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PowerSaveModeandSynchronization
lowbatterydetectorcircuit—lbi/lbo
低-emiswitch
TPS61030
tps61031,tps61032
SLUS534D–SEPTEMBER2002–REVISEDAPRIL2004
detaileddescription(持续)
thesyncpincanbeusedtoselectdifferentoperationmodes.toenablepowersave,syncmustbesetlow.
powersavemodeisusedtoimproveefficiencyatlightload.inpowersavemodetheconverteronlyoperates
whentheoutputvoltagetripsbelowasetthresholdvoltage.itrampsuptheoutputvoltagewithoneorseveral
pulsesandgoesagainintopowersavemodeoncetheoutputvoltageexceedsthesetthresholdvoltage.这个
powersavemodecanbedisabledbysettingthesynctovbat.
Applyinganexternalclockwithadutycyclebetween30%and70%attheSYNCpinforcestheconverterto
operateattheappliedclockfrequency.theexternalfrequencyhastobeintherangeofabout
±
20%ofthe
nominalinternalfrequency.detailedvaluesareshownintheelectricalcharacteristicsectionofthedatasheet.
thelow-batterydetectorcircuitistypicallyusedtosupervisethebatteryvoltageandtogenerateanerrorflag
whenthebatteryvoltagedropsbelowauser-setthresholdvoltage.thefunctionisactiveonlywhenthedeviceis
使能.whenthedeviceisdisabled,thelbopinishigh-阻抗.theswitchingthresholdis500mvatlbi.
duringnormaloperation,lbostaysathighimpedancewhenthevoltage,appliedatlbi,isabovethethreshold.
itisactivelowwhenthevoltageatlbigoesbelow500mv.
thebatteryvoltage,atwhichthedetectioncircuitswitches,canbeprogrammedwitharesistivedivider
connectedtothelbipin.theresistivedividerscalesdownthebatteryvoltagetoavoltagelevelof500mv,
whichisthencomparedtothelbithresholdvoltage.thelbipinhasabuilt-inhysteresisof10mv.seethe
applicationsectionformoredetailsabouttheprogrammingofthelbithreshold.ifthelow-batterydetection
circuitisnotused,thelbipinshouldbeconnectedtognd(ortovbat)andthelbopincanbeleft
unconnected.donotletthelbipinfloat.
ThedeviceintegratesacircuitthatremovestheringingthattypicallyappearsontheSWnodewhenthe
converterentersdiscontinuouscurrentmode.inthiscase,thecurrentthroughtheinductorrampstozeroandthe
rectifyingPMOSswitchisturnedofftopreventareversecurrentflowingfromtheoutputcapacitorsbacktothe
电池.duetotheremainingenergythatisstoredinparasiticcomponentsofthesemiconductorandthe
inductor,aringingontheswpinisinduced.theintegratedantiringingswitchclampsthisvoltagetovbatand
thereforedampensringing.
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