ltc4011 - high efficiency standalone nickel battery charger · vil input voltage low chem (nimh) l...

LTC4011

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Typical applicaTion

FeaTures DescripTion

High Efficiency Standalone Nickel Battery Charger

applicaTions

n CompleteNiMH/NiCdChargerfor1to16Cellsn NoMicrocontrollerorFirmwareRequiredn 550kHzSynchronousPWMCurrentSourceControllern NoAudibleNoisewithCeramicCapacitorsn PowerPath™ControlSupportn ProgrammableChargeCurrent:5%Accuracyn WideInputVoltageRange:4.5Vto34Vn AutomaticTricklePrechargen –∆VFastChargeTerminationn Optional∆T/∆tFastChargeTerminationn AutomaticNiMHTop-OffChargen ProgrammableTimern AutomaticRechargen MultipleStatusOutputsn MicropowerShutdownn 20-LeadThermallyEnhancedTSSOPPackage

n IntegratedorStandaloneBatteryChargern PortableInstrumentsorConsumerProductsn Battery-PoweredDiagnosticsandControln Back-UpBatteryManagementL,LT,LTC,LTM,LinearTechnologyandtheLinearlogoareregisteredtrademarksofLinearTechnologyCorporation.PowerPathisatrademarkofLinearTechnologyCorporation.Allothertrademarksarethepropertyoftheirrespectiveowners.

TheLTC®4011providesacomplete,cost-effectivenickelbatteryfastchargesolutioninasmallpackageusingfewexternal components. A 550kHz PWM current sourcecontrollerandallnecessarychargeinitiation,monitoringandterminationcontrolcircuitryareincluded.

The LTC4011 automatically senses the presence of aDC adapter and battery insertion or removal. Heavilydischarged batteries are precharged with a trickle cur-rent.TheLTC4011cansimultaneouslyuseboth–∆Vand∆T/∆tfastchargeterminationtechniquesandcandetectvariousbattery faults. Ifnecessary, a top-off charge isautomaticallyappliedtoNiMHbatteriesafterfastcharg-ingiscompleted.TheICwillalsoresumechargingifthebatteryself-dischargesafterafullchargecycle.

AllLTC4011chargingoperationsarequalifiedbyactualchargetimeandmaximumaveragecellvoltage.Chargingmayalsobegatedbyminimumandmaximumtemperaturelimits.NiMHorNiCdfastchargeterminationparametersarepin-selectable.

IntegratedPowerPathcontrol supportensures that thesystemremainspoweredatalltimeswithoutallowingloadtransientstoadverselyaffectchargetermination.

2ANiMHBatteryCharger2ANiMHChargeCycleat1C

0.1µF

10µF

4.7µH

10µF

0.033µF 0.068µF

FAULTINFET

CHRG

FROMADAPTER

5V

TOCREADY

LTC4011

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pin conFiguraTionabsoluTe MaxiMuM raTings(Note 1)VCC (Input Supply) to GND......................... –0.3V to 36VDCIN to GND .............................................. –0.3V to 36VFAULT, CHRG, VCELL, VCDIV, SENSE, BAT, TOCor READY to GND ........................... –0.3V to VCC + 0.3VSENSE to BAT ........................................................±0.3VCHEM, VTEMP or TIMER to GND ................ –0.3V to 3.5VPGND to GND .........................................................±0.3VOperating Ambient Temperature Range(Note 2) ........................................................ 0°C to 85°COperating Junction Temperature (Note 3) ............. 125°CStorage Temperature Range ...................–65°C to 150°CLead Temperature (Soldering, 10 sec) .................. 300°C

(Note 4) The l indicates specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. VCC = 12V, BAT = 4.8V, GND = PGND = 0V, unless otherwise noted.elecTrical characTerisTicsSYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS

VCC Supply

VCC Input Voltage Range l 4.5 34 V

ISHDN Shutdown Quiescent Current (Note 5) VCC = BAT = 4.8V 5 10 µA

IQ Quiescent Current Waiting to Charge (Pause) l 3 5 mA

ICC Operating Current Fast Charge State, No Gate Load l 5 9 mA

VUVLO Undervoltage Threshold Voltage VCC Increasing l 3.85 4.2 4.45 V

VUV(HYST) Undervoltage Hysteresis Voltage 170 mV

VSHDNI Shutdown Threshold Voltage DCIN – VCC, DCIN Increasing l 5 30 60 mV

VSHDND Shutdown Threshold Voltage DCIN – VCC, DCIN Decreasing l –60 –25 –5 mV

VCE Charge Enable Threshold Voltage VCC – BAT, VCC Increasing l 400 510 600 mV

INTVDD Regulator

VDD Output Voltage No Load l 4.5 5 5.5 V

IDD Short-Circuit Current (Note 6) INTVDD = 0V l –100 –50 –10 mA

INTVDD(MIN) Output Voltage VCC = 4.5V, IDD = –10mA l 3.85 V

FE PACKAGE20-LEAD PLASTIC TSSOP

1

2

3

4

5

6

7

8

9

10

TOP VIEW

20

19

18

17

16

15

14

13

12

11

DCIN

FAULT

CHRG

CHEM

GND

VRT

VTEMP

VCELL

VCDIV

TIMER

INFET

READY

VCC

TGATE

PGND

BGATE

INTVDD

TOC

BAT

SENSE

21

TJMAX=125°C,θJA=38°C/W

EXPOSEDPAD(PIN21)ISGND,MUSTBESOLDEREDTOPCBTOOBTAINSPECIFIEDTHERMALRESISTANCE

orDer inForMaTionLEADFREEFINISH TAPEANDREEL PARTMARKING PACKAGEDESCRIPTION TEMPERATURERANGE

LTC4011CFE#PBF LTC4011CFE#TRPBF LTC4011CFE 20-LeadPlasticTSSOP 0°Cto85°C

LEADBASEDFINISH TAPEANDREEL PARTMARKING PACKAGEDESCRIPTION TEMPERATURERANGE

LTC4011CFE LTC4011CFE#TR LTC4011CFE 20-LeadPlasticTSSOP 0°Cto85°C

ConsultLTCMarketingforpartsspecifiedwithwideroperatingtemperatureranges.Formoreinformationonleadfreepartmarking,goto:http://www.linear.com/leadfree/Formoreinformationontapeandreelspecifications,goto:http://www.linear.com/tapeandreel/

LTC4011

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elecTrical characTerisTicsSYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS

Thermistor Termination

VRT Output Voltage RL = 10k

l

3.0753

3.3 3.5253.6

VV

IRT Short-Circuit Current VRT = 0V l –9 –1 mA

PWM Current Source

VFS BAT – SENSE Full-Scale Regulation Voltage (Fast Charge)

0.3V < BAT < VCC – 0.3V (Note 5) BAT = 4.8V

l

9595

100100

105105

mVmV

VPC BAT – SENSE Precharge Regulation Voltage 0.3V < BAT < VCC – 0.3V (Note 5) BAT = 4.8V

l

1616

2020

2424

mVmV

VTC BAT – SENSE Top-Off Charge Regulation Voltage

0.3V < BAT < VCC – 0.3V (Note 5) BAT = 4.8V

l

6.56.5

1010

13.513.5

mVmV

∆VLI BAT – SENSE Line Regulation 5.5V < VCC < 25V, Fast Charge ±0.3 mV

IBAT BAT Input Bias Current 0.3V < BAT < VCC – 0.1V –2 2 mA

ISENSE SENSE Input Bias Current SENSE = BAT 50 150 µA

IOFF Input Bias Current SENSE or BAT, VCELL = 0V l –1 0 1 µA

fTYP Typical Switching Frequency l 460 550 640 kHz

fMIN Minimum Switching Frequency l 20 30 kHz

DCMAX Maximum Duty Cycle 98 99 %

VOL(TG) TGATE Output Voltage Low (VCC – TGATE, Note 7)

