Datasheet

FUNCTIONALDESCRIPTION
FUELGAUGING
IMPEDANCETRACK™VARIABLES
LoadMode
LoadSelect
bq27510-G1
SLUS927–APRIL2009..................................................................................................................................................................................................... www.ti.com
Thebq27510measuresthecellvoltage,temperature,andcurrenttodeterminebatterySOC.Thebq27510
monitorschargeanddischargeactivitybysensingthevoltageacrossasmall-valueresistor(5mΩto20mΩtyp.)
betweentheSRPandSRNpinsandinserieswiththecell.Byintegratingchargepassingthroughthebattery,
thebattery’sSOCisadjustedduringbatterychargeordischarge.
Thetotalbatterycapacityisfoundbycomparingstatesofchargebeforeandafterapplyingtheloadwiththe
amountofchargepassed.Whenanapplicationloadisapplied,theimpedanceofthecellismeasuredby
comparingtheOCVobtainedfromapredefinedfunctionforpresentSOCwiththemeasuredvoltageunderload.
MeasurementsofOCVandchargeintegrationdeterminechemicalstateofchargeandchemicalcapacity
(Qmax).TheinitialQmaxvaluesaretakenfromacellmanufacturers'datasheetmultipliedbythenumberof
parallelcells.ItisalsousedforthevalueinDesignCapacity.Thebq27510acquiresandupdatesthe
battery-impedanceprofileduringnormalbatteryusage.Itusesthisprofile,alongwithSOCandtheQmaxvalue,
todetermineFullChargeCapacity()andStateOfCharge(),specificallyforthepresentloadandtemperature.
FullChargeCapacity()isreportedascapacityavailablefromafullychargedbatteryunderthepresentloadand
temperatureuntilVoltage()reachestheTermVoltage.NominalAvailableCapacity()andFullAvailableCapacity()
aretheuncompensated(noorlightload)versionsofRemainingCapacity()andFullChargeCapacity()
respectively.
Thebq27510hastwoflagsaccessedbytheFlags()functionthatwarnswhenthebattery’sSOChasfallento
criticallevels.WhenRemainingCapacity()fallsbelowthefirstcapacitythreshold,specifiedinSOC1Set
Threshold,the[SOC1](StateofChargeInitial)flagisset.TheflagisclearedonceRemainingCapacity()rises
aboveSOC1SetThreshold.Thebq27510’sBAT_LOWpinautomaticallyreflectsthestatusofthe[SOC1]flag.
AllunitsareinmAh.
WhenRemainingCapacity()fallsbelowthesecondcapacitythreshold,SOCFSetThreshold,the[SOCF](State
ofChargeFinal)flagisset,servingasafinaldischargewarning.IfSOCFSetThreshold=–1,theflagis
inoperativeduringdischarge.Similarly,whenRemainingCapacity()risesaboveSOCFClearThresholdandthe
[SOCF]flaghasalreadybeenset,the[SOCF]flagiscleared.AllunitsareinmAh.
Thebq27510hasseveraldataflashvariablesthatpermittheusertocustomizetheImpedanceTrack™algorithm
foroptimizedperformance.Thesevariablesaredependentuponthepowercharacteristicsoftheapplicationas
wellasthecellitself.
LoadModeisusedtoselecteithertheconstant-currentorconstant-powermodelfortheImpedanceTrack™
algorithmasusedinLoadSelect(seeLoadSelect).WhenLoadModeis0,theConstantCurrentModelis
used(default).When1,theConstantPowerModelisused.The[LDMD]bitofCONTROL_STATUSreflectsthe
statusofLoadMode.
LoadSelectdefinesthetypeofpowerorcurrentmodeltobeusedtocomputeload-compensatedcapacityinthe
ImpedanceTrack™algorithm.IfLoadMode=0(ConstantCurrent),thentheoptionspresentedinTable8are
available.
Table8.Constant-CurrentModelUsedWhenLoadMode=0
LoadSelectCurrentModelUsed
Value
0Averagedischargecurrentfrompreviouscycle:Thereisaninternalregisterthatrecordstheaveragedischargecurrent
througheachentiredischargecycle.Thepreviousaverageisstoredinthisregister.
1(default)Presentaveragedischargecurrent:Thisistheaveragedischargecurrentfromthebeginningofthisdischargecycle
untilpresenttime.
2Averagecurrent:basedofftheAverageCurrent()
3Current:basedoffofalow-pass-filteredversionofAverageCurrent()(τ=14s)
20SubmitDocumentationFeedbackCopyright©2009,TexasInstrumentsIncorporated
ProductFolderLink(s):bq27510-G1
Not Recommended For New Designs