www.德州仪器.com
电源-pathmanagement
交流
USB BAT
输出
bq2403x
PACK+
PACK−
系统
VDC
地
VBUS
地
D+
d −
usb 端口
交流Adapter
+
Q1
Q2Q3
UDG−04082
40
m
Ω
(2)
case1:acmode(psel=高)
bq24030,bq24031,bq24032,
bq24032a,bq24035,bq24038,bq24039
SLUS618C–AUGUST2004–REVISEDJUNE2005
thebqtiny-iiipowersthesystemwhileindependentlychargingthebattery.thisfeaturesreducesthecharge
anddischargecyclesonthebattery,allowsforproperchargetermination,andallowsthesystemtorunwithan
absentordefectivebatterypack.thisfeaturegivesthesystempriorityoninputpower,allowingthesystemto
powerupwithadeeplydischargedbatterypack.thisfeatureworksasfollows(notethatpselisassumedhigh
forthisdiscussion).
figure4.电源-pathmanagement
SystemPower
inthiscase,thesystemloadispowereddirectlyfromtheacadapterthroughtheinternaltransistorq1(看
Figure4).forbq24030/1,q1actsasaswitchaslongastheacinputremainsatorbelow6v(v
o(输出-reg)
).
oncetheacvoltagegoesabove6v,q1startsregulatingtheoutputvoltageat6v.forbq24035/39,oncethe
ACvoltagegoesaboveV
截-止
(~6.4v),q1turnsoff.forbq24032/2a/8,theoutputisregulatedat4.4vfrom
theacinput.notethatswitchq3isturnedoffforbothdevices.ifthesystemloadexceedsthecapacityofthe
供应,theoutputvoltagedropsdowntothebattery'svoltage.
ChargeControl
whenacispresent,thebatteryischargedthroughswitchq2basedonthechargeratesetontheiset1input.
dynamicpower-pathmanagement(dppm)
thisfeaturemonitorstheoutputvoltage(systemvoltage)forinputpowerlossduetobrownouts,currentlimiting,
orremovaloftheinputsupply.ifthevoltageontheoutpindropstoapresetvalue,v
(dppm)
×sf,duetoa
limitedamountofinputcurrent,thenthebatterychargingcurrentisreduceduntiltheoutputvoltagestops
dropping.thedppmcontroltriestoreachasteady-stateconditionwherethesystemgetsitsneededcurrentand
thebatteryischargedwiththeremainingcurrent.noactivecontrollimitsthecurrenttothesystem;因此,如果
thesystemdemandsmorecurrentthantheinputcanprovide,theoutputvoltagedropsjustbelowthebattery
voltageandq2turnsonwhichsupplementstheinputcurrenttothesystem.dppmhasthreemainadvantages.
1.thisfeatureallowsthedesignertoselectalowerpowerwalladapter,iftheaveragesystemloadismoderate
comparedtoitspeakpower.forexample,ifthepeaksystemloadis1.75a,averagesystemloadis0.5a
andbatteryfast-chargecurrentis1.25a,thetotalpeakdemandcouldbe3a.withdppm,a2-aadaptor
couldbeselectedinsteadofa3.25-asupply.duringthesystempeakloadof1.75aandchargeloadof1.25
一个,thesmalleradaptor’svoltagedropsuntiltheoutputvoltagereachesthedppmregulationvoltage
门槛.thechargecurrentisreduceduntilthereisnofurtherdropontheoutputvoltage.thesystemgets
its1.75-achargeandthebatterychargecurrentisreducedfrom1.25ato0.25a.whenthepeaksystem
loaddropsto0.5a,thechargecurrentreturnsto1aandtheoutputvoltagereturnstoitsnormalvalue.
2.usingdppmprovidesapowersavingscomparedtoconfigurationswithoutdppm.withoutdppm,ifthe
systemcurrentpluschargecurrentexceedthesupply’scurrentlimit,thentheoutputispulleddowntothe
电池.linearchargersdissipatetheunusedpower(v
在
-v
输出
)×i
加载
.thecurrentremainshigh(atcurrent
限制)andthevoltagedropislargeformaximumpowerdissipation.withdppm,thevoltagedropisless
(v
在
-v
(dppm-reg)
)tothesystemwhichmeansbetterefficiency.theefficiencyforchargingthebatteryisthe
sameforbothcases.theadvantagesincludelesspowerdissipation,lowersystemtemperature,andbetter
overallefficiency.
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