VCC > 9V, No Load VCC < 7V, No Load

l

l

5VCC–0.5

5.6VCC

8.75 VV

VOH(TG) TGATE Output Voltage High VCC – TGATE, No Load l 0 50 mV

tR(TG) TGATE Rise Time CLOAD = 3nF, 10% to 90% 35 100 ns

tF(TG) TGATE Fall Time CLOAD = 3nF, 10% to 90% 45 100 ns

VOL(BG) BGATE Output Voltage Low No Load l 0 50 mV

VOH(BG) BGATE Output Voltage High No Load l INTVDD–0.075 INTVDD V

tR(BG) BGATE Rise Time CLOAD = 1.6nF, 10% to 90% 35 80 ns

tF(BG) BGATE Fall Time CLOAD = 1.6nF, 10% to 90% 15 80 ns

ADC Inputs

ILEAK Analog Channel Leakage 0V < VCELL < 2V, 550mV < VTEMP < 2V ±100 nA

Charger Thresholds

VBP Battery Present Threshold Voltage l 320 350 370 mV

VBOV Battery Overvoltage l 1.815 1.95 2.085 V

VMFC Minimum Fast Charge Voltage l 850 900 950 mV

VFCBF Fast Charge Battery Fault Voltage l 1.17 1.22 1.27 V

∆VTERM –∆V Termination CHEM OPEN (NiCd) CHEM = 0V (NiMH)

l

l

166

2010

2514

mVmV

VAR Automatic Recharge Voltage VCELL Decreasing l 1.260 1.325 1.390 V

∆TTERM ∆TTermination(Note8) CHEM = 3.3V (NiCd) CHEM = 0V (NiMH)

l

l

1.30.5

21

2.71.5

°C/min°C/min

TMIN Minimum Charging Temperature (Note 8) VTEMP Increasing l 0 5 9 °C

TMAXI Maximum Charge Initiation Temperature (Note 8)

VTEMP Decreasing, Not Charging l 41.5 45 47 °C

The l indicates specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. VCC = 12V, BAT = 4.8V, GND = PGND = 0V, unless otherwise noted.

LTC4011

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SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS

TMAXC Maximum Fast Charge Temperature (Note 8)

VTEMP Decreasing, Fast Charge l 57 60 63 °C

VTEMP(D) VTEMP Disable Threshold Voltage l 2.8 3.3 V

VTEMP(P) Pause Threshold Voltage l 130 280 mV

Charger Timing

∆tTIMER Internal Time Base Error l –10 10 %

∆tMAX Programmable Timer Error RTIMER = 49.9k l –20 20 %

PowerPath Control

VFR INFET Forward Regulation Voltage DCIN – VCC l 15 55 100 mV

VOL(INFET) Output Voltage Low VCC – INFET, No Load l 3.75 5.2 7 V

VOH(INFET) Output Voltage High VCC – INFET, No Load l 0 50 mV

tOFF(INFET) INFET OFF Delay Time CLOAD = 10nF, INFET to 50% 3 15 µs

Status and Chemistry Select

VOL Output Voltage Low (ILOAD = 10mA) VCDIV All Other Status Outputs

l

l

435300

700600

mVmV

ILKG Output Leakage Current All Status Outputs Inactive, VOUT = VCC l –10 10 µA

IIH(VCDIV) Input Current High VCDIV = VBAT (Shutdown) l –1 1 µA

VIL Input Voltage Low CHEM (NiMH) l 900 mV

VIH Input Voltage High CHEM (NiCd) l 2.85 V

IIL Input Current Low CHEM = GND l –20 –5 µA

IIH Input Current High CHEM = 3.3V l –20 20 µA

elecTrical characTerisTics The l indicates specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. VCC = 12V, BAT = 4.8V, GND = PGND = 0V, unless otherwise noted.

Note1:StressesbeyondthoselistedunderAbsoluteMaximumRatingsmaycausepermanentdamagetothedevice.ExposuretoanyAbsoluteMaximumRatingconditionforextendedperiodsmayaffectdevicereliabilityandlifetime.Note2:TheLTC4011Cisguaranteedtomeetperformancespecificationsfrom0°Cto70°C.Specificationsoverthe0°Cto85°Coperatingtemperaturerangeareassuredbydesign,characterizationandcorrelationwithstatisticalprocesscontrols.Note3:OperatingjunctiontemperatureTJ(in°C)iscalculatedfromtheambienttemperatureTAandthetotalcontinuouspackagepowerdissipationPD(inwatts)bytheformula: TJ=TA+θJA•PDRefertotheApplicationsInformationsectionfordetails.ThisICincludesovertemperatureprotectionthatisintendedtoprotectthedeviceduringmomentaryoverloadconditions.Junctiontemperaturewillexceed125°C

whenovertemperatureprotectionisactive.Continuousoperationabovethespecifiedmaximumoperatingjunctiontemperaturemayresultindevicedegradationorfailure.Note4:Allcurrentintodevicepinsispositive.Allcurrentoutofdevicepinsisnegative.AllvoltagesarereferencedtoGND,unlessotherwisespecified.Note5:Theselimitsareguaranteedbycorrelationtowaferlevelmeasurements.Note6:Outputcurrentmaybelimitedbyinternalpowerdissipation.RefertotheApplicationsInformationsectionfordetails.Note7:EitherTGATEVOHmayapplyfor7.5V<VCC<9V.Note8:TheselimitsapplyspecificallytothethermistornetworkshowninFigure5intheApplicationsInformationsectionwiththevaluesspecifiedfora10kNTC(βof3750).LimitsarethenguaranteedbyspecificVTEMPvoltagemeasurementsduringtest.

LTC4011

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Typical perForMance characTerisTicsNiCdChargeCycleat1C NiCdChargeCycleat2C

NiMHChargeCycleat0.5CBatteryPresentThresholdVoltage(perCell)

MinimumFastChargeThresholdVoltage(perCell)

AutomaticRechargeThresholdVoltage(perCell)

BatteryOvervoltageThresholdVoltage(perCell) –∆VTerminationVoltage(perCell)

LTC4011

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Typical perForMance characTerisTicsProgrammableTimerAccuracy ChargeCurrentAccuracy

ChargerEfficiencyatIOUT=2A ChargerSoft-StartFastChargeCurrentLineRegulation

FastChargeCurrentOutputRegulation

PWMSwitchingFrequency

INFETForwardRegulationVoltage INFETOFFDelayTime

LTC4011

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Typical perForMance characTerisTicsPowerPathSwitching

100µs/DIV

CURR

ENT

(µA)

CURR

ENT

(µA)

ShutdownQuiescentCurrent PWMInputBiasCurrent(OFF)

UndervoltageLockoutThresholdVoltage

ShutdownThresholdVoltage(DCIN–VCC)

ChargeEnableThresholdVoltage(VCC–BAT)

ThermistorDisableThresholdVoltage PauseThresholdVoltage

LTC4011

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pin FuncTionsDCIN(Pin1):DCPowerSenseInput.TheLTC4011sensesvoltage on this pin to determine when an external DCpowersource ispresent.This inputshouldbe isolatedfromVCCbyablockingdiodeorPowerPathFET.RefertotheApplicationsInformationsectionforcompletedetails.OperatingvoltagerangeisGNDto34V.

FAULT (Pin 2): Active-Low Fault Indicator Output. TheLTC4011indicatesvariousbatteryandinternalfaultcondi-tionsbyconnectingthispintoGND.RefertotheOperationandApplicationsInformationsectionsforfurtherdetails.ThisoutputiscapableofdrivinganLEDandshouldbeleftfloatingifnotused.FAULTisanopen-drainoutputtoGNDwithanoperatingvoltagerangeofGNDtoVCC.

CHRG(Pin3):Active-LowChargeIndicatorOutput.TheLTC4011indicatesitisprovidingchargetothebatterybyconnectingthispintoGND.RefertotheOperationandApplicationsInformationsectionsforfurtherdetails.Thisoutput iscapableofdrivinganLEDandshouldbe leftfloatingifnotused.CHRGisanopen-drainoutputtoGNDwithanoperatingvoltagerangeofGNDtoVCC.

CHEM(Pin4):BatteryChemistrySelection Input.ThispinshouldbewiredtoGNDtoselectNiMHfastchargeterminationparameters.Ifavoltagegreaterthan2.85Visappliedtothispin,oritisleftfloating,NiCdparametersareused.RefertotheApplicationsInformationsectionforfurtherdetails.OperatingvoltagerangeisGNDto3.3V.

GND (Pin5):Ground.Thispinprovidesa single-pointgroundfor internalreferencesandothercriticalanalogcircuits.

VRT(Pin6):ThermistorNetworkTerminationOutput.TheLTC4011provides3.3VonthispintodriveanexternalthermistornetworkconnectedbetweenVRT,VTEMPandGND.Additionalpowershouldnotbedrawnfromthispinbythehostapplication.

