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LTC4011 Datasheet(PDF) 21 Page - Linear Technology

Part # LTC4011
Description  High Efficiency Standalone Nickel Battery Charger
PDF  26 Pages
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Manufacturer  LINER [Linear Technology]
Direct Link  http://www.linear.com
Logo LINER - Linear Technology

LTC4011 Datasheet(HTML) 21 Page - Linear Technology

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LTC4011

4011fb
applicaTions inForMaTion
Unlikealloftheotherapplicationsdiscussedsofar,the
batterycontinuestopowerthesystemduringcharging.
TheMCUcouldbepowereddirectlyfromthebatteryor
fromanytypeofpostregulatoroperatingfromthebattery.
Inthisconfiguration,theLTC4011reliesexpresslyonthe
abilityofthehostMCUtoknowwhenloadtransientswill
beencountered.TheMCUshouldthenpausecharging
(andthus–∆Vprocessing)duringthoseeventstoavoid
prematurefastchargetermination.IftheMPUcannotreli-
ablyperformthisfunction,fullPowerPathcontrolshould
beimplemented.Inmostapplications,thereshouldnotbe
anexternalloadonthebatteryduringcharge.Excessive
batteryloadcurrentvariations,suchasthosegenerated
byapost-regulatingPWM,cangeneratesufficientvoltage
noisetocausetheLTC4011toprematurelyterminatea
chargecycleand/orprematurelyrestartafastcharge.In
thiscase,itmaybenecessarytoinhibittheLTC4011after
chargingiscompleteuntilexternalgasgaugecircuitry
indicatesthatrechargingisnecessary.Shutdownpower
isappliedtotheLTC4011throughthebodydiodeofQ2
inthisapplication.
Waveforms
Samplewaveformsforastandaloneapplicationduring
atypicalchargecycleareshowninFigure10.Notethat
thesewaveformsarenottoscaleanddonotrepresentthe
completerangeofpossibleactivity.Thefigureissimply
intendedtoallowbetterconceptualunderstandingandto
highlighttherelativebehaviorofcertainsignalsgenerated
bytheLTC4011duringatypicalchargecycle.
Initially,theLTC4011isinlowpowershutdownasthe
systemoperatesfromaheavilydischargedbattery.ADC
adapteristhenconnectedsuchthatVCCrisesabove4.25V
andis500mVaboveBAT.TheREADYoutputisasserted
whentheLTC4011completeschargequalification.
WhentheLTC4011determineschargingshouldbegin,it
startsaprechargecyclebecauseVCELLislessthan900mV.
As long as the temperature remains within prescribed
limits,theLTC4011charges(TGATEswitching),applying
limitedcurrenttothebatterywiththePWMinorderto
bringtheaveragecellvoltageto900mV.
When the precharge state timer expires, the LTC4011
beginsfastchargeifVCELLisgreaterthan900mV.The
PWM,chargetimerandinternalterminationcontrolare
suspendedifpauseisasserted(VTEMP<200mV),butall
statusoutputscontinuetoindicatechargingisinprogress.
Thefastchargestatecontinuesuntiltheselectedvoltage
ortemperatureterminationcriteriaaremet.Figure10sug-
geststerminationbasedon∆T/∆t,whichforNiMHwould
beanincreasegreaterthan1°Cperminute.
BecauseNiMHchargingterminateddueto∆T/∆tandthe
fastchargecyclehadlastedmorethantMAX/12minutes,
theLTC4011beginsatop-offchargewithacurrentof
IPROG/10.Top-offisaninternallytimedchargeoftMAX/3
minuteswiththeCHRGandTOCoutputscontinuously
asserted.
Finally,theLTC4011enterstheautomaticrechargestate
wheretheCHRGandTOCoutputsaredeasserted.The
PWMisdisabledbutVCDIVremainsassertedtomonitor
VCELL.Thechargetimerwillberesetandfastchargingwill
resumeifVCELLdropsbelow1.325V.TheLTC4011enters
shutdownwhentheDCadapterisremoved,minimizing
currentdrawfromthebatteryintheabsenceofaninput
powersource.
WhilenotapartofthesamplewaveformsofFigure10,
temperaturequalificationisanongoingpartofthecharg-
ingprocess,ifanexternalthermistornetworkisdetected
bytheLTC4011.Shouldprescribedtemperaturelimitsbe
exceededduringanyparticularchargingstate,charging
wouldbesuspendeduntilthesensedtemperaturereturned
toanacceptablerange.
Battery-ControlledCharging
BecauseoftheprogrammingarrangementoftheLTC4011,
itmaybepossibletoconfigureitforbattery-controlled
charging.Inthiscase,thebatterypackisdesignedto
providecustomizedinformationtoanLTC4011-based
charger,allowingasingledesigntoserviceawiderange
ofapplicationbatteries.Assumethechargerisdesigned
toprovideamaximumchargecurrentof800mA(RSENSE=
125mΩ).Figure11showsa4-cellNiCdbatterypackfor
which800mArepresentsa0.75Crate.Whenconnected
tothecharger,thispackwouldprovidebatterytempera-
tureinformationandcorrectlyconfigurebothfastcharge
terminationparametersandtimelimitsfortheinternal
NiCdcells.



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