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DETAILEDDESCRIPTION
运作
constantfrequencymodeoperation(同步=高)
powersavemodeoperation(同步=低)
TPS62110
TPS62111
TPS62112
SLVS585–JULY2005
thetps6211xisasynchronousstep-downconverterthatoperateswitha1-mhzfixedfrequencypulsewidth
调制(pwm)atmoderate-至-heavyloadcurrentsandentersthepowersavemodeatlightloadcurrent.
duringpwmoperation,theconverterusesauniquefastresponsevoltagemodecontrolschemewithinput
voltagefeedforward.goodlineandloadregulationisachievedwiththeuseofsmallinputandoutputceramic
电容.atthebeginningofeachclockcycleinitiatedbytheclocksignal(s),thep-channelmosfetswitch
isturnedon,andtheinductorcurrentrampsupuntilthecomparatortripsandthecontrollogicturnstheswitch
止.theswitchisturnedoffbythecurrentlimitcomparatorifthecurrentlimitofthep-channelswitchis
超过.afterthedeadtimepreventscurrentshootthrough,然后-channelmosfetrectifieristurnedon,和
theinductorcurrentrampsdown.thenextcycleisinitiatedbytheclocksignalturningoffthen-channelrectifier,
andturningonthep-channelswitch.
theerroramplifieraswellastheinputvoltagedeterminestherisetimeofthesawtoothgenerator.因此,
anychangeininputvoltageoroutputvoltagedirectlycontrolsthedutycycleoftheconvertergivingaverygood
lineandloadtransientregulation.
inconstantfrequencymode,theoutputvoltageisregulatedbyvaryingthedutycycleofthepwmsignalinthe
rangeof100%to10%.connectingthesyncpintoavoltagegreaterthan1.5vforcestheconvertertooperate
permanentlyinthepwmmodeevenatlightorno-loadcurrents.theadvantageisthattheconverteroperates
withafixedswitchingfrequencythatallowssimplefilteringoftheswitchingfrequencyfornoise-敏感的
产品.inthismode,theefficiencyislowercomparedtothepowersavemodeduringlightloads.这
n-mosfetofthedevicesstayonevenwhenthecurrentintotheoutputdropstozero.thispreventsthedevice
fromgoingintodiscontinuousmode,andthedevicetransfersunusedenergybacktotheinput.因此,那里
isnoringingattheoutput,whichusuallyoccursindiscontinuousmode.thedutycyclerangeinconstant
frequencymodeis100%to10%.
ItispossibletoswitchfromforcedPWMmodetothepowersavemodeduringoperationbypullingtheSYNCpin
低.theflexibleconfigurationofthesyncpinduringoperationofthedeviceallowsefficientpower
managementbyadjustingtheoperationofthetps6211xtothespecificsystemrequirements.
astheloadcurrentdecreases,theconverterentersthepowersavemodeoperation.duringpowersavemode,
theconverteroperateswithreducedswitchingfrequencyinpulsefrequencymodulation(pfm),andwitha
minimumquiescentcurrenttomaintainhighefficiency.whenevertheaverageoutputcurrentgoesbelowtheskip
门槛,theconverterentersthepowersavemode.theaveragecurrentdependsontheinputvoltage.itis
about200maatlowinputvoltagesandupto400mawithmaximuminputvoltage.theaverageoutputcurrent
mustbebelowthethresholdforatleast32clockcyclestoenterthepowersavemode.duringthepowersave
模式,theoutputvoltageismonitoredwithacomparatorandtheoutputvoltageisregulatedintoatypicalvalue
betweenthenominaloutputvoltageand0.8%abovethenominaloutputvoltage.whentheoutputvoltagefalls
belowthenominaloutputvoltage,thep-channelswitchturnson.thep-channelswitchisturnedoffasthepeak
switchcurrentisreached.然后-channelrectifieristurnedon,andtheinductorcurrentrampsdown.asthe
inductorcurrentapproacheszero,然后-channelrectifieristurnedoffandtheswitchisturnedonstartingthe
nextpulse.whentheoutputvoltagecannotbereachedwithasinglepulse,thedevicecontinuestoswitchwith
itsnormaloperatingfrequencyuntilthecomparatordetectstheoutputvoltagetobe0.8%abovethenominal
outputvoltage.thiscontrolmethodreducesthequiescentcurrentto20µa(典型),andreducestheswitching
frequencytoaminimumthatachievesthehighestconverterefficiency.
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