VTEMP(Pin7):BatteryTemperatureInput.AnexternalthermistornetworkmaybeconnectedtoVTEMPtoprovidetemperature-based chargequalification and additionalfastchargeterminationcontrol.ChargingmayalsobepausedbyconnectingtheVTEMPpintoGND.RefertotheOperationandApplicationsInformationsectionsforcompletedetailsonexternal thermistornetworks andchargecontrol.IfthispinisnotuseditshouldbewiredtoVRT.OperatingvoltagerangeisGNDto3.3V.

VCELL(Pin8):AverageSingle-CellVoltageInput.Anexter-nalvoltagedividerbetweenBATandVCDIVisattachedtothispintomonitortheaveragesingle-cellvoltageofthebatterypack.TheLTC4011usesthisinformationtoprotectagainstcatastrophicbatteryovervoltageandtocontrolthechargingstate.RefertotheApplicationsInformationsectionforfurtherdetailsontheexternaldividernetwork.OperatingvoltagerangeisGNDtoBAT.

INTVDDVoltage INTVDDShort-CircuitCurrent

Typical perForMance characTerisTics

LTC4011

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pin FuncTionsVCDIV(Pin9):AverageCellVoltageResistorDividerTermi-nation.TheLTC4011connectsthispintoGNDprovidedthechargerisnotinshutdown.VCDIVisanopen-drainoutputtoGNDwithanoperatingvoltagerangeofGNDtoBAT.

TIMER(Pin10):ChargeTimerInput.AresistorconnectedbetweenTIMERandGNDprogramschargecycletiminglimits.RefertotheApplicationsInformationsectionforcompletedetails.OperatingvoltagerangeisGNDto1V.

SENSE(Pin11):ChargeCurrentSenseInput.AnexternalresistorbetweenthisinputandBATisusedtoprogramcharge current. Refer to the Applications Informationsection for complete details on programming chargecurrent.Operatingvoltagerangesfrom(BAT–50mV)to(BAT+200mV).

BAT(Pin12):BatteryPackConnection.TheLTC4011usesthevoltageonthispintocontrolcurrentsourcedfromVCCtothebatteryduringcharging.AllowableoperatingvoltagerangeisGNDtoVCC.

TOC(Pin13):Active-LowTop-OffChargeIndicatorOut-put.TheLTC4011indicatesthetop-offchargestateforNiMHbatteriesbyconnectingthispintoGND.RefertotheOperationandApplicationsInformationsectionsforfurtherdetails.ThisoutputiscapableofdrivinganLEDandshouldbeleftfloatingifnotused.TOCisanopen-drainoutputtoGNDwithanoperatingvoltagerangeofGNDtoVCC.

INTVDD(Pin14):Internal5VRegulatorOutput.Thispinprovidesameansofbypassingtheinternal5VregulatorusedtopowertheBGATEoutputdriver.Typically,powershould not be drawn from this pin by the applicationcircuit.Refer totheApplicationInformationsectionforadditionaldetails.

BGATE(Pin15):ExternalSynchronousN-channelMOSFETGateControlOutput.ThisoutputprovidesgatedrivetoanoptionalexternalNMOSpowertransistorswitchusedforsynchronousrectificationtoincreaseefficiencyinthestep-downDC/DCconverter.OperatingvoltageisGNDtoINTVDD.BGATEshouldbeleftfloatingifnotused.

PGND(Pin16):PowerGround.ThispinprovidesareturnforswitchingcurrentsgeneratedbyinternalLTC4011cir-cuits.Externally,PGNDandGNDshouldbewiredtogetherusing a very low impedance connection. Refer to PCBLayout Considerations in the Applications Informationsectionforadditionalgroundingdetails.

TGATE(Pin17):ExternalP-channelMOSFETGateControlOutput.ThisoutputprovidesgatedrivetoanexternalPMOSpowertransistorswitchusedintheDC/DCconverter.Op-eratingvoltagerangevariesasafunctionofVCC.RefertotheElectricalCharacteristicstableforspecificvoltages.

VCC(Pin18):PowerInput.ExternalPowerPathcontrolcircuitsnormallyconnecteithertheDCinputpowersup-plyor thebattery to thispin.Refer to theApplicationsInformationsectionforfurtherdetails.SuggestedappliedvoltagerangeisGNDto34V.

READY (Pin 19): Active-Low Ready-to-Charge Output.TheLTC4011connectsthispintoGNDifproperoperatingvoltagesforchargingarepresent.RefertotheOperationsectionforcompletedetailsonchargequalification.Thisoutput iscapableofdrivinganLEDandshouldbe leftfloating ifnotused.READY isanopen-drainoutput toGNDwithanoperatingvoltagerangeofGNDtoVCC.

INFET(Pin20):PowerPathControlOutput.Forverylowdropoutapplications, thisoutputmaybeused todrivethe gate of an input PMOS pass transistor connectedbetweentheDCinput(DCIN)andtherawsystemsupplyrail(VCC).INFETisinternallyclampedabout6VbelowVCC.MaximumoperatingvoltageisVCC.INFETshouldbeleftfloatingifnotused.

Exposed Pad (Pin 21): This pin provides enhancedthermalpropertiesfortheTSSOP.ItmustbesolderedtothePCBcoppergroundtoobtainoptimumthermalperformance.

LTC4011

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block DiagraM

7

8

13

14

CHARGERSTATE

CONTROLLOGIC

THERMISTORINTERFACE

A/DCONVERTER

BATTERYDETECTOR

VOLTAGEREGULATOR

UVLO ANDSHUTDOWN

PWM

FET DIODE

CHARGETIMER

VOLTAGEREFERENCE

INTERNALVOLTAGE

REGULATOR

VTEMP

6VRT

4CHEM

3CHRG

2FAULT

1

12

11

15

16

17

DCIN

5 GND

VCELL

10TIMER

9VCDIV

TOC

INTVDD

4011 BD

SENSE

BAT

PGND

19READY

INFET

VCC

BGATE

TGATE

20

18

LTC4011

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operaTion

Figure1.LTC4011StateDiagram

LTC4011

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operaTionShutdownState

TheLTC4011remainsinmicropowershutdownuntilDCIN(Pin1)isdrivenaboveVCC(Pin18).InshutdownallstatusandPWMoutputsandinternallygeneratedterminationsorsupplyvoltagesareinactive.CurrentconsumptionfromVCCandBATisreducedtoaverylowlevel.

ChargeQualificationState

Once DCIN is greater than VCC, the LTC4011 exitsmicropowershutdown,enablesitsowninternalsupplies,providesVRTvoltagefortemperaturesensing,andswitchesVCDIVtoGNDtoallowmeasurementoftheaveragesingle-cellvoltage.TheICalsoverifiesthatVCCisatorabove4.2V,VCCis510mVaboveBATandVCELLisbetween350mVand1.95V.IfVCELLisbelow350mV,nochargingwilloccur,andifVCELLisabove1.95V,thefaultstateisentered,whichisdescribedinmoredetailbelow.Onceadequatevoltageconditionsexistforcharging,READYisasserted.

IfthevoltagebetweenVTEMPandGNDisbelow200mV,theLTC4011ispaused.IfVTEMPisabove200mVbutbelow2.85V,theLTC4011verifiesthatthesensedtemperatureisbetween5°Cand45°C.Ifthesetemperaturelimitsarenotmetorifitsowndietemperatureistoohigh,theLTC4011willindicateafaultandnotallowchargingtobegin.IfVTEMPisgreaterthan2.85V,batterytemperaturerelatedchargequalification,monitoringandterminationaredisabled.

Oncechargingisfullyqualified,prechargebegins(unlesstheLTC4011 ispaused). In thatcase, theVTEMPpin ismonitoredforfurthercontrol.ThechargestatusindicatorsandPWMoutputsremaininactiveuntilchargingbegins.

ChargeMonitoring

TheLTC4011continuestomonitorimportantvoltageandtemperatureparametersduringallchargingstates.IftheDCinputisremoved,chargingstopsandtheshutdownstateisentered.IfVCCdropsbelow4.25VorVCELLdropsbelow350mV,chargingstopsandtheLTC4011returnstothechargequalificationstate.IfVCELLexceeds1.95V,chargingstopsandtheICentersthefaultstate.Ifanexternalthermistorindicatessensedtemperatureisbeyondarangeof5°Cto60°C,ortheinternaldietemperatureexceedsaninternalthermallimit,chargingissuspended,thechargetimerispausedandtheLTC4011indicatesafaultcondition.

