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5.8.2WAKE-UPCOMPARATOR
5.8.3FLASHUPDATES
5.9AUTOCALIBRATION
bq27500
bq27501
System-SideImpedanceTrack™FuelGauge
SLUS785–SEPTEMBER2007
Thewakeupcomparatorisusedtoindicateachangeincellcurrentwhilethebq27500/1isineither
SLEEPorHIBERNATEmodes.OperationConfigurationusesbits[RSNS1-RSNS0]tosetthesense
resistorselection.OperationConfigurationalsousesthe[IWAKE]bittoselectoneoftwopossible
voltagethresholdrangesforthegivensenseresistorselection.Aninternalinterruptisgeneratedwhenthe
thresholdisbreachedineitherchargeordischargedirections.Settingboth[RSNS1]and[RSNS0]to"0"
disablesthisfeature.
Table5-4.I
WAKE
ThresholdSettings
(1)
RSNS1RSNS0IWAKEVth(SRP-SRN)
000Disabled
001Disabled
0101.25mVor–1.25mV
0112.5mVor–2.5mV
1002.5mVor–2.5mV
1015mVor–5mV
1105mVor–5mV
11110mVor–10mV
(1)Theactualresistancevaluevs.thesettingofthesenseresistorisnotimportantjusttheactualvoltage
thresholdwhencalculatingtheconfiguration.
DataFlashcanonlybeupdatedifVoltage()≥FlashUpdateOKVoltage.Flashprogrammingcurrentcan
causeanincreaseinLDOdropout.ThevalueofFlashUpdateOKVoltageshouldbeselectedsuchthat
thebq27500/1V
CC
voltagedoesnotfallbelowitsminimumof2.4VduringFlashwriteoperations.
Thebq27500providesanautocalibrationfeaturethatmeasuresthevoltageoffseterroracrossSRPand
SRNasoperatingconditionschange.Itsubtractstheresultingoffseterrorfromnormalsenseresistor
voltage,V
SR
,formaximummeasurementaccuracy.
AutocalibrationoftheADCbeginsonentrytoSLEEPmode,exceptifTemperature()is<=5°Cor
Temperature()>=45°C.
Thefuelgaugealsoperformsasingleoffsetwhen(1)theconditionofAverageCurrent()≤100mAand(2)
{voltagechangesincelastoffsetcalibration≥256mV}or{temperaturechangesincelastoffsetcalibration
isgreaterthan80°Cfor≥60s}.
Capacityandcurrentmeasurementswillcontinueatthelastmeasuredrateduringtheoffsetcalibration
whenthesemeasurementscannotbeperformed.Ifthebatteryvoltagedropsmorethan32mVduringthe
offsetcalibration,theloadcurrenthaslikelyincreasedconsiderably;hence,theoffsetcalibrationwillbe
aborted.
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