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6.2.2BatteryWithResistorID(bq27501Only)
bq27500
bq27501
System-SideImpedanceTrack™FuelGauge
SLUS785–SEPTEMBER2007
impedanceismeasuredimmediatelyafterbatterydetection.Thebq27500choosestheprofilewhichis
closesttothemeasuredimpedance,startingwiththePacknRaprofiles.Thatis,ifthemeasured
impedancematchesPack0Ra,thenthePack0Raprofileisused.Ifthemeasuredimpedancematches
Pack1Ra,thenthePack1Raprofileisused.Ifthemeasuredimpedancedoesnotmatchtheimpedance
storedineitherPack0RaorPack1Ra,thebatterypackisdeemednew(notanyofthepreviouslyused
packs).EithertheDef0RaorDef1RaprofileiscopiedintoeitherthePack0RaorPack1Raprofile,
dependingonwhichdefaultimpedanceprofilemostcloselymatches.Careistakennottoover-writethe
lastusedPacknRaprofile.
Thebq27501canadministratetheinformationofuptotwobatterypacks.Foragivenpackconnectedto
thefuelgauge,theidentityofthebatteryisdeterminedbyacombinationof(1)readingthepackID
resistorand(2)measuringtheimpedanceofthecurrentlyconnectedpack,and(3)rememberingwhich
packcharacteristicsweremostrecentlyusedbythegauge.
Abatterypack’sIDresistorshouldconnecttotheRIDpinofthefuelgauge.Either'A'Ωor'B'Ωresistor
valuesshouldbeused,toindicatethebatterytype.Ifabatteryconnectionisdetected,bq27501measures
thevoltagedevelopedatRID.IfthevoltageisPack0Voltage,thenitisidentifiedasbatterypackwith'A'
resistorandbq27501willusethePack0Raprofile.IfthevoltagemeasuredisPack1Voltagethenitis
identifiedasbatterypackwith'B'resistorandthebq27501willusePack1Raprofile.Themeasurement
windowaroundeachthresholdisspecifiedbyPackV%Range,whichindicatesthepositiveornegative
deviationaroundeachlevel.ChoosingRIDvaluesof500Ωand8kΩfor'A'and'B',correspondtoPack0
VoltageandPack1Voltagethresholdlevelsof110mVand1070mV,respectively.Theseresistance
valuesassumea300ΩresistancealreadyexistsinfrontoftheRIDpinforESDprotection.
Ifthebq27501measuresavoltageotherthanPack0VoltageorPack1Voltage,thenitsetsthe
ApplicationConfiguration[UNSUPBAT]to‘1’,alertingthesystemthattheinsertedbatteryisnot
supported.Thesystemcanusethisinformationtodownloadthedefaultprofileforthisbatteryifone
exists.Thesystemshouldunsealthegauge,thendownloadthenewbatteryprofileintotheolderDefnRa
memoryprofile.Thelast-usedprofileisindicatedbytheApplicationConfiguration[LU_PROF]bit.
Overwritingtheolderdefaultprofileallowsthebq27501toretaininformationstoredregardingthemost
recentlyusedbattery.Afterthenewdefaultprofileisdownloaded,thebq27501clearstheApplication
Configuration[UNSUPBAT].
Whenthebq27501startsoperationforthefirsttime,itcopiestheDef0RaprofileintothePack0Raprofile
andtheDef1RaprofileintothePack1Raprofile.Thenwhenabatterypackisinsertedforthefirsttime,
thebq27501startsgaugingusingPack0RaprofileifthevoltagemeasuredontheRIDpinisPack0
Voltage,orstartsgaugingusingPack1RaprofileifthevoltagemeasuredontheRIDpinisPack1
Voltage.TheImpedanceTrack™algorithmregularlyupdatesthespecificPacknRaprofileasthebattery
isused.
IfapackisreplacedwithasecondpackhavingthesameresistorIDasthefirst,cellimpedanceis
measuredafterpackdetection,asexplainedinSection6.1.2.1FirstOCVandImpedanceMeasurement.
ThisimpedanceiscomparedwiththeassociatedPacknRaandDefnRaprofilesthatcorrespondtothe
currentRID.IftheimpedancematchesthePacknRaimpedancethenthePacknRaprofileisused.Ifnot,
thebq27501resetsthePacknRadata,bycopyingtheDefnRaprofileintothePacknRaprofile(this
operationoverwritesthepreviouslystoredinformation).TheImpedanceTrack™algorithmbegins
convergingonthedataforthenewbatteryandstoringitinthePacknRaprofile.
32APPLICATION-SPECIFICINFORMATIONSubmitDocumentationFeedback