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POWERSAVEMODEOPERATION
I
skip
66 毫安
Vin
160
I
顶峰
66 毫安
Vin
80
pfm 模式 在 明亮的 加载
比较器 高
比较器 低
比较器 低 2
pwm 模式 在 中等 至 全部 加载
1.6%
0.8%
V
O
tps62200,tps62201
tps62202,tps62203,tps62207
tps62204,tps62205,tps62208
SLVS417D–MARCH2002–REVISEDMAY2004
detaileddescription(持续)
thegmamplifierandinputvoltagedeterminestherisetimeofthesawtoothgenerator;thereforeanychangein
inputvoltageoroutputvoltagedirectlycontrolsthedutycycleoftheconverter.thisgivesaverygoodlineand
loadtransientregulation.
astheloadcurrentdecreases,theconverterentersthepowersavemodeoperation.duringpowersavemode,
theconverteroperateswithreducedswitchingfrequencyinPFMmodeandwithaminimumquiescentcurrentto
maintainhighefficiency.
twoconditionsallowtheconvertertoenterthepowersavemodeoperation.oneiswhentheconverterdetects
thediscontinuousconductionmode.theotheriswhenthepeakswitchcurrentinthep-channelswitchgoes
belowtheskipcurrentlimit.thetypicalskipcurrentlimitcanbecalculatedas
Duringthepowersavemodetheoutputvoltageismonitoredwiththecomparatorbythethresholdscomplow
andcomphigh.astheoutputvoltagefallsbelowthecomplowthresholdsettotypically0.8%abovevout
名义上的,thep-channelswitchturnson.thep-channelswitchisturnedoffasthepeakswitchcurrentisreached.
thetypicalpeakswitchcurrentcanbecalculated:
然后-channelrectifieristurnedonandtheinductorcurrentrampsdown.astheinductorcurrentapproaches
zerothen-channelrectifieristurnedoffandthep-channelswitchisturnedonagain,startingthenextpulse.这
convertercontinuesthesepulsesuntilthecomphighthreshold(settotypically1.6%abovevoutnominal)是
reached.theconverterentersasleepmode,reducingthequiescentcurrenttoaminimum.theconverterwakes
upagainastheoutputvoltagefallsbelowthecomplowthresholdagain.thiscontrolmethodreducesthe
quiescentcurrenttypicallyto15µaandreducestheswitchingfrequencytoaminimum,therebyachievingthe
highconverterefficiency.settingtheskipcurrentthresholdstotypically0.8%and1.6%abovethenominaloutput
voltageatlightloadcurrentresultsinadynamicoutputvoltageachievinglowerabsolutevoltagedropsduring
heavyloadtransientchanges.thisallowstheconvertertooperatewithasmalloutputcapacitorofjust10µf
andstillhavealowabsolutevoltagedropduringheavyloadtransientchanges.refertofigure2fordetailed
operationofthepowersavemode.
figure2.powersavemodethresholdsanddynamicvoltagepositioning
TheconverterentersthefixedfrequencyPWMmodeagainassoonastheoutputvoltagefallsbelowthecomp
low2threshold.
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