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OffsetCalibration
DigitalMagnitudeFilter
电压
温度
bq27000,bq27200
SLUS556B–SEPTEMBER2004–REVISEDNOVEMBER2004
functionaldescription(持续)
TheoffsetvoltageoftheDSCCmeasurementmustbeverylowtobeabletomeasuresmallsignallevels
准确地.thebqjuniorprovidesanauto-calibrationfeaturetocanceltheinternalvoltageoffseterroracross
srpandsrnformaximumchargemeasurementaccuracy.
NOCALIBRATIONISREQUIRED
.外部
voltageoffseterrorcausedbythepcblayoutcannotbeautomaticallycalibratedoutbythegauge,butthe
externaloffsetcanbedeterminedusingabuilt-inuseroffsetmeasurementcommandandcanbeprogrammed
intotheeepromforinclusionintheoffsetcompensationperformedbythegauge.seethe
布局
仔细考虑
sectionfordetailsonminimizingpcbinducedoffsetacrossthesrpandsrnpins.
thebqjuniorauto-calibrationofthedsccoffsetisperformedfromtime-至-timeasoperatingconditions
改变,tokeepthemeasurementerrorsmall.acalibration-在-progress(calip)flagissetinflagstoindicate
whentheoperationoccurs.capacity,电压,andtemperatureisupdatedduringthe5.12secondoffset
calibrationtime,butotherparametersarenotupdateduntilthecalibrationhascompleted.whenthereisafull
重置,thegaugemakesaninitialquickoffsetcalibrationanddelaysthe5.12secondfulloffsetcalibrationforat
least40seconds.thisisdonetopreventthefull5.12secondcalibrationoperationfrominterferingwithmodule
testfunctionsthatneedtobeperformedimmediatelyafterpowerapplicationduringmanufacturingtest.这
quickoffsetcalibrationafterafullresetisa1.28secondoffsetmeasurmentusedasadelay,followedbya1.28
secondoffsetmeasurementthatisusedastheinitialoffsetvalue.the1.28seconddelayallowsv
CC
tosettle
beforetheinitialoffsetmeasurement.ifmanufacturingtestdoesnotneedtheadditionalv
CC
settlingtimeorcan
useaslightlyworseinitialoffsetmeasurement,thetestermaywritebit
0
ofctrl(address0x00)至
1
duringthe
first1.28secondsaftertheresetandthefirstoffsetsampleisused,cuttingtheinitialquickoffsetcalibrationtime
inhalf.
thedigitalmagnitudefilter(dmf)thresholdcanbesetineepromtoindicateathresholdbelowwhichany
chargeordischargeaccumulationisignored.thisallowssettingathresholdabovethemaximumdsccoffset
expectedfromtheicandpcbcombination,sothatwhennochargeordischargecurrentispresent,这
measuredcapacitychangebythebqjunioriszero.notethatevenasmalloffsetcanadduptoalargeerror
overalongperiod.inadditiontosettingthethresholdabovethelargestoffsetexpected,thedmfshouldbeset
belowtheminimumsignalleveltobemeasured.thesenseresistorvalueshouldbelargeenoughtoallowthe
minimumcurrentleveltoprovideasignallevelsubstantiallyhigherthanthemaximumoffsetvoltage.相反地,
thesenseresistormustbesmallenoughtomeetthesystemrequirementforinsertionlossaswellaskeepthe
maximumvoltageacrossthesenseresistorbelowthe100mvmaximumthatthedscccanaccuratelymeasure.
thedmfthresholdisprogrammedineeprominincrementsof4.9µv.programmingazerointhedmfvalue
willdisablethedmffunctionandallnon-zerodsccmeasurementsarecounted.
ThebqJUNIORmonitorsthebatteryvoltagethroughtheBATpinandreportsanoffsetcorrectedvaluethrough
theinternalregisters.thebqjunioralsomonitorsthevoltagefortheend-的-释放(edv)门槛.这
edvthresholdlevelsareusedtodeterminewhenthebatteryhasbeendischargedto6.25%or
empty
和
synchronizesthereportedcapacitytotheselevelswhentheprogrammededvthresholdsaredetected.
ThebqJUNIORusesanintegratedtemperaturesensortomonitorthepacktemperatureandisreportedthrough
theinternalregisters.thetemperaturemeasurementisusedtoadjustcompensatedavailablecapacityand
自-dischargecapacityloss.
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