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RBIInput
GPIO
LayoutConsiderations
GasGaugeOperation
bq27000,bq27200
SLUS556B–SEPTEMBER2004–REVISEDNOVEMBER2004
functionaldescription(持续)
TheRBIinputpinisusedwithanexternalcapacitortoprovidebackuppotentialtotheinternalregisterswhen
V
CC
dropsbelowV
(por)
.v
CC
isoutputonRBIwhenV
CC
isaboveV
(por)
,chargingthecapacitor.anoptional1
M
Ω
resistorcanbeaddedfromtheRBIpintoV
CC
.thisallowstheictomaintainramregisterdataforan
indefiniteperiodwhenthebatteryvoltageisbelowV
(por)
andabove1.3v.thebqjuniorchecksforram
corruptionbystoringaredundantcopyofthehighbyteofnacandacheckbytecomputedfromlmd,cycl,
cyct,andothercriticaldata.afterareset,thebqjuniorcomparestheredundantnacandcheckbytevalues.
ifthechecksarecorrect,nac,lmd,cycl,andcyctareretained;andthecibitinflagsisleftunchanged.
ifthesechecksarenotcorrect,nac,cycl,andcyctarecleared;lmdisinitializedfromeepromandtheci
bitinflagsissetto1.allotherramisinitializedonallresets.
thegpiopincanbeusedasaninputoranoutput.theinitialstatecanbeestablishedbyprogrammingbit7in
thepkcfgeepromlocation.theinput/outputstatecanbechangedatanytimebychangingthevalueinbit7
ofmode.
theauto-calibratingdsccapproacheffectivelycancelstheinternaloffsetvoltagewithinthebqjunior,butany
externaloffsetcausedbypcblayoutmustbeprogrammedintheeepromtobecancelled.themagnitudeand
variabilityoftheexternaloffsetmakesitcriticaltopayspecialattentiontothepcblayout.toobtainoptimal
效能,thedecouplingcapacitorfromv
CC
toV
SS
andthefiltercapacitorsfromSRPandSRNtoV
SS
shouldbeplacedascloselyaspossibletothebqjunior,withshorttracerunstobothsignalandv
SS
管脚.所有
低-currentv
SS
connectionsshouldbekeptseparatefromthehigh-currentdischargepathfromthebatteryand
shouldtieintothehigh-currenttraceatapointdirectlynexttothesenseresistor.thisshouldbeatrace
connectiontotheedgeorinsideofthesenseresistorconnection,sothatnopartofthev
SS
interconnections
carryanyloadcurrentandnoportionofthehigh-currentpcbtraceisincludedintheeffectivesenseresistor(i.e.
kelvinconnection).
figure4illustratesanoperationaloverviewofthegasgaugefunction.
ThebqJUNIORmeasuresthecapacityofthebatteryduringactualuseconditionsandupdatestheLast
measureddischarge(lmd)registerwiththelatestmeasuredvalue.thebqjuniorretainsthelearnedlmd
valueunlessafullresetoccurs.bymeasuringthecapacitythatthebatterydeliversasitisdischargedfromfullto
theedv1thresholdwithoutanydisqualifyingevents,thebqjuniorlearnsthecapacityofthebattery.这
bqjuniordoesnotneedtolearnanewcapacityoneachfulldischarge,andonlyadischargeduringnormal
useconditionsshouldbeusedtolearnanewcapacity.intheeventthatsomeabnormalsituationoccursthat
couldcauseasignificantreductioninlearnedcapacity,thelmdvalueisrestrictedtoamaximumlmd
学习-downduringanysinglelearningdischargeoflmd/8.thecapacityinaccurate(ci)bitinflagsiscleared
afteralearningcycle.thisbitremainsclearedunlessafullresetoccursorthecyclecountsincethelastlearning
循环(cycl)reachesacountof32.
这
全部
conditionisdefinedasnominalavailablecapacity(nac)=lmd.thevaliddischargeflag(vdq)inthe
FLAGSregisterissetwhenthisconditionoccursandremainssetuntilthelearningdischargecyclecompletesor
aneventoccursthatdisqualifiesthelearningcycle.
ThelearningdischargecyclecompleteswhenthebatteryisdischargedtotheconditionwhereVOLT
≤
EDV1
门槛.theedv1thresholdshouldbesetatavoltagethatensuresatleast6.25%ofbatterycapacitybelow
thatthreshold.theedvfthresholdshouldbesetatavoltagethatthesystemseesasthezero-capacitybattery
电压.thebqjunioredvdetectionisdesignedtopreventprematuredetectionoftheedvthresholdsdueto
dynamicloadvariations.edvdetectionhasadynamicallyadjusteddelayofupto21.5swithrsoc
≥
6%and
downto3swhenrsoc=0%.
thebqjuniordoesnotlearnthecapacitybetweenedv1andedvfthresholds,butassumesthatthecapacity
is6.25%oflmd;所以,careshouldbetakentosetedv1basedonthecharacteristicsofthebattery.这
measuredLMDvalueisdeterminedbymeasuringthecapacitydeliveredfromthebatteryfromNAC=LMDuntil
volt=edv1,pluslmd/16toaccountforthe6.25%capacityremainingbelowtheedv1threshold.
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