Normalchargingresumesfromthepreviousstatewhenthesensedtemperaturereturnstoasatisfactoryrange.Inaddition,otherbatteryfaultsaredetectedduringspecificchargingstatesasdescribedbelow.

PrechargeState

IftheinitialvoltageonVCELLisbelow900mV,theLTC4011enterstheprechargestateandenablesthePWMcurrentsourcetotricklechargeusingone-fifththeprogrammedchargecurrent.TheCHRGstatusoutputisactiveduringprecharge. The precharge state duration is limited totMAX/12minutes,wheretMAXisthemaximumfastchargeperiodprogrammedwiththeTIMERpin.IfsufficientVCELLvoltagecannotbedevelopedinthislengthoftime,thefaultstateisentered,otherwisefastchargebegins.

FastChargeState

Ifadequateaveragesingle-cellvoltageexists,theLTC4011entersthefastchargestateandbeginschargingattheprogrammedcurrent set by the external current senseresistor connected between the SENSE and BAT pins.TheCHRGstatusoutputisactiveduringfastcharge.IfVCELLisinitiallyabove1.325V,voltage-basedterminationprocessingbeginsimmediately.Otherwise–∆Vterminationisdisabledforastabilizationperiodof tMAX/12. In thatcase,theLTC4011makesanotherfaultcheckattMAX/12,requiringtheaveragecellvoltagetobeabove1.22V.Thisensures the battery pack is accepting a fast charge. IfVCELLisnotabovethisvoltagethreshold,thefaultstateisentered.FastchargestatedurationislimitedtotMAXandthefaultstateisenteredifthislimitisexceeded.

ChargeTermination

FastchargeterminationparametersaredependentuponthebatterychemistryselectedwiththeCHEMpin.Voltage-basedtermination(–∆V)isalwaysactiveaftertheinitialvoltagestabilizationperiod.Ifanexternalthermistornetworkispresent,chemistry-specificlimitsfor∆T/∆t(rateoftem-peraturerise)arealsousedintheterminationalgorithm.Temperature-basedtermination,ifenabled,becomesactiveassoonas the fast chargestate isentered.SuccessfulchargeterminationrequiresachargeratebetweenC/2and2C.Lowerratesmaynotproducethebatteryvoltageandtemperatureprofilerequiredforchargetermination.

(RefertoFigure1)

LTC4011

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operaTionTop-OffChargeState

IfNiMHfastchargeterminationoccursbecausethe∆T/∆tlimitisexceededafteraninitialperiodoftMAX/12hasexpired,theLTC4011entersthetop-offchargestate.Top-offchargeisimplementedbysourcingone-tenththeprogrammedchargecurrentfortMAX/3minutestoensurethat100%chargehasbeendeliveredtothebattery.TheCHRGandTOCstatusoutputsareactiveduringthetop-offstate.IfNiCdcellshavebeenselectedwiththeCHEMpin,theLTC4011neverentersthetop-offstate.

AutomaticRechargeState

Oncechargingiscomplete,theautomaticrechargestateisentered toaddress theself-dischargecharacteristicsofnickelchemistrycells.Thechargestatusoutputsareinactive during automatic recharge, but VCDIV remainsswitchedtoGNDtomonitortheaveragecellvoltage.IftheVCELLvoltagedropsbelow1.325Vwithoutfallingbelow350mV,thechargetimerisresetandanewfastchargecycleisinitiated.

The internal terminationalgorithmsoftheLTC4011areadjustedwhenafastchargecycleisinitiatedfromauto-maticrecharge,becausethebatteryshouldbealmostfullycharged.Voltage-basedterminationisenabledimmediatelyandtheNiMH∆T/∆tlimitisfixedatabatterytemperatureriseof1°C/minute.

FaultState

Asdiscussedpreviously,theLTC4011entersthefaultstatebasedondetectionofinvalidbatteryvoltagesduringvari-ouschargingphases.TheICalsomonitorstheregulationofthePWMcontrolloopandwillenterthefaultstateifthisisnotwithinacceptablelimits.Onceinthefaultstate,thebatterymustberemovedorDCinputpowermustbecycled inorder to initiate further charging. In the faultstate, theFAULT output is active, theREADY output isinactive,chargingstopsandthechargeindicatoroutputsareinactive.TheVCDIVoutputremainsconnectedtoGNDtoallowdetectionofbatteryremoval.

NotethattheLTC4011alsousestheFAULToutputtoindi-catethatchargingissuspendedduetoinvalidbatteryorinternaldietemperatures.However,theICdoesnotenterthefaultstateinthesecasesandnormaloperationwill

resumewhenalltemperaturesreturntoacceptablelevels.RefertotheStatusOutputssectionformoredetail.

InsertionandRemovalofBatteries

TheLTC4011automaticallysensestheinsertionorremovalofabatterybymonitoringtheVCELLpinvoltage.Shouldthisvoltagefallbelow350mV,theICconsidersthebat-terytobeabsent.RemovingandtheninsertingabatterycausestheLTC4011toinitiateacompletelynewchargecyclebeginningwithchargequalification.

ExternalPauseControl

Afterchargingisinitiated,theVTEMPpinmaybeusedtopauseoperationatanytime.WhenthevoltagebetweenVTEMP and GND drops below 200mV, the charge timerpauses,fastchargeterminationalgorithmsareinhibitedandthePWMoutputsaredisabled.ThestatusandVCDIVoutputsallremainactive.Normalfunctionisfullyrestoredfromthepreviousstatewhenpauseends.

StatusOutputs

TheLTC4011open-drainstatusoutputsprovidevaluableinformation about the IC’s operating state and can beused foravarietyofpurposes inapplications.Table1summarizesthestateofthefourstatusoutputsandtheVCDIVpinasafunctionofLTC4011operation.Thestatusoutputscandirectlydrivecurrent-limitedLEDsterminatedtotheDCinput.TheVCDIVcolumninTable1isstrictlyinformational.VCDIVshouldonlybeusedfortheVCELLresistordivider,aspreviouslydiscussed.

Table1.LTC4011StatusPinsREADY FAULT CHRG TOC VCDIV CHARGERSTATE

Off Off Off Off Off Off

On Off Off Off On ReadytoCharge(VTEMPHeldLow)

orAutomaticRecharge

On Off On Off On PrechargeorFastCharge(MaybePaused)

On Off On On On NiMHTop-OffCharge(MaybePaused)

On On OnorOff OnorOff On TemperatureLimitsExceeded

Off On Off Off On FaultState(Latched)

LTC4011

��4011fb

operaTion

12

–

+

CC

EAITH

IPROG

R3

QPWM CLOCKS

R

R4

R1

BAT

11SENSE

RSENSE

15BGATE

17TGATE

LTC4011VCC

P

N

R2

4011 F02

Figure2.LTC4011PWMControlLoop

PWMCurrentSourceController

AnintegralpartoftheLTC4011isthePWMcurrentsourcecontroller. The chargeruses a synchronous step-downarchitecturetoproducehighefficiencyandlimitedthermaldissipation.Thenominaloperatingfrequencyof550kHzallowsuseofasmallerexternalfiltercomponents.TheTGATEandBGATEoutputshaveinternallyclampedvolt-ageswings.Theysourcepeakcurrentstailoredtosmallersurface-mountpowerFETslikelytoappearinapplicationsprovidinganaveragechargecurrentof3Aorless.Duringthevariouschargingstates,theLTC4011usesthePWMcontrollertoregulateanaveragevoltagebetweenSENSEandBATthatrangesfrom10mVto100mV.

AconceptualdiagramoftheLTC4011PWMcontrolloopisshowninFigure2.

The voltage across the external current programmingresistorRSENSEisaveragedbyintegratingerroramplifierEA.AninternalprogrammingcurrentisalsopulledfrominputresistorR1.TheIPROG•R1productestablishesthedesiredaveragevoltagedropacrossRSENSE,andhence,theaveragecurrent throughRSENSE.The ITHoutputoftheerroramplifierisascaledcontrolcurrentfortheinput

ofthePWMcomparatorCC.TheITH•R3productsetsapeakcurrentthresholdforCCsuchthatthedesiredaver-agecurrent throughRSENSE ismaintained.ThecurrentcomparatoroutputdoesthisbyswitchingthestateoftheSRlatchattheappropriatetime.

Atthebeginningofeachoscillatorcycle,thePWMclocksetstheSRlatchandtheexternalP-channelMOSFETisswitchedon(N-channelMOSFETswitchedoff)torefreshthecurrentcarriedbytheexternalinductor.Theinductorcurrent and voltage drop across RSENSE begin to riselinearly. During normal operation, the PFET is turnedoff(NFETon)duringthecyclebyCCwhenthevoltagedifferenceacrossRSENSEreachesthepeakvaluesetbytheoutputofEA.TheinductorcurrentthenrampsdownlinearlyuntilthenextrisingPWMclockedge.Thisclosestheloopandmaintainsthedesiredaveragechargecurrentintheexternalinductor.

LowDropoutCharging

Afterchargingisinitiated,theLTC4011doesnotrequirethatVCCremainatleast500mVaboveBATbecausesitu-ationsexistwherelowdropoutchargingmightoccur.Inoneinstance,parasiticseriesresistancemaylimitPWMheadroom (between VCC and BAT) as 100% charge isreached.AsecondcasecanarisewhentheDCadapterselectedbytheenduserisnotcapableofdeliveringthecurrentprogrammedbyRSENSE,causingtheoutputvolt-ageoftheadaptertocollapse.Whileinlowdropout,theLTC4011PWMrunsnear100%dutycyclewithafrequencythatmaynotbeconstantandcanbelessthan550kHz.Thechargecurrentwilldropbelowtheprogrammedvaluetoavoidgeneratingaudiblenoise,sotheactualchargedelivered to the battery may depend primarily on theLTC4011chargetimer.

InternalDieTemperature

TheLTC4011providesinternalovertemperaturedetectiontoprotectagainstelectricaloverstress,primarilyattheFETdriveroutputs.Ifthedietemperaturerisesabovethisthermallimit,theLTC4011stopsswitchingandindicatesafaultaspreviouslydiscussed.

LTC4011

��4011fb

applicaTions inForMaTionExternalDCSource

TheexternalDCpowersourceshouldbeconnectedtothechargingsystemandtheVCCpinthrougheitherapowerdiodeorP-channelMOSFET.Thispreventscatastrophicsystemdamageintheeventofaninputshorttogroundorreverse-voltagepolarityattheDCinput.TheLTC4011auto-maticallysenseswhenthisinputispresent.Theopen-circuitvoltageoftheDCsourceshouldbebetween4.5Vand34V,dependingonthenumberofcellsbeingcharged.Inordertoavoidlowdropoutoperation,ensure100%capacityatchargetermination,andallowreliabledetectionofbatteryinsertion,removalorovervoltage,thefollowingequationcanbeusedtodeterminetheminimumfull-loadvoltagethatshouldbeprovidedbytheexternalDCpowersource.

DCIN(MIN)=(n•2V)+0.3V

wherenisthenumberofseriescellsinthebatterypack.

The LTC4011 will properly charge over a wide rangeof DCIN and BAT voltage combinations. Operating theLTC4011inlowdropoutorwithDCINmuchgreaterthanBATwillforcethePWMfrequencytobemuchlessthan550kHz.TheLTC4011disableschargingandsetsafaultifalargeDCINtoBATdifferentialwouldcausegenerationofaudiblenoise.

PowerPathControl

ProperPowerPathcontrolisanimportantconsiderationwhenfastchargingnickelcells.Thiscontrolensuresthatthesystemloadremainspoweredatall times,butthatnormalsystemoperationandassociatedloadtransientsdonotadverselyaffectfastchargetermination.Forhighefficiencyandlowdropoutapplications,theLTC4011canprovidegatedrivefromtheINFETpindirectlytoaninputP-channelMOSFET.

Thebatteryshouldalsobeconnectedtotherawsystemsupply by a switch that selects the battery for systempoweronlyifanexternalDCsourceisnotpresent.Again,forapplicationsrequiringhigherefficiency,aP-channelMOSFETwithitsgatedrivenfromtheDCinputcanbeusedtoperformthisswitchingfunction(seeFigure8).GatevoltageclampingmaybenecessaryonanexternalPMOStransistorusedinthismannerathigherinputvoltages.Alternatively,adiodecanbeusedinplaceofthisFET.

BatteryChemistrySelection

ThedesiredbatterychemistryisselectedbyprogrammingtheCHEMpintothepropervoltage.IfitiswiredtoGND,a set of parameters specific to charging NiMH cells isselected.WhenCHEMisleftfloatingorconnectedtoVRT,chargingisoptimizedforNiCdcells.ThevariouschargingparametersaredetailedinTable2.

ProgrammingChargeCurrent

Charge current is programmed using the followingequation:

R

mVISENSEPROG

= 100

RSENSE is an external resistor connected between theSENSEandBATpins.A1%resistorwithalowtemperaturecoefficientandsufficientpowerdissipationcapabilitytoavoidself-heatingeffectsisrecommended.ChargerateshouldbebetweenapproximatelyC/2and2C.

InductorValueSelection

Formanyapplications,10µHrepresentsanoptimumvaluefortheinductorthePWMusestogeneratechargecurrent.For applicationswith IPROG of 1.5A or greater runningfromanexternalDCsourceof15Vorless,valuesbetween5µHand7.5µHcanoftenbeselected.Forwideroperatingconditionsthefollowingequationcanbeusedasaguideforselectingtheminimuminductorvalue.

L>6.5•10–6•VDCIN•RSENSE,L≥4.7µH

Actualpartselectionshouldaccountforbothmanufacturingtoleranceandtemperaturecoefficienttoensurethismini-mum.Agoodinitialselectioncanbemadebymultiplyingthecalculatedminimumby1.4androundingupordowntotheneareststandardinductancevalue.

Ultimately,thereisnosubstituteforbenchevaluationoftheselectedinductorinthetargetapplication,whichcanalsobeaffectedbyotherenvironmentalfactorssuchasambient operating temperature. Using inductor valueslowerthanrecommendedbytheequationshownabovecanresultinafaultconditionatthestartofprechargeortop-offcharge.

LTC4011

��4011fb

ProgrammingMaximumChargeTimes

ConnectingtheappropriateresistorbetweentheTIMERpinandGNDprogramsthemaximumdurationofvariouschargingstates.Tosomedegree,thevalueshouldreflecthowcloselytheprogrammedchargecurrentmatchesthe1Crateoftargetedbatterypacks.Themaximumfastchargeperiodisdeterminedbythefollowingequation:

SometypicaltimingvaluesaredetailedinTable3.RTIMERshouldnotbelessthan15k.TheactualtimelimitsusedbytheLTC4011havearesolutionofapproximately±30secondsinadditiontothetolerancesgiventheElectricalCharacteristicstable.Ifthetimerendswithoutavalid–∆Vor∆T/∆tchargetermination,thechargerentersthefaultstate.Themaximumtimeperiodisapproximately4.3hours.

CellVoltageNetworkDesign

Anexternal resistornetwork is required toprovide theaveragesingle-cellvoltagetotheVCELLpinoftheLTC4011.

ThepropercircuitformulticellpacksisshowninFigure3.TheratioofR2toR1shouldbeafactorof(n–1),wherenisthenumberofseriescellsinthebatterypack.ThevalueofR1shouldbebetween1kand100k.ThisrangelimitsthesensingerrorcausedbyVCELLleakagecurrentandpreventstheONresistanceoftheinternalNFETbe-tweenVCDIVandGNDfromcausingasignificanterrorintheVCELLvoltage.Theexternalresistornetworkisalsoused todetectbattery insertionandremoval.ThefilterformedbyC1andtheparallelcombinationofR1andR2

12

9

BAT

LTC4011 R2+

FOR TWO ORMORE SERIES CELLS

R1 C1

R2 = R1(n – 1)

4011 F03

VCDIV

GND

8

5

VCELL

Figure3.MulitpleCellVoltageDivider

applicaTions inForMaTionTable2.LTC4011ChargingParameters

STATECHEM

PINBAT

CHEMISTRY TIMER TMIN TMAX ICHRG TERMINATIONCONDITIONPC Both tMAX/12 5°C 45°C IPROG/5 TimerExpires

FC Open NiCd tMAX 5°C 60°C IPROG –20mVperCellor2°C/Minute

GND NiMH tMAX 5°C 60°C IPROG 1.5°C/MinuteforFirsttMAX/12MinutesifInitialVCELL<1.325V

–10mVperCellor1°C/MinuteAftertMAX/12MinutesorifInitialVCELL>1.325V

TOC GND NiMH tMAX/3 5°C 60°C IPROG/10 TimerExpires

AR Both 5°C 45°C 0 VCELL<1.325V

PC: PrechargeFC: FastCharge(Initial–∆VTerminationHoldOffoftMAX/12MinutesMayApply)TOC: Top-OffCharge(OnlyforNiMH∆T/∆tFCTerminationAfterInitialtMAX/12Period)AR: AutomaticRecharge(TemperatureLimitsApplytoStateTerminationOnly)

Table3.LTC4011TimeLimitProgrammingExamples

RTIMER

TYPICALFASTCHARGERATE

PRECHARGELIMIT(MINUTES)

FASTCHARGEVOLTAGESTABILIZATION

(MINUTES)FASTCHARGELIMIT

(HOURS)

TOP-OFFCHARGE

(MINUTES)24.9k 2C 3.8 3.8 0.75 15

33.2k 1.5C 5 5 1 20

49.9k 1C 7.5 7.5 1.5 30

66.5k 0.75C 10 10 2 40

100k C/2 15 15 3 60

LTC4011

��4011fb

applicaTions inForMaTion

Figure4.Single-CellMonitorNetwork

12

9

BAT

10k 10k

33nF

1 CELL

4011 F04

VCDIV

8VCELL

where:

R0=thermistorresistance(Ω)atT0

T0=thermistorreferencetemperature(°K)

β=exponentialtemperaturecoefficientofresistance

Forthermistorswithβlessthan3750,theequationforR3yieldsanegativenumber.ThisnumbershouldbeusedtocomputeR2,eventhoughR3isreplacedwithashortintheactualapplication.Anadditionalhightemperaturechargequalificationerrorofbetween0°Cand5°Cmayoccurwhenusingthermistorswithβ lowerthan3750.Thermistorswithnominalβlessthan3300shouldbeavoided.

Thefilter formedbyR4andC1 inFigure5 isoptionalbut recommended for rejecting PWM switching noise.Alternatively,R4maybereplacedbyashort,andavaluechosenforC1whichwillprovideadequatefilteringfromtheTheveninimpedanceoftheremainingthermistornet-work.Thefilterpolefrequency,whichshouldbelessthan500Hz,willvarymorewithbatterytemperaturewithoutR4.ExternalcomponentsshouldbechosentomaketheTheveninimpedancefromVTEMPtoGND100kΩorless,includingR4,ifpresent.

DisablingThermistorFunctions

TemperaturesensingisoptionalinLTC4011applications.For lowcost systemswhere temperature sensingmaynotberequired, theVTEMPpinmaysimplybewiredtoVRT todisable temperaturequalificationofallcharging

isrecommendedforrejectingPWMswitchingnoise.ThevalueofC1shouldbechosentoyielda1storderlowpassfrequencyoflessthan500Hz.Inthecaseofasinglecell,theexternalapplicationcircuitshowninFigure4isrec-ommendedtoprovidethenecessarynoisefilteringandmissingbatterydetection.

ThermistorNetworkDesign

The network for proper temperature sensing using athermistorwithanegativetemperaturecoefficient(NTC)isshowninFigure5.R3isonlypresentforthermistorswith an exponential temperature coefficient (β) above3750. For thermistors with β below 3750, replace R3withashort.

Figure5.ExternalNTCThermistorNetwork

6

7

VRT

R1

R2RT

R451k

R3

C110nF

4011 F05

VTEMP

TheLTC4011isdesignedtoworkbestwitha5%10KNTCthermistorwithaβnear3750,suchastheSiemens/EPCOSB57620C103J062.Inthiscase,thevaluesfortheexternalnetworkaregivenby:

R1=9.76k R2=28k R3=0Ω

However,theLTC4011willoperatewithotherNTCtherm-istors having different nominal values or exponentialtemperaturecoefficients.Forthesethermistors,thedesignequationsfortheresistorsintheexternalnetworkare:

LTC4011

��4011fb

applicaTions inForMaTionoperations.However,thispracticeisnotrecommendedforNiMHcellschargedwellaboveorbelowtheir1Crate,becausefastchargeterminationbasedsolelyonvoltageinflectionmaynotbeadequatetoprotectthebatteryfromasevereovercharge.Aresistorbetween10kand20kmaybeusedtoconnectVTEMPtoVRTifthepausefunctionisstilldesired.

INTVDDRegulatorOutput

IfBGATEisleftopen,theINTVDDpinoftheLTC4011canbeusedasanadditionalsourceofregulatedvoltageinthehostsystemanytimeREADYisactive.Switchingloadson INTVDDmay reduce theaccuracyof internalanalogcircuits used to monitor and terminate fast charging.Inaddition,DCcurrentdrawnfromtheINTVDDpincangreatlyincreaseinternalpowerdissipationatelevatedVCCvoltages.Aminimumceramicbypasscapacitorof0.1µFisrecommended.

CalculatingAveragePowerDissipation

TheusershouldensurethatthemaximumratedICjunctiontemperatureisnotexceededunderalloperatingconditions.The thermal resistance of the LTC4011 package (θJA)is38°C/W,provided theexposedmetalpad isproperlysolderedtothePCB.TheactualthermalresistanceintheapplicationwilldependontheamountofPCBcoppertowhichthepackageissoldered.Feedthroughviasdirectlybelow thepackage thatconnect to innercopper layersarehelpfulinloweringthermalresistance.Thefollowingformulamaybeusedtoestimatethemaximumaveragepower dissipation PD (in watts) of the LTC4011 undernormaloperatingconditions.

where:

IDD=AverageexternalINTVDDloadcurrent,ifany

IVRT=LoadcurrentdrawnbytheexternalthermistornetworkfromVRT,ifany

QTGATE=GatechargeofexternalP-channelMOSFETincoulombs

QBGATE=GatechargeofexternalN-channelMOSFET(ifused)incoulombs

VLED=MaximumexternalLEDforwardvoltage

RLED=ExternalLEDcurrent-limitingresistorusedintheapplication

n=NumberofLEDsdrivenbytheLTC4011

SampleApplications

Figures6 through9detailsamplechargerapplicationsofvariouscomplexities.CombinedwiththeTypicalAp-plicationonthefirstpageofthisdatasheet,theseFiguresdemonstrate some of the proper configurations of theLTC4011.MOSFETbodydiodesareshowninthesefiguresstrictlyforreferenceonly.

Figure6showsaminimumapplication,whichmightbeencountered in lowcostNiCd fastchargeapplications.FET-basedPowerPathcontrolallowsformaximuminputvoltage range from the DC adapter. The LTC4011 uses–∆V to terminate the fast charge state, as no externaltemperature information is available. NonsynchronousPWMswitchingisemployedtoreduceexternalcomponentcost.AsingleLEDindicateschargingstatus.

A3ANiMHapplicationofmediumcomplexityisshowninFigure7.PowerPathcontrolthatiscompletelyFET-basedallowsforbothminimuminputvoltageoverheadandmini-mumswitchoverlosswhenoperatingfromthebattery.

P-channelMOSFETQ4functionsasaswitchtoconnectthebatterytothesystemloadwhenevertheDCinputadapterisremoved.IfthemaximumbatteryvoltageislessthanthemaximumratedVGSofQ4,diodeD1andresistorR5are not required. Otherwise choose the Zener voltageofD1tobelessthanthemaximumratedVGSofQ4.R5providesabiascurrentof(VBAT–VZENER)/(R5+20k)forD1whentheinputadapterisremoved.ChooseR5tomakethiscurrent,whichisdrawnfromthebattery,justlargeenoughtodevelopthedesiredVGSacrossD1.

Precharge,fastchargeandtop-offstatesareindicatedbyexternalLEDs.TheVTEMPthermistornetworkallowstheLTC4011toaccuratelyterminatefastchargeunderavarietyofappliedchargerates.UseofasynchronousPWMtopol-ogyimprovesefficiencyandlowerspowerdissipation.

LTC4011

��4011fb

applicaTions inForMaTion

Figure7.3ANiMHChargerwithFullPowerPathControl

Figure6.Minimum1ALTC4011Application

0.1µF

10µF

10µF

10µH

FAULTINFET

CHRG

FROMADAPTER

12V

TOCREADY

0.033µF 0.068µF

20µF

0.1µF

4.7µH

20µF

FAULTCHRGTOCREADY

FROMADAPTER

12V

Afull-featured2ALTC4011applicationisshowninFigure8.FET-basedPowerPathallowsformaximuminputvoltagerangefromtheDCadapter.TheinherentvoltageratingsoftheVCELL,VCDIV,SENSEandBATpinsallowchargingofone tosixteenseriesnickel cells in thisapplication,governedonlybytheVCCoverheadlimitspreviouslydis-cussed.Theapplicationincludesallaveragecellvoltage

andbatterytemperaturesensingcircuitryrequiredfortheLTC4011toutilize its full rangeofchargequalification,safetymonitoringandfastchargeterminationfeatures.LED D1 indicates valid DC input voltage and installedbattery,whileLEDsD2andD3indicatecharging.LEDD4indicatesfaultconditions.ThegroundedCHEMpinselectstheNiMHchargeterminationparameterset.

LTC4011

�04011fb

applicaTions inForMaTion

Figure8.Full-Featured2ALTC4011Application

0.1µF

D1 D2 D3 D4

10µF

6.8µH

10µF

FROMADAPTER

12V

FAULTINFET

CHRGTOCREADY

Figure9.LTC4011withMCUInterface

0.1µF

10µF

22µH

NiMH PACKWITH 10k NTC(1Ahr)

FAULTCHRGTOCREADY

PAUSEFROMMCU

INFET

FROMADAPTER

24V

While theLTC4011 is a complete, standalonesolution,Figure9showsthat itcanalsobe interfaced toahostmicroprocessor.ThehostMCUcancontrolthechargerdirectlywithanopen-drainI/OportconnectedtotheVTEMPpin, if thatport is lowleakageandcantolerateat least

2V.ThechargerstateismonitoredonthefourLTC4011statusoutputs.ChargingofNiMHbatteriesisselectedinthisexample.However,NiCd(CHEM→VRT)parameterscouldbechosenaswell.

LTC4011

��4011fb

applicaTions inForMaTionUnlikealloftheotherapplicationsdiscussedsofar,thebatterycontinuestopowerthesystemduringcharging.TheMCUcouldbepowereddirectlyfromthebatteryorfromanytypeofpostregulatoroperatingfromthebattery.Inthisconfiguration,theLTC4011reliesexpresslyontheabilityofthehostMCUtoknowwhenloadtransientswillbeencountered.TheMCUshould thenpausecharging(andthus–∆Vprocessing)duringthoseeventstoavoidprematurefastchargetermination.IftheMPUcannotreli-ablyperformthisfunction,fullPowerPathcontrolshouldbeimplemented.Inmostapplications,thereshouldnotbeanexternalloadonthebatteryduringcharge.Excessivebatteryloadcurrentvariations,suchasthosegeneratedbyapost-regulatingPWM,cangeneratesufficientvoltagenoisetocausetheLTC4011toprematurelyterminateachargecycleand/orprematurelyrestartafastcharge.Inthiscase,itmaybenecessarytoinhibittheLTC4011aftercharging is completeuntil externalgasgaugecircuitryindicatesthatrechargingisnecessary.ShutdownpowerisappliedtotheLTC4011throughthebodydiodeofQ2inthisapplication.

Waveforms

Samplewaveforms forastandaloneapplicationduringatypicalchargecycleareshowninFigure10.Notethatthesewaveformsarenottoscaleanddonotrepresentthecompleterangeofpossibleactivity.ThefigureissimplyintendedtoallowbetterconceptualunderstandingandtohighlighttherelativebehaviorofcertainsignalsgeneratedbytheLTC4011duringatypicalchargecycle.

Initially, theLTC4011 is in lowpowershutdownas thesystemoperatesfromaheavilydischargedbattery.ADCadapteristhenconnectedsuchthatVCCrisesabove4.25Vandis500mVaboveBAT.TheREADYoutputisassertedwhentheLTC4011completeschargequalification.

WhentheLTC4011determineschargingshouldbegin,itstartsaprechargecyclebecauseVCELLislessthan900mV.As long as the temperature remains within prescribedlimits,theLTC4011charges(TGATEswitching),applyinglimitedcurrenttothebatterywiththePWMinordertobringtheaveragecellvoltageto900mV.

When the precharge state timer expires, the LTC4011begins fastcharge ifVCELL isgreater than900mV.The

PWM,chargetimerandinternalterminationcontrolaresuspendedifpauseisasserted(VTEMP<200mV),butallstatusoutputscontinuetoindicatechargingisinprogress.Thefastchargestatecontinuesuntiltheselectedvoltageortemperatureterminationcriteriaaremet.Figure10sug-geststerminationbasedon∆T/∆t,whichforNiMHwouldbeanincreasegreaterthan1°Cperminute.

BecauseNiMHchargingterminateddueto∆T/∆tandthefastchargecyclehadlastedmorethantMAX/12minutes,theLTC4011begins a top-off chargewith a current ofIPROG/10.Top-offisaninternallytimedchargeoftMAX/3minuteswith theCHRG andTOCoutputscontinuouslyasserted.

Finally,theLTC4011enterstheautomaticrechargestatewhere theCHRGandTOCoutputsaredeasserted.ThePWMisdisabledbutVCDIVremainsassertedtomonitorVCELL.ThechargetimerwillberesetandfastchargingwillresumeifVCELLdropsbelow1.325V.TheLTC4011entersshutdownwhentheDCadapterisremoved,minimizingcurrentdrawfromthebatteryintheabsenceofaninputpowersource.

WhilenotapartofthesamplewaveformsofFigure10,temperaturequalificationisanongoingpartofthecharg-ingprocess,ifanexternalthermistornetworkisdetectedbytheLTC4011.Shouldprescribedtemperaturelimitsbeexceededduringanyparticularchargingstate,chargingwouldbesuspendeduntilthesensedtemperaturereturnedtoanacceptablerange.

Battery-ControlledCharging

BecauseoftheprogrammingarrangementoftheLTC4011,itmaybepossibletoconfigureitforbattery-controlledcharging.Inthiscase,thebatterypackisdesignedtoprovidecustomizedinformationtoanLTC4011-basedcharger,allowingasingledesigntoserviceawiderangeofapplicationbatteries.Assumethechargerisdesignedtoprovideamaximumchargecurrentof800mA(RSENSE=125mΩ).Figure11showsa4-cellNiCdbatterypackforwhich800mArepresentsa0.75Crate.Whenconnectedtothecharger,thispackwouldprovidebatterytempera-tureinformationandcorrectlyconfigurebothfastchargeterminationparametersandtimelimitsfortheinternalNiCdcells.

LTC4011

��4011fb

applicaTions inForMaTion

Asecondpossibility is toconfigureanLTC4011-basedchargertoacceptbatterypackswithvaryingnumbersofcells.ByincludingR2oftheaveragecellvoltagedividernetworkshowninFigure3,battery-basedprogrammingof thenumberofseries-stackedcellscouldberealizedwithoutdefeatingLTC4011detectionofbatteryinsertionorremoval.Figure12showsa2-cellNiMHbatterypackthatprogramsthecorrectnumberofseriescellswhenitisconnectedtothecharger,alongwithindicatingchemistryandprovidingtemperatureinformation.

Anyofthesebatterypackchargecontrolconceptscouldbecombinedinavarietyofwaystoservicecustomapplicationneeds.Chargingparallelcellsisnotrecommended.

PCBLayoutConsiderations

To prevent magnetic and electrical field radiation andhighfrequencyresonantproblems,properlayoutofthecomponentsconnectedtotheLTC4011isessential.RefertoFigure13.Formaximumefficiency, theswitchnoderiseand fall timesshouldbeminimized.The followingPCBdesignprioritylistwillhelpensurepropertopology.LayoutthePCBusingthisspecificorder.

1. InputcapacitorsshouldbeplacedascloseaspossibletoswitchingFETsupplyandgroundconnectionswiththe shortest copper traces possible. The switchingFETsmustbeonthesamelayerofcopperastheinput

Figure11.NiCdBatteryPackwithTimeLimitControl

Figure10.ChargingWaveformsExample

(PAUSE)

READY

CHRG

TOC

7

1200mAhrNiCd CELLS

BATTERYPACK

VTEMP

4

CHEM

10

TIMER

NC66.5k

4011 F11

+

–

10kNTC

Figure12.NiMHBatteryPackIndicatingNumberofCells

7

1500mAhrNiMH CELLS

BATTERYPACK

VTEMP

8

VCELL

R2

4

CHEM

4011 F12

+

–

10kNTC

LTC4011

��4011fb

capacitors.Vias shouldnotbeused tomake theseconnections.

2. Place the LTC4011 close to the switching FETgateterminals, keeping the connecting traces short toproducecleandrivesignals.ThisrulealsoappliestoICsupplyandgroundpinsthatconnecttotheswitchingFETsourcepins.TheICcanbeplacedontheoppositesideofthePCBfromtheswitchingFETs.

3. Placetheinductor inputascloseaspossibletothedrainoftheswitchingFETs.Minimizethesurfaceareaoftheswitchnode.Makethetracewidththeminimumneededtosupporttheprogrammedchargecurrent.Usenocopperfillsorpours.Avoidrunningthecon-nectiononmultiplecopperlayersinparallel.Minimizecapacitancefromtheswitchnodetoanyothertraceorplane.

4. Placethechargecurrentsenseresistorimmediatelyadjacenttotheinductoroutput,andorientitsuchthatcurrentsensetracestotheLTC4011areshort.Thesefeedbacktracesneedtoberuntogetherasasinglepairwiththesmallestspacingpossibleonanygivenlayeronwhichtheyarerouted.LocateanyfiltercomponentonthesetracesnexttotheLTC4011,andnotatthesenseresistorlocation.

5. Placeoutputcapacitorsadjacenttothesenseresisitoroutputandground.

6. Outputcapacitorgroundconnectionsmustfeedintothesamecopperthatconnectstotheinputcapacitorgroundbeforetyingbackintosystemground.

7. Connectionof switchingground tosystemground,oranyinternalgroundplaneshouldbesingle-point.Ifthesystemhasaninternalsystemgroundplane,agoodwaytodothisistoclusterviasintoasinglestarpointtomaketheconnection.

8. RouteanaloggroundasatracetiedbacktotheLTC4011GNDpinbeforeconnectingtoanyotherground.Avoidusingthesystemgroundplane.AusefulCADtechniqueistomakeanaloggroundaseparategroundnetandusea0Ωresistortoconnectanaloggroundtosystemground.

9. Agoodruleof thumbforviacount inagivenhighcurrentpathistouse0.5Apervia.Beconsistentwhenapplyingthisrule.

10.Ifpossible,placeallthepartslistedaboveonthesamePCBlayer.

11.Copperfillsorpoursaregoodforallpowerconnec-tionsexceptasnotedaboveinRule3.Copperplanesonmultiplelayerscanalsobeusedinparallel.Thishelpswiththermalmanagementandlowerstracein-ductance,whichfurtherimprovesEMIperformance.

12.For best current programming accuracy, provide aKelvin connection from RSENSE to SENSE and BAT.SeeFigure14foranexample.

13.ItisimportanttominimizeparasiticcapacitanceontheTIMER,SENSEandBATpins.Thetracesconnectingthesepinstotheirrespectiveresistorsshouldbeasshortaspossible.

Figure13.HighSpeedSwitchingPath

4011 F13

VBAT

L1

VIN

HIGHFREQUENCY

CIRCULATINGPATH

BAT

SWITCH NODE

CIN

SWITCHING GROUND

COUTD1

Figure14.KelvinSensingofChargeCurrent

SENSE

4011 F14

DIRECTION OF CHARGING CURRENT

RSENSE

BAT

applicaTions inForMaTion

LTC4011

��4011fb

package DescripTion

FE20 (CB) TSSOP 0204

0.09 – 0.20(.0035 – .0079)

0° – 8°

0.25REF

RECOMMENDED SOLDER PAD LAYOUT

0.50 – 0.75(.020 – .030)

4.30 – 4.50*(.169 – .177)

1 3 4 5 6 7 8 9 10

111214 13

6.40 – 6.60*(.252 – .260)

3.86(.152)

2.74(.108)

20 1918 17 16 15

1.20(.047)MAX

0.05 – 0.15(.002 – .006)

0.65(.0256)

BSC0.195 – 0.30

(.0077 – .0118)TYP

2

2.74(.108)

0.45 ±0.05

0.65 BSC

4.50 ±0.10

6.60 ±0.10

1.05 ±0.10

3.86(.152)

MILLIMETERS(INCHES) *DIMENSIONS DO NOT INCLUDE MOLD FLASH. MOLD FLASH

SHALL NOT EXCEED 0.150mm (.006") PER SIDE

NOTE:1. CONTROLLING DIMENSION: MILLIMETERS

2. DIMENSIONS ARE IN

3. DRAWING NOT TO SCALE

SEE NOTE 4

4. RECOMMENDED MINIMUM PCB METAL SIZE FOR EXPOSED PAD ATTACHMENT

6.40(.252)BSC

FEPackage20-LeadPlasticTSSOP(4.4mm)(ReferenceLTCDWG#05-08-1663)

ExposedPadVariationCB

LTC4011

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Information furnished by Linear Technology Corporation is believed to be accurate and reliable.However,noresponsibilityisassumedforitsuse.LinearTechnologyCorporationmakesnorepresenta-tionthattheinterconnectionofitscircuitsasdescribedhereinwillnotinfringeonexistingpatentrights.

revision hisToryREV DATE DESCRIPTION PAGENUMBER

B 01/10 ChangestoTypicalApplicationUpdatedOrderInformationSectionChangestoElectricalCharacteristicsChangestoOperationSectionChangestoApplicationsInformation

ChangestoFigures6,7,8,9

12

2,3,412,13,1415,16,19,

21,2219,20

(RevisionhistorybeginsatRevB)

LTC4011

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Linear Technology Corporation1630 McCarthy Blvd., Milpitas, CA 95035-7417(408)432-1900●FAX:(408)434-0507●www.linear.com LINEAR TECHNOLOGY CORPORATION 2005

LT 0110 REV B • PRINTED IN USA

PARTNUMBER DESCRIPTION COMMENTS

LT®1510 Constant-Voltage/Constant-CurrentBatteryCharger Upto1.5AChargeCurrentforLi-Ion,NiCdandNiMHBatteries

LT1511 3AConstant-Voltage/Constant-CurrentBatteryCharger HighEfficiency,MinimumExternalComponentstoFastChargeLithium,NiMHandNiCdBatteries

LT1513 SEPICConstant-orProgrammable-Current/Constant-VoltageBatteryCharger

ChargerInputVoltageMaybeHigher,EqualtoorLowerthanBatteryVoltage,500kHzSwitchingFrequency

LTC1760 SmartBatterySystemManager AutonomousPowerManagementandBatteryChargingforTwoSmartBatteries,SMBusRev1.1Compliant

LTC1960 DualBatteryCharger/SelectorwithSPI 11-BitV-DAC,0.8%VoltageAccuracy,10-BitI-DAC,5%CurrentAccuracy

LTC4008 HighEfficiency,ProgrammableVoltage/CurrentBatteryCharger

Constant-Current/Constant-VoltageSwitchingRegulator,ResistorVoltage/CurrentProgramming,ACAdapterCurrentLimitandThermistorSensorandIndicatorOutputs

LTC4010 HighEfficiencyStandaloneNickelBatteryCharger CompleteNiMH/NiCdChargerinaSmall16-PinPackage,Constant-CurrentSwitchingRegulator

LTC4060 StandaloneLinearNiMH/NiCdFastCharger CompleteNiMH/NiCdChargerinaSmallLeadedorLeadless16-PinPackage,NoSenseResistororBlockingDiodeRequired

LTC4100 SmartBatteryChargerController Level2ChargerOperateswithorwithoutMCUHost,SMBusRev.1.1Compliant

LTC4150 CoulombCounter/BatteryGasGauge HighSideSenseofChargeQuantityandPolarityina10-PinMSOP

LTC4411 2.6ALowLossIdealDiode NoExternalMOSFET,AutomaticSwitchingBetweenDCSources,Simplified,140mΩOnResistance,ThinSOT™Package

LTC4412/LTC4412HV

LowLossPowerPathControllers VeryLowLossReplacementforPowerSupplyORingDiodesUsingMinimalExