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5FUNCTIONALDESCRIPTION
5.1FUELGAUGING
bq27500
bq27501
System-SideImpedanceTrack™FuelGauge
SLUS785–SEPTEMBER2007
Table4-7.DataFlashSummary(continued)
SubclassDataMinMaxDefault
ClassSubclassOffsetNameUnits
IDTypeValueValueValue
RaTables91Pack0Ra0-18
RaTables92Pack1Ra0-18
SeeNote
(2)
RaTables93Pack0Rax0-18
RaTables94Pack1Rax0-18
Calibration104Data0CCGainF40.140.47095mΩ
Calibration104Data4CCDeltaF4298261193046280932.6mΩ
Calibration104Data8CCOffsetI2-3276832767–1667mV
Calibration104Data10BoardOffsetI1–1281270mV
Calibration104Data11IntTempOffsetI1–12812700.1°C
Calibration104Data12ExtTempOffsetI1–12812700.1°C
Calibration104Data13PackVOffsetI1–12812700.1°C
Calibration107Current1DeadbandU102553mA
Security112Codes0UsealedKey0H20x00000xffff––
Security112Codes2UsealedKey1H20x00000xffff––
Security112Codes4Full-AccessKey0H20x00000xffff––
Security112Codes6Full-AccessKey1H20x00000xffff––
Thebq27500/1measuresthecellvoltage,temperature,andcurrenttodeterminebatterySOC.The
bq27500/1monitorschargeanddischargeactivitybysensingthevoltageacrossasmall-valueresistor
(5mΩto20mΩtyp.)betweentheSRPandSRNpinsandinserieswiththecell.Byintegratingcharge
passingthroughthebattery,thecell’sSOCisadjustedduringbatterychargeordischarge.
Thetotalbatterycapacityisfoundbycomparingstatesofchargebeforeandafterapplyingtheloadwith
theamountofchargepassed.Whenanapplicationloadisapplied,theimpedanceofthecellismeasured
bycomparingtheOCVobtainedfromapredefinedfunctionforpresentSOCwiththemeasuredvoltage
underload.MeasurementsofOCVandchargeintegrationdeterminechemicalstateofchargeand
ChemicalCapacity(Qmax).TheinitialQmaxvaluesaretakenfromacellmanufacturers'datasheet
multipliedbythenumberofparallelcells.ItisalsousedforthevalueinDesignCapacity.Thebq27500/1
acquiresandupdatesthebattery-impedanceprofileduringnormalbatteryusage.Itusesthisprofile,along
withSOCandtheQmaxvalue,todetermineFullChargeCapacity()andStateOfCharge(),specificallyfor
thepresentloadandtemperature.FullChargeCapacity()isreportedascapacityavailablefromafully
chargedbatteryunderthepresentloadandtemperatureuntilVoltage()reachestheTermVoltage.
NominalAvailableCapacity()andFullAvailableCapacity()aretheuncompensated(noorlightload)
versionsofRemainingCapacity()andFullChargeCapacity()respectively.
Thebq27500/1hastwoflagsaccessedbytheFlags()functionthatwarnswhenthecell’sSOChasfallen
tocriticallevels.WhenRemainingCapacity()fallsbelowthefirstcapacitythreshold,specifiedinSOC1
Set,the[SOC1](“StateofChargeInitial””)flagisset.Theflagiscleared,onceRemainingCapacity()rises
aboveSOC1Set.AllunitsareinmAh.
WhenRemainingCapacity()fallsbelowthesecondcapacitythreshold,SOCFSet,the[SOCF](“Stateof
ChargeFinal”)flagisset,servingasafinaldischargewarning.IfSOCFSet=–1,theflagisinoperative
duringdischarge.
Similarly,whenRemainingCapacity()risesaboveSOCFClearandthe[SOCF]flaghasalreadybeenset,
the[SOCF]flagwillbecleared,providedSOCFSet≠–1.AllunitsareinmAh.
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