出
1
D
300 毫安
1
0.73
1.11 一个
i
L
V
在
V
sw
D
f
s
L
(3.3 V
0.5 v)
0.73
1.6 MHz
4.2
H
304 毫安
I
swpeak
I
L
i
L
2
1.11 一个
304 毫安
2
1.26 一个
InductorSelection
TPS65100
TPS65105
SLVS496B–SEPTEMBER2003–REVISEDMARCH2004
Thefirststepinthedesignprocedureistocalculatethemaximumpossibleoutputcurrentofthemainboost
converterundercertaininputandoutputvoltageconditions.thefollowingexampleisfora3.3-vto10-v
转换:
V
在
=3.3v,v
输出
=10v,switchvoltagedropv
sw
=0.5v,schottkydiodeforwardvoltagev
D
=0.8v
1.dutycycle:
2.averageinductorcurrent:
3.inductorpeak-至-peakripplecurrent:
4.peakswitchcurrent:
.theintegratedswitch,theinductor,andtheexternalschottkydiodemustbeabletohandlethepeakswitch
电流.thecalculatedpeakswitchcurrenthastobeequaltoorlowerthantheminimumn-mosfetswitch
currentlimitasspecifiedintheelectricalcharacteristicstable(1.6aforthetps65100and0.96aforthe
tps65105).ifthepeakswitchcurrentishigher,thentheconvertercannotsupporttherequiredloadcurrent.这个
calculationmustbedonefortheminimuminputvoltagewherethepeakswitchcurrentishighest.thecalculation
includesconductionlosseslikeswitchr
DSon
(0.5v)anddiodeforwarddropvoltagelosses(0.8v).额外的
switchinglosses,inductorcoreandwindinglosses,等,requireaslightlyhigherpeakswitchcurrentintheactual
应用.theabovecalculationstillallowsaforgooddesignandcomponentselection.
severalinductorsworkwiththetps65100/05.especiallywiththeexternalcompensation,theperformancecan
beadjustedtothespecificapplicationrequirements.themainparameterforinductorselectionisthesaturation
currentoftheinductorwhichshouldbehigherthanthepeakswitchcurrentascalculatedabovewithadditional
margintocoverforheavyloadtransientsandextremestart-upconditions.anothermethodistochoosethe
inductorwithasaturationcurrentatleastashighastheminimumswitchcurrentlimitof1.6aforthetps65100
and0.96aforthetps65105.thedifferentswitchcurrentlimitsallowselectionofaphysicallysmallerinductor
whenlessoutputcurrentisrequired.thesecondimportantparameterisinductordcresistance.通常地,这
lowerthedcresistance,thehighertheefficiency.不管怎样,inductordcresistance,isnottheonlyparameter
determiningtheefficiency.especiallyforaboostconverterwheretheinductoristheenergystorageelemen,tthe
typeandmaterialoftheinductorinfluencestheefficiencyaswell.especiallyatthehighswitchingfrequencyof
1.6mhz,inductorcorelosses,proximityeffects,andskineffectsbecomemoreimportant.通常地,aninductor
withalargerformfactoryieldshigherefficiency.theefficiencydifferencebetweendifferentinductorscanvary
between2%to10%.forthetps65100/05,inductorvaluesbetween3.3µhand6.8µhareagoodchoicebut
othervaluescanbeusedaswell.possibleinductorsareshownintable1.
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