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ceinput(chargeenable)
ThermalShutdownandProtection
TImerFaultRecovery
直流-dcconverter
PowerSaveModeOperation
bq25010
bq25011
bq25012
SLUS615–DECEMBER2004
thecedigitalinputisusedtoenableordisablethechargeprocess.alow-levelsignalonthispinenablesthe
chargeandahigh-levelsignaldisablesthechargeandplacesthedeviceintoalow-powermode.ahigh-至-低
transitiononthispinalsoresetsalltimersandtimerfaultconditions.notethatthisappliestobothacandusb
charging.
thebqhybridmonitorsthejunctiontemperature,t
J
,ofthedieandsuspendschargingift
J
exceedsT
(shtdwn)
.
ChargingresumeswhenT
J
fallsbelowT
(shtdwn)
byapproximately15
°
c.
asshowninfigure3,bqhybridprovidesarecoverymethodtodealwithtimerfaultconditions.thefollowing
summarizesthismethod:
Condition1
:chargevoltageaboverechargethreshold(v
(rch)
)andtimeoutfaultoccurs.
recoverymethod:bqhybridwaitsforthebatteryvoltagetofallbelowtherechargethreshold.thiscould
happenasaresultofaloadonthebattery,自-dischargeorbatteryremoval.oncethebatteryfallsbelowthe
rechargethreshold,thebqhybridclearsthefaultandstartsanewchargecycle.apororcetogglealso
clearsthefault.
condition2:
chargevoltagebelowrechargethreshold(v
(rch)
)andtimeoutfaultoccurs.
recoverymethod:underthisscenario,thebqhybridappliesthei
(故障)
电流.thissmallcurrentisusedto
detectabatteryremovalconditionandremainsonaslongasthebatteryvoltagestaysbelowtherecharge
门槛.ifthebatteryvoltagegoesabovetherechargethreshold,thenthebqhybriddisablesthei
(故障)
currentandexecutestherecoverymethoddescribedforcondition1.oncethebatteryfallsbelowtherecharge
门槛,thebqhybridclearsthefaultandstartsanewchargecycle.apororcetogglealsoclearsthe
故障.
thebqhybridprovidesalowquiescent-currentsynchronousdc-dcconverter.theinternallycompensated
converterisdesignedtooperateovertheentirevoltagerangeofasingle-cellli-ionorli-polbattery.下面
nominalloadcurrent,thedeviceoperateswithafixedpwmswitchingfrequencyoftypically1mhz.atlightload
电流,thedeviceentersthepowersavemodeofoperation;theswitchingfrequencyisreducedandthe
quiescentcurrentdrawnbytheconverterfromthebat/outpinistypicallyonly15µa.
duringpwmoperationtheconverterusesauniquefast-responsevoltagemodecontrollerschemewithinput
voltagefeedforwardtoachievegoodlineandloadregulationallowingtheuseofsmallceramicinputandoutput
电容.atthebeginningofeachclockcycleinitiatedbytheclocksignal(s),thep-channnelmosfetswitch
isturnedonandtheinductorcurrentrampsupuntilthecomparatortripsandthecontrollogicturnsofftheswitch.
thecurrentlimitcomparatoralsoturnsofftheswitchincasethecurrentlimitofthep-channelswitchis
超过.afterthedeadtimepreventingcurrentshootthroughthen-channnelmosfetrectifieristurnedon
andtheinductorcurrentrampsdown.thenextcycleisinitiatedbytheclocksignalagainturningoffthe
n-channelrectifierandturningontheonthep-channelswitch.theg
M
amplifieraswellastheinputvoltage
determinestherisetimeofthesaw-toothgeneratorandthereforeanychangeininputvoltageoroutputvoltage
directlycontrolsthedutycycleoftheconvertergivingaverygoodlineandloadtransientregulation.
astheloadcurrentdecreasestheconverterentersthepowersavemodeoperation.duringpowersavemode
theconverteroperateswithreducedswitchingfrequencyinPFMmodeandwithaminimumquiescentcurrentto
maintainhighefficiency.
twoconditionsallowtheconvertertoenterthepowersavemodeoperation.oneisthedetectionof
discontinuousconductionmode.theotheriswhenthepeakswitchcurrentinthep-channelswitchgoesbelow
theskipcurrentlimit.thetypicalskipcurrentlimitcanbecalculatedas:
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