LM3420-4.2,-8.2,-8.4,-12.6,-16.8Lithium-IonBatteryChargeControllerMay1998
LM3420-4.2,-8.2,-8.4,-12.6,-16.8
Lithium-IonBatteryChargeController
GeneralDescription
TheLM3420seriesofcontrollersaremonolithicintegratedcircuitsdesignedforchargingandend-of-chargecontrolforLithium-Ionrechargeablebatteries.TheLM3420isavailableinfivefixedvoltageversionsforonethroughfourcellchargerapplications(4.2V,8.2V/8.4V,12.6Vand16.8Vrespec-tively).
Includedinaverysmallpackageisan(internallycompen-sated)opamp,abandgapreference,anNPNoutputtransis-tor,andvoltagesettingresistors.Theamplifier’sinvertingin-putisexternallyaccessibleforloopfrequencycompensation.Theoutputisanopen-emitterNPNtransistorcapableofdrivingupto15mAofoutputcurrentintoexternalcircuitry.
Atrimmedprecisionbandgapreferenceutilizestemperaturedriftcurvaturecorrectionforexcellentvoltagestabilityovertheoperatingtemperaturerange.Availablewithaninitialtol-eranceof0.5%fortheAgradeversion,and1%forthestan-dardversion,theLM3420allowsforprecisionend-of-chargecontrolforLithium-Ionrechargeablebatteries.
TheLM3420isavailableinasub-miniature5-leadSOT23-5surfacemountpackagethusallowingverycompactdesigns.
Features
nnnnn
Voltageoptionsforcharging1,2,3or4cellsTinySOT23-5package
Precision(0.5%)end-of-chargecontrolDrivecapabilityforexternalpowerstageLowquiescentcurrent,85µA(typ.)
Applications
nLithium-Ionbatterycharging
nSuitableforlinearandswitchingregulatorchargerdesigns
TypicalApplicationandFunctionalDiagram
DS012359-1
TypicalConstantCurrent/ConstantVoltage
Li-IonBatteryCharger
DS012359-2
LM3420FunctionalDiagram
SIMPLESWITCHER®isaregisteredtrademarkofNationalSemiconductorCorporation.
©1999NationalSemiconductorCorporationDS012359www.national.com
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ConnectionDiagramsandOrderInformation
5-LeadSmallOutlinePackage(M5)
ActualSize
DS012359-3
*Nointernalconnection,butshouldbesolderedtoPCboardforbestheattransfer.
TopView
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AbsoluteMaximumRatings(Note1)
IfMilitary/Aerospacespecifieddevicesarerequired,pleasecontacttheNationalSemiconductorSalesOffice/Distributorsforavailabilityandspecifications.InputVoltageV(IN)OutputCurrent
JunctionTemperatureStorageTemperatureLeadTemperature
VaporPhase(60seconds)Infrared(15seconds)
PowerDissipation(TA=25˚C)(Note2)
20V20mA150˚C
−65˚Cto+150˚C
+215˚C+220˚C300mW
ESDSusceptibility(Note3)HumanBodyModel1500VSeeAN-450“SurfaceMountingMethodsandTheirEffectonProductReliability”formethodsonsolderingsurface-mountdevices.
OperatingRatings(Notes1,2)
AmbientTemperatureRangeJunctionTemperatureRangeOutputCurrent
−40˚C≤TA≤+85˚C−40˚C≤TJ≤+125˚C
15mA
LM3420-4.2
ElectricalCharacteristics
SpecificationswithstandardtypefaceareforTJ=25˚C,andthosewithboldfacetypeapplyoverfullOperatingTempera-tureRange.Unlessotherwisespecified,V(IN)=VREG,VOUT=1.5V.Symbol
Parameter
Conditions
Typical(Note4)
VREGRegulationVoltage
IOUT=1mA
4.2
4.221/4.2424.179/4.158
RegulationVoltageTolerance
IqGmQuiescentCurrentTransconductance∆IOUT/∆VREGIOUT=1mA20µA≤IOUT≤1mAVOUT=2V
1mA≤IOUT≤15mAVOUT=2V
AVVoltageGain∆VOUT/∆VREG1V≤VOUT≤VREG−1.2V(−1.3)RL=200Ω(Note6)
1V≤VOUT≤VREG−1.2V(−1.3)RL=2kΩ
V(IN)=VREG+100mVIOUT=15mA
V(IN)=VREG−100mVVOUT=0V
85
110/115
3.3
1.3/0.75
6.0
3.0/1.5
1000
550/250
3500
1500/900
1.0
1.2/1.3
0.1
0.5/1.0
75
9456
EnOutputNoiseVoltage
IOUT=1mA,10Hz≤f≤10kHz
70
94560.5/1.01.2/1.31000/700450/2002.5/1.41.0/0.50125/150
µAµA(max)mA/mVmA/mV(min)mA/mVmA/mV(min)
V/VV/V(min)V/VV/V(min)
VV(max)µAµA(max)kΩkΩ(max)kΩ(min)µVRMSIOUT=1mA
4.242/4.2844.158/4.116
LM3420A-4.2
Limit(Note5)
LM3420-4.2
Limit(Note5)
VV(max)V(min)%(max)Units(Limits)
±0.5/±1±1/±2
VSATILRfOutputSaturation(Note7)OutputLeakageCurrent
InternalFeedbackResistor(Note8)
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LM3420-8.2
ElectricalCharacteristics
SpecificationswithstandardtypefaceareforTJ=25˚C,andthosewithboldfacetypeapplyoverfullOperatingTempera-tureRange.Unlessotherwisespecified,V(IN)=VREG,VOUT=1.5V.Symbol
Parameter
Conditions
Typical(Note4)
VREGRegulationVoltage
IOUT=1mA
8.2
8.241/8.2828.159/8.118
RegulationVoltageTolerance
IqGmQuiescentCurrentTransconductance∆IOUT/∆VREGIOUT=1mA20µA≤IOUT≤1mAVOUT=6V
1mA≤IOUT≤15mAVOUT=6V
AVVoltageGain∆VOUT/∆VREG1V≤VOUT≤VREG−1.2V(−1.3)RL=470Ω(Note6)
1V≤VOUT≤VREG−1.2V(−1.3)RL=5kΩ
V(IN)=VREG+100mVIOUT=15mA
V(IN)=VREG−100mVVOUT=0V
85
110/115
3.3
1.3/0.75
6.0
3.0/1.5
1000
550/250
3500
1500/900
1.0
1.2/1.3
0.1
0.5/1.0
176
220132
EnOutputNoiseVoltage
IOUT=1mA,10Hz≤f≤10kHz
140
2201320.5/1.01.2/1.31000/700450/2002.5/1.41.0/0.50125/150
µAµA(max)mA/mVmA/mV(min)mA/mVmA/mV(min)
V/VV/V(min)V/VV/V(min)
VV(max)µAµA(max)kΩkΩ(max)kΩ(min)µVRMSIOUT=1mA
8.282/8.3648.118/8.036
LM3420A-8.2
Limit(Note5)
LM3420-8.2
Limit(Note5)
VV(max)V(min)%(max)Units(Limits)
±0.5/±1±1/±2
VSATILRfOutputSaturation(Note7)OutputLeakageCurrent
InternalFeedbackResistor(Note8)
LM3420-8.4
ElectricalCharacteristics
SpecificationswithstandardtypefaceareforTJ=25˚C,andthosewithboldfacetypeapplyoverfullOperatingTempera-tureRange.Unlessotherwisespecified,V(IN)=VREG,VOUT=1.5V.Symbol
Parameter
Conditions
Typical(Note4)
VREGRegulationVoltage
IOUT=1mA
8.4
8.442/8.4848.358/8.316
RegulationVoltageTolerance
IqGmQuiescentCurrentTransconductance∆IOUT/∆VREGIOUT=1mA20µA≤IOUT≤1mAVOUT=6V
1mA≤IOUT≤15mAVOUT=6V
85
110/115
3.3
1.3/0.75
6.0
3.0/1.5
2.5/1.41.0/0.50125/150
µAµA(max)mA/mVmA/mV(min)mA/mVmA/mV(min)
IOUT=1mA
8.484/8.5688.316/8.232
LM3420A-8.4
Limit(Note5)
LM3420-8.4
Limit(Note5)
VV(max)V(min)%(max)Units(Limits)
±0.5/±1±1/±2
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LM3420-8.4
ElectricalCharacteristics
Symbol
Parameter
(Continued)
SpecificationswithstandardtypefaceareforTJ=25˚C,andthosewithboldfacetypeapplyoverfullOperatingTempera-tureRange.Unlessotherwisespecified,V(IN)=VREG,VOUT=1.5V.
Conditions
Typical(Note4)
AVVoltageGain∆VOUT/∆VREG1V≤VOUT≤VREG−1.2V(−1.3)RL=470Ω(Note6)
1V≤VOUT≤VREG−1.2V(−1.3)RL=5kΩ
V(IN)=VREG+100mVIOUT=15mA
V(IN)=VREG−100mVVOUT=0V
1000
550/250
3500
1500/900
1.0
1.2/1.3
0.1
0.5/1.0
181
227135
EnOutputNoiseVoltage
IOUT=1mA,10Hz≤f≤10kHz
140
2271350.5/1.01.2/1.31000/700450/200
LM3420A-8.4
Limit(Note5)
LM3420-8.4
Limit(Note5)
V/VV/V(min)V/VV/V(min)
VV(max)µAµA(max)kΩkΩ(max)kΩ(min)µVRMSUnits(Limits)
VSATILRfOutputSaturation(Note7)OutputLeakageCurrent
InternalFeedbackResistor(Note8)
LM3420-12.6
ElectricalCharacteristics
SpecificationswithstandardtypefaceareforTJ=25˚C,andthosewithboldfacetypeapplyoverfullOperatingTemperatureRange.Unlessotherwisespecified,V(IN)=VREG,VOUT=1.5V.Symbol
Parameter
Conditions
Typical(Note4)
VREGRegulationVoltage
IOUT=1mA
12.6
12.663/12.72612.537/12.474
RegulationVoltageTolerance
IqGmQuiescentCurrentTransconductance∆IOUT/∆VREGIOUT=1mA20µA≤IOUT≤1mAVOUT=10V
1mA≤IOUT≤15mAVOUT=10V
AVVoltageGain∆VOUT/∆VREG1V≤VOUT≤VREG−1.2V(−1.3)RL=750Ω(Note6)
1V≤VOUT≤VREG−1.2V(−1.3)RL=10kΩ
V(IN)=VREG+100mVIOUT=15mA
V(IN)=VREG−100mVVOUT=0V
85
110/115
3.3
1.3/0.75
6.0
3.0/1.5
1000
550/250
3500
1500/900
1.0
1.2/1.3
0.1
0.5/1.0
287
359215
EnOutputNoiseVoltage
IOUT=1mA,10Hz≤f≤10kHz
210
3592150.5/1.01.2/1.31000/700450/2002.5/1.41.0/0.5125/150
µAµA(max)mA/mVmA/mV(min)mA/mVmA/mV(min)
V/VV/V(min)V/VV/V(min)
VV(max)µAµA(max)kΩkΩ(max)kΩ(min)µVRMSIOUT=1mA
12.726/12.85212.474/12.348
LM3420A-12.6
Limit(Note5)
LM3420-12.6
Limit(Note5)
VV(max)V(min)%(max)Units(Limits)
±0.5/±1±1/±2
VSATILRfOutputSaturation(Note7)OutputLeakageCurrent
InternalFeedbackResistor(Note8)
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LM3420-16.8
ElectricalCharacteristics
SpecificationswithstandardtypefaceareforTJ=25˚C,andthosewithboldfacetypeapplyoverfullOperatingTemperatureRange.Unlessotherwisespecified,V(IN)=VREG,VOUT=1.5V.Symbol
Parameter
Conditions
Typical(Note4)
VREGRegulationVoltage
IOUT=1mA
16.8
16.884/16.96816.716/16.632
RegulationVoltageTolerance
IqGmQuiescentCurrentTransconductance∆IOUT/∆VREGIOUT=1mA20µA≤IOUT≤1mAVOUT=15V
1mA≤IOUT≤15mAVOUT=15V
AVVoltageGain∆VOUT/∆VREG1V≤VOUT≤VREG−1.2V(−1.3)RL=1kΩ(Note6)
1V≤VOUT≤VREG−1.2V(−1.3)RL=15kΩ
V(IN)=VREG+100mVIOUT=15mA
V(IN)=VREG−100mVVOUT=0V
85
110/115
3.3
0.8/0.4
6.0
2.9/0.9
1000
550/250
3500
1200/750
1.0
1.2/1.3
0.1
0.5/1.0
392
490294
EnOutputNoiseVoltage
IOUT=1mA,10Hz≤f≤10kHz
280
4902940.5/1.01.2/1.31000/650450/2002.5/0.750.7/0.35125/150
µAµA(max)mA/mVmA/mV(min)mA/mVmA/mV(min)
V/VV/V(min)V/VV/V(min)
VV(max)µAµA(max)kΩkΩ(max)kΩ(min)µVRMSIOUT=1mA
16.968/17.13616.632/16.464
LM3420A-16.8
Limit(Note5)
LM3420-16.8
Limit(Note5)
VV(max)V(min)%(max)Units(Limits)
±0.5/±1±1/±2
VSATILRfOutputSaturation(Note7)OutputLeakageCurrent
InternalFeedbackResistor(Note8)
Note1:AbsoluteMaximumRatingsindicatelimitsbeyondwhichdamagetothedevicemayoccur.OperatingRatingsindicateconditionsforwhichthedeviceisin-tendedtobefunctional,butdonotguaranteespecificperformancelimits.Forguaranteedspecificationsandtestconditions,seetheElectricalCharacteristics.Theguaranteedspecificationsapplyonlyforthetestconditionslisted.Someperformancecharacteristicsmaydegradewhenthedeviceisnotoperatedunderthelistedtestconditions.
Note2:ThemaximumpowerdissipationmustbederatedatelevatedtemperaturesandisdictatedbyTJmax(maximumjunctiontemperature),θJA(junctiontoam-bientthermalresistance),andTA(ambienttemperature).ThemaximumallowablepowerdissipationatanytemperatureisPDmax=(TJmax−TA)/θJAorthenumbergivenintheAbsoluteMaximumRatings,whicheverislower.Thetypicalthermalresistance(θJA)whensolderedtoaprintedcircuitboardisapproximately306˚C/WfortheM5package.
Note3:Thehumanbodymodelisa100pFcapacitordischargedthrougha1.5kΩresistorintoeachpin.Note4:Typicalnumbersareat25˚Candrepresentthemostlikelyparametricnorm.
Note5:Limitsare100%productiontestedat25˚C.LimitsovertheoperatingtemperaturerangeareguaranteedthroughcorrelationusingStatisticalQualityControl(SQC)methods.ThelimitsareusedtocalculateNational’sAveragingOutgoingQualityLevel(AOQL).Note6:Actualtestisdoneusingequivalentcurrentsinkinsteadofaresistorload.
Note7:VSAT=V(IN)−VOUT,whenthevoltageattheINpinisforced100mVabovethenominalregulatingvoltage(VREG).Note8:SeeApplicationsandTypicalPerformanceCharacteristicssectionsforinformationonthisresistor.
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TypicalPerformanceCharacteristics
4.2V
BodePlot
ResponseTimefor4.2VVersion
ResponseTimefor4.2VVersion
DS012359-17DS012359-18DS012359-19
8.2Vand8.4VBodePlotResponseTimefor8.2V,8.4VVersionsResponseTimefor8.2V,8.4VVersions
DS012359-20DS012359-21DS012359-22
12.6V
BodePlotResponseTimefor12.6VVersionResponseTimefor12.6VVersion
DS012359-23DS012359-24DS012359-25
16.8V
BodePlotResponseTimefor16.8VVersionResponseTimefor16.8VVersion
DS012359-26DS012359-27DS012359-28
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TypicalPerformanceCharacteristics
RegulationVoltagevsOutputVoltageandLoadResistance
(Continued)
CircuitUsedforResponseTime
CircuitUsedforBodePlots
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RegulationVoltagevsOutputVoltageandLoadResistance
QuiescentCurrent
InternalFeedbackResistor(Rf)Tempco
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DS012359-32DS012359-34
RegulationVoltagevsOutputVoltageandLoadResistance
Normalized
TemperatureDrift
OutputSaturationVoltage(VSAT)
DS012359-36
DS012359-35
DS012359-37
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TypicalPerformanceCharacteristics
RegulationVoltagevsOutputVoltageandLoadResistance
(Continued)
DS012359-38
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FiveLeadSurfaceMountPackageInformation
ThesmallSOT23-5packageallowsonly4alphanumericcharacterstoidentifytheproduct.Thetablebelowcontainsthefieldin-formationmarkedonthepackage.
Voltage4.2V4.2V4.2V4.2V8.2V8.2V8.2V8.2V8.4V8.4V8.4V8.4V12.6V12.6V12.6V12.6V16.8V16.8V16.8V16.8V
GradeA(Prime)A(Prime)B(Standard)B(Standard)A(Prime)A(Prime)B(Standard)B(Standard)A(Prime)A(Prime)B(Standard)B(Standard)A(Prime)A(Prime)B(Standard)B(Standard)A(Prime)A(Prime)B(Standard)B(Standard)
OrderInformationLM3420AM5-4.2LM3420AM5X-4.2LM3420M5-4.2LM3420M5X-4.2LM3420AM5-8.2LM3420AM5X-8.2LM3420M5-8.2LM3420M5X-8.2LM3420AM5-8.4LM3420AM5X-8.4LM3420M5-8.4LM3420M5X-8.4LM3420AM5-12.6LM3420AM5X-12.6LM3420M5-12.6LM3420M5X-12.6LM3420AM5-16.8LM3420AM5X-16.8LM3420M5-16.8LM3420M5X-16.8
PackageMarkingD02AD02AD02BD02BD07AD07AD07BD07BD03AD03AD03BD03BD04AD04AD04BD04BD05AD05AD05BD05B
250unitincrementsontapeandreel3kunitincrementsontapeandreel250unitincrementsontapeandreel3kunitincrementsontapeandreel250unitincrementsontapeandreel3kunitincrementsontapeandreel250unitincrementsontapeandreel3kunitincrementsontapeandreel250unitincrementsontapeandreel3kunitincrementsontapeandreel250unitincrementsontapeandreel3kunitincrementsontapeandreel250unitincrementsontapeandreel3kunitincrementsontapeandreel250unitincrementsontapeandreel3kunitincrementsontapeandreel250unitincrementsontapeandreel3kunitincrementsontapeandreel250unitincrementsontapeandreel3kunitincrementsontapeandreel
Suppliedas
FIGURE1.SOT23-5Marking
Thefirstletter“D”identifiesthepartasaDriver,thenexttwonumbersindicatethevoltage,“02”fora4.2Vpart,“07”foran8.2Vpart,“03”foran8.4Vpart,“04”fora12.6Vpart,and“05”fora16.8Vpart.Thefourthletterindicatesthegrade,“B”forstandardgrade,“A”fortheprimegrade.
TheSOT23-5surfacemountpackageisonlyavailableontapeinquantityincrementsof250ontapeandreel(indicatedbytheletters“M5”inthepartnumber),orinquantityincrementsof3000ontapeandreel(indicatedbytheletters“M5X”inthepartnum-ber).
ProductDescription
TheLM3420isashuntregulatorspecificallydesignedtobethereferenceandcontrolsectioninanoverallfeedbackloopofaLithium-Ionbatterycharger.Theregulatedoutputvolt-ageissensedbetweentheINpinandGROUNDpinoftheLM3420.IfthevoltageattheINpinislessthantheLM3420regulatingvoltage(VREG),theOUTpinsourcesnocurrent.AsthevoltageattheINpinapproachestheVREGvoltage,theOUTpinbeginssourcingcurrent.Thiscurrentisthenusedtodriveafeedbackdevice(opto-coupler),orapowerdevice(linearregulator,switchingregulator,etc.),whichser-vostheoutputvoltagetobethesamevalueasVREG.Insomeapplications,(evenundernormaloperatingcondi-tions)thevoltageontheINpincanbeforcedabovetheVREGvoltage.Intheseinstances,themaximumvoltageap-pliedtotheINpinshouldnotexceed20V.Inaddition,anex-ternalresistormayberequiredontheOUTpintolimitthemaximumcurrentto20mA.
singlecapacitor(CC)connectedfromthecompensationpintotheoutpinoftheLM3420.Thecapacitorvaluesshownintheschematicsareadequateundermostconditions,buttheycanbeincreasedordecreaseddependingonthede-siredloopresponse.Applyingaloadpulsetotheoutputofaregulatorcircuitandobservingtheresultantoutputvoltageresponseisaneasymethodofdeterminingthestabilityofthecontrolloop.
Analyzingmorecomplexfeedbackloopsrequiresadditionalinformation.
TheformulaforACgainatafrequency(f)isasfollows;
Compensation
Theinvertinginputoftheerroramplifierisbroughtouttoal-lowoverallclosed-loopcompensation.Inmanyoftheappli-cationscircuitsshownhere,compensationisprovidedbya
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whereRf≈75kΩforthe4.2Vpart,Rf≈181kΩforthe8.4Vpart,Rf≈287kΩforthe12.6Vpart,andRf≈392kΩforthe16.8Vpart.
Theresistor(Rf)intheformulaisaninternalresistorlocatedonthedie.Sincethisresistorvaluewillaffectthephasemar-gin,theworstcasemaximumandminimumvaluesareim-
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Compensation
(Continued)
TestCircuit
ThetestcircuitshowninFigure2canbeusedtomeasureandverifyvariousLM3420parameters.TestconditionsaresetbyforcingtheappropriatevoltageattheVOUTSettestpointandselectingtheappropriateRLorIOUTasspecifiedintheElectricalCharacteristicssection.UseaDVMatthe“measure”testpointstoreadthedata.
portantwhenanalyzingclosedloopstability.TheminimumandmaximumroomtemperaturevaluesofthisresistorarespecifiedintheElectricalCharacteristicssectionofthisdatasheet,andacurveshowingthetemperaturecoefficientisshowninthecurvessection.MinimumvaluesofRfresultinlowerphasemargins.
DS012359-7
FIGURE2.LM3420TestCircuit
VREGExternalVoltageTrim
Theregulationvoltage(VREG)oftheLM3420canbeexter-nallytrimmedbyaddingasingleresistorfromtheCOMPpintothe+INpinorfromtheCOMPpintotheGNDpin,depend-ingonthedesiredtrimdirection.Trimadjustmentsupto±10%ofVREGcanberealized,withonlyasmallincreaseinthetemperaturecoefficient.(SeetemperaturecoefficientcurveshowninFigure3below.)
DS012359-9
IncreasingVREGDS012359-10
DecreasingVREGFIGURE4.ChangingVREGFormulasforselectingtrimresistorvaluesareshownbelow,basedonthepercentofincrease(%incr)orpercentofde-crease(%decr)oftheoutputvoltagefromthenominalvolt-age.
ForLM3420-4.2
Rincrease=22x105/%incr
Rdecrease=(53x105/%decr)−75x103ForLM3420-8.2
11
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DS012359-8
NormalizedTemperatureDriftwith
OutputExternallyTrimmed
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VREGExternalVoltageTrim
ForLM3420-8.4
(Continued)
Rincrease=26x105/%incr
Rdecrease=(150x105/%decr)−176x103Rincrease=26x105/%incr
Rdecrease=(154x105/%decr)−181x103ForLM3420-12.6
Rincrease=28x105/%incr
Rdecrease=(259x105/%decr)−287x103ForLM3420-16.8
Rincrease=29x105/%incr
Rdecrease=(364x105/%decr)−392x103cuitsshownaredesignedfor2celloperation,buttheycanreadilybechangedforeither1,3or4cellchargingapplica-tions.
OneitemtokeepinmindwhendesigningwiththeLM3420isthatthereareparasiticdiodespresent.Insomedesigns,un-derspecialelectricalconditions,unwantedcurrentsmayflow.ParasiticdiodesexistfromOUTtoIN,aswellasfromGROUNDtoIN.InbothinstancesthediodearrowispointedtowardtheINpin.
ApplicationCircuits
ThecircuitshowninFigure5performsconstant-current,constant-voltagechargingoftwoLi-Ioncells.Atthebegin-ningofthechargecycle,whenthebatteryvoltageislessthan8.4V,theLM3420sourcesnocurrentfromtheOUTpin,keepingQ2off,thusallowingtheLM317Adjustablevoltageregulatortooperateasaconstant-currentsource.(TheLM317isratedforcurrentsupto1.5A,andtheLM350andLM338canbeusedforhighercurrents.)TheLM317forcesaconstant1.25VacrossRLIM,thusgeneratingaconstantcurrentof
ILIM=1.25V/RLIMApplicationInformation
TheLM3420regulator/driverprovidesthereferenceandfeedbackdrivefunctionsforaLithium-Ionbatterycharger.ItcanbeusedinmanydifferentchargerconfigurationsusingbothlinearandswitchingtopologiestoprovidetheprecisionneededforchargingLithium-Ionbatteriessafelyandeffi-ciently.Outputvoltagetolerancesbetterthan0.5%arepos-siblewithoutusingtrimpotsorprecisionresistors.Thecir-
DS012359-1
FIGURE5.ConstantCurrent/ConstantVoltageLi-IonBatteryCharger
DS012359-11
FIGURE6.LowDrop-OutConstantCurrent/ConstantVoltage2-CellCharger
TransistorQ1providesadisconnectbetweenthebatteryandtheLM3420whentheinputvoltageisremoved.Thispreventsthe85µAquiescentcurrentoftheLM3420fromeventuallydischargingthebattery.InthisapplicationQ1isusedasalowoffsetsaturatedswitch,withthemajorityofthebasedrivecurrentflowingthroughthecollectorandcrossingovertotheemitterasthebatterybecomesfullycharged.Itprovidesaverylowcollectortoemittersaturationvoltage
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(approximately5mV).DiodeD1isalsousedtopreventthebatterycurrentfromflowingthroughtheLM317regulatorfromtheoutputtotheinputwhentheDCinputvoltageisre-moved.
Asthebatterycharges,itsvoltagebeginstorise,andissensedattheINpinoftheLM3420.Oncethebatteryvoltagereaches8.4V,theLM3420beginstoregulateandstartssourcingcurrenttothebaseofQ2.TransistorQ2begins
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ApplicationCircuits
(Continued)
controllingtheADJ.pinoftheLM317whichbeginstoregu-latethevoltageacrossthebatteryandtheconstantvoltageportionofthechargingcyclestarts.Oncethechargerisintheconstantvoltagemode,thechargermaintainsaregu-lated8.4Vacrossthebatteryandthechargingcurrentisde-pendentonthestateofchargeofthebattery.Asthecellsap-proachafullychargedcondition,thechargecurrentfallstoaverylowvalue.
stageoftheLM10Cwilldisconnectthebatteryfromthechargercircuitwhentheinputsupplyvoltageisremovedtopreventthebatteryfromdischarging.
Figure6showsaLi-Ionbatterychargerthatfeaturesadrop-outvoltageoflessthanonevolt.Thischargerisaconstant-current,constant-voltagecharger(itoperatesinconstant-currentmodeatthebeginningofthechargecycleandswitchesovertoaconstant-voltagemodeneartheendofthechargingcycle).Thecircuitconsistsoftwobasicfeed-backloops.Thefirstloopcontrolstheconstantchargecur-rentdeliveredtothebattery,andtheseconddeterminesthefinalvoltageacrossthebattery.
Withadischargedbatteryconnectedtothecharger,(batteryvoltageislessthan8.4V)thecircuitbeginsthechargecyclewithaconstantchargecurrent.ThevalueofthiscurrentissetbyusingthereferencesectionoftheLM10Ctoforce200mVacrossR7thuscausingapproximately100µAofemittercurrenttoflowthroughQ1,andapproximately1mAofemit-tercurrenttoflowthroughQ2.ThecollectorcurrentofQ1isalsoapproximately100µA,andthiscurrentflowsthroughR2developing50mVacrossit.This50mVisusedasaref-erencetodeveloptheconstantchargecurrentthroughthecurrentsenseresistorR1.
Theconstantcurrentfeedbackloopoperatesasfollows.Ini-tially,theemitterandcollectorcurrentofQ2arebothap-proximately1mA,thusprovidinggatedrivetotheMOSFETQ3,turningiton.TheoutputoftheLM301Aop-ampislow.AsQ3’scurrentreaches1A,thevoltageacrossR1ap-proaches50mV,thuscancelingthe50mVdropacrossR2,andcausingtheop-amp’soutputtostartgoingpositive,andbeginsourcingcurrentintoR8.AsmorecurrentisforcedintoR8fromtheop-amp,thecollectorcurrentofQ2isreducedbythesameamount,whichdecreasesthegatedrivetoQ3,tomaintainaconstant50mVacrossthe0.05Ωcurrentsens-ingresistor,thusmaintainingaconstant1Aofchargecur-rent.
ThecurrentlimitloopisstabilizedbycompensatingtheLM301AwithC1(thestandardfrequencycompensationusedwiththisop-amp)andC2,whichisadditionalcompen-sationneededwhenD3isforwardbiased.ThishelpsspeeduptheresponsetimeduringthereversebiasofD3.WhentheLM301Aoutputislow,diodeD3reversebiasesandpre-ventstheop-ampfrompullingmorecurrentthroughtheemit-terofQ2.Thisisimportantwhenthebatteryvoltagereaches8.4V,andthe1Achargecurrentisnolongerneeded.Resis-torR5isolatestheLM301AfeedbacknodeattheemitterofQ2.
Thebatteryvoltageissensedandbufferedbytheop-ampsectionoftheLM10C,connectedasavoltagefollowerdriv-ingtheLM3420.Whenthebatteryvoltagereaches8.4V,theLM3420willbeginregulatingbysourcingcurrentintoR8,whichcontrolsthecollectorcurrentofQ2,whichinturnre-ducesthegatevoltageofQ3andbecomesaconstantvolt-ageregulatorforchargingthebattery.ResistorR6isolatestheLM3420fromthecommonfeedbacknodeattheemitterofQ2.IfR5andR6areomitted,oscillationscouldoccurdur-ingthetransitionfromtheconstant-currenttotheconstant-voltagemode.D2andthePNPtransistorinput
DS012359-12
FIGURE7.HighEfficiencySwitchingRegulatorConstantCurrent/ConstantVoltage2-CellCharger
DS012359-13
FIGURE8.LowDropoutConstantCurrent/Constant
VoltageLi-IonBatteryChargerAswitchingregulator,constant-current,constant-voltagetwo-cellLi-IonbatterychargingcircuitisshowninFigure7.Thiscircuitprovidesmuchbetterefficiency,especiallyoverawideinputvoltagerangethanthelineartopologies.Fora1AchargeranLM2575-ADJ.switchingregulatorICisusedinastandardbucktopology.Forothercurrents,orotherpack-ages,othermembersoftheSIMPLESWITCHER™buckregulatorfamilymaybeused.
Circuitoperationisasfollows.Withadischargedbatteryconnectedtothecharger,thecircuitoperatesasaconstantcurrentsource.Theconstant-currentportionofthechargerisformedbytheloopconsistingofonehalfoftheLM358opampalongwithgainsettingresistorsR3andR4,currentsensingresistorR5,andthefeedbackreferencevoltageof1.23V.InitiallytheLM358’soutputislowcausingtheoutputoftheLM2575-ADJ.torisethuscausingsomechargingcur-renttoflowintothebattery.Whenthecurrentreaches1A,itissensedbyresistorR5(50mΩ),andproduces50mV.This50mVisamplifiedbytheop-ampsgainof25toproduce
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ApplicationCircuits
(Continued)
1.23V,whichisappliedtothefeedbackpinoftheLM2575-ADJ.tosatisfythefeedbackloop.
Oncethebatteryvoltagereaches8.4V,theLM3420takesoverandbeginstocontrolthefeedbackpinoftheLM2575-ADJ.TheLM3420nowregulatesthevoltageacrossthebattery,andthechargerbecomesaconstant-voltagecharger.LoopcompensationnetworkR6andC3ensurestableoperationofthechargercircuitunderbothconstant-currentandconstant-voltageconditions.Iftheinputsupplyvoltageisremoved,diodeD2andthePNPinputstageoftheLM358becomereversedbiasedanddiscon-nectsthebatterytoensurethatthebatteryisnotdischarged.DiodeD3reversebiasestopreventtheop-ampfromsinkingcurrentwhenthechargerchangestoconstantvoltagemode.Theminimumsupplyvoltageforthischargerisapproxi-mately11V,andthemaximumisaround30V(limitedbythe32VmaximumoperatingvoltageoftheLM358).Ifanotherop-ampissubstitutedfortheLM358,makesurethatthein-putcommon-moderangeoftheop-ampextendsdowntogroundsothatitcanaccuratelysense50mV.R1isincludedtoprovideaminimumloadfortheswitchingregulatortoas-surethatswitchleakagecurrentwillnotcausetheoutputtorisewhenthebatteryisremoved.
ThecircuitinFigure8isverysimilartoFigure7,excepttheswitchingregulatorhasbeenreplacedwithalowdropoutlin-earregulator,allowingtheinputvoltagetobeaslowas10V.Theconstantcurrentandconstantvoltagecontrolloopsarethesameasthepreviouscircuit.DiodeD2hasbeenchangedtoaSchottkydiodetoprovideareductionintheoveralldropoutvoltageofthiscircuit,butSchottkydiodestypicallyhavehigherleakagecurrentsthanastandardsili-condiode.Thisleakagecurrentcoulddischargethebatteryiftheinputvoltageisremovedforanextendedperiodoftime.
Anothervariationofaconstantcurrent/constantvoltageswitchmodechargerisshowninFigure9.Thebasicfeed-backloopsforcurrentandvoltagearesimilartothepreviouscircuits.Thiscircuithasthecurrentsensingresistor,fortheconstantcurrentpartofthefeedbackloop,onthepositivesideofthebattery,thusallowingacommongroundbetweentheinputsupplyandthebattery.Also,theLMC7101op-ampisavailableinaverysmallSOT23-5packagethusallowingaverycompactpcboarddesign.DiodeD4preventsthebat-teryfromdischargingthroughthechargercircuitryiftheinputvoltageisremoved,althoughthequiescentcurrentoftheLM3420willstillbepresent(approximately85µA).
DS012359-14
FIGURE9.HighEfficiencySwitchingCharger
withHighSideCurrentSensing
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ApplicationCircuits
(Continued)
DS012359-15
FIGURE10.(Fast)PulsedConstantCurrent2-CellCharger
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ApplicationCircuits
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ArapidchargeLithium-IonbatterychargingcircuitisshowninFigure10.Thisconfigurationusesaswitchingregulatortodeliverthechargingcurrentinaseriesofconstantcurrentpulses.Atthebeginningofthechargecycle(constant-currentmode),thiscircuitperformsidenticallytothepreviousLM2575chargerbychargingthebatteryataconstantcurrentof1A.Asthebatteryvoltagereaches8.4V,thischargerchangesfromaconstantcontinuouscurrentof1Atoa5secondpulsed1A.Thisallowsthetotalbatterychargetimetobereducedconsiderably.Thisisdifferentfromtheotherchargingcircuitsthatswitchfromaconstantcurrentchargetoaconstantvoltagechargeoncethebatteryvoltagereaches8.4V.Afterchargingthebatterywith1Afor5seconds,thechargestops,andthebatteryvoltagebeginstodrop.Whenitdropsbelow8.4V,theLM555timeragainstartsthetimingcycleandchargesthebatterywith1Aforan-other5seconds.Thiscyclingcontinueswithaconstant5secondchargetime,andavariableofftime.Inthismanner,thebatterywillbechargedwith1Afor5seconds,followedbyanoffperiod(determinedbythebattery’sstateofcharge),settingupaperiodic1Achargecurrent.Theofftimeisdeter-minedbyhowlongittakesthebatteryvoltagetodecreasebackdownto8.4V.Whenthebatteryfirstreaches8.4V,the
offtimewillbeveryshort(1msorless),butwhenthebatteryapproachesfullcharge,theofftimewillbeginincreasingtotensofseconds,thenminutes,andeventuallyhours.
Theconstant-currentloopforthischargerandthemethodusedforprogrammingthe1AconstantcurrentisidenticaltothepreviousLM2575-ADJ.charger.Inthiscircuit,asecondLM3420-8.4hasitsVREGincreasedbyapproximately400mV(viaR2),andisusedtolimittheoutputvoltageofthechargerto8.8Vintheeventofabadbatteryconnection,orthebatteryisremovedorpossiblydamaged.
TheLM555timerisconnectedasaone-shot,andisusedtoprovidethe5secondchargingpulses.Aslongasthebatteryvoltageislessthanthe8.4V,theoutputofIC3willbeheldlow,andtheLM555one-shotwillneverfire(theoutputoftheLM555willbeheldhigh)andtheone-shotwillhavenoeffectonthecharger.Oncethebatteryvoltageexceedsthe8.4VregulationvoltageofIC3,thetriggerpinoftheLM555ispulledhigh,enablingtheoneshottobegintiming.Thechargecurrentwillnowbepulsedintothebatteryata5sec-ondrate,withtheofftimedeterminedbythebattery’sstateofcharge.TheLM555outputwillgohighfor5seconds(pull-ingdownthecollectorofQ1)whichallowsthe1Aconstant-currentlooptocontrolthecircuit.
DS012359-16
FIGURE11.MOSFETLowDropoutCharger
Figure11showsalowdropoutconstantvoltagechargerus-ingaMOSFETasthepasselement,butthiscircuitdoesnotincludecurrentlimiting.ThiscircuitusesQ3andaSchottkydiodetoisolatethebatteryfromthechargingcircuitrywhentheinputvoltageisremoved,topreventthebatteryfromdis-charging.Q2shouldbeahighcurrent(0.2Ω)FET,whileQ3canbealowcurrent(2Ω)device.
Note:Althoughtheapplicationcircuitsshownherehavebeenbuiltandtested,theyshouldbethoroughlyevalu-atedwiththesametypeofbatterythechargerwilleven-tuallybeusedwith.
Differentbatterymanufacturersmayuseaslightlydif-ferentbatterychemistrywhichmayrequiredifferentchargingcharacteristics.Alwaysconsultthebatterymanufacturerforinformationonchargingspecificationsandbatterydetails,andalwaysobservethemanufactur-ersprecautionswhenusingtheirbatteries.Avoidover-chargingorshortingLithium-Ionbatteries.
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LM3420-4.2,-8.2,-8.4,-12.6,-16.8Lithium-IonBatteryChargeControllerPhysicalDimensions
inches(millimeters)unlessotherwisenoted
5-LeadSmallOutlinePackage(M5)
ForOrderingInformationSeeFigure1InThisDataSheet
NSPackageNumberMA05B
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