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5.2IMPEDANCETRACK™VARIABLES
bq27500
bq27501
System-SideImpedanceTrack™FuelGauge
SLUS785–SEPTEMBER2007
Thebq27500/1hasseveraldataflashvariablesthatpermittheusertocustomizetheImpedanceTrack™
algorithmforoptimizedperformance.Thesevariablesaredependentuponthepowercharacteristicsofthe
applicationaswellasthecellitself.
LoadMode
LoadModeisusedtoselecteithertheconstantcurrentorconstantpowermodelfortheImpedanceTrack™algorithmasusedin
LoadSelect(seeLoadSelect).WhenLoadModeis0,theConstantCurrentModelisused(default).When1,theConstant
PowerModelisused.The[LDMD]bitofCONTROLSTATUSreflectsthestatusofLoadMode.
LoadSelect
LoadSelectdefinesthetypeofpowerorcurrentmodeltobeusedtocomputeload-compensatedcapacityintheImpedance
Track™algorithm.IfLoadMode=0(ConstantCurrent)thentheoptionspresentedinTable5-1areavailable.
Table5-1.Constant-CurrentModelUsedWhenLoadMode=0
LoadSelectValueCurrentModelUsed
Averagedischargecurrentfrompreviouscycle:Thereisaninternalregisterthatrecordstheaveragedischarge
0
currentthrougheachentiredischargecycle.Thepreviousaverageisstoredinthisregister.
Presentaveragedischargecurrent:Thisistheaveragedischargecurrentfromthebeginningofthisdischarge
1(default)
cycleuntilpresenttime.
2AverageCurrent:basedonAverageCurrent()
3Current:basedoffofalow-pass-filteredversionofAverageCurrent()(τ=14s)
4DesignCapacity/5:CRatebasedoffofDesignCapacity/5oraC/5rateinmA.
5AtRate(mA):UsewhatevercurrentisinAtRate()
6User_Rate-mA:UsethevalueinUser_Rate().Thisgivesacompletelyuserconfigurablemethod.
IfILoadMode=1(ConstantPower)thenthefollowingoptionsshowninTable5-2areavailable.
Table5-2.Constant-PowerModelUsedWhenLoadMode=1
LoadSelectValuePowerModelUsed
Averagedischargepowerfrompreviouscycle:Thereisaninternalregisterthatrecordstheaveragedischarge
0
powerthrougheachentiredischargecycle.Thepreviousaverageisstoredinthisregister.
Presentaveragedischargepower:Thisistheaveragedischargepowerfromthebeginningofthisdischargecycle
1(default)
untilpresenttime.
2AverageCurrent×Voltage:basedofftheAverageCurrent()andVoltage().
3Current×Voltage:basedoffofalow-pass-filteredversionofAverageCurrent()(τ=14s)andVoltage()
4DesignEnergy/5:CRatebasedoffofDesignEnergy/5oraC/5rateinmA.
5AtRate(10mW):UsewhatevervalueisinAtRate().
6User_Rate-10mW:UsethevalueinUser_Rate()mW.Thisgivesacompletelyuserconfigurablemethod.
ReserveCap-mAh
ReserveCap-mAhdetermineshowmuchactualremainingcapacityexistsafterreaching0RemainingCapacity(),before
TerminateVoltageisreached.Ano-loadrateofcompensationisappliedtothisreserve.
ReserveCap-mWh
ReserveCap-mWhdetermineshowmuchactualremainingcapacityexistsafterreaching0AvailableEnergy(),before
TerminateVoltageisreached.Ano-loadrateofcompensationisappliedtothisreservecapacity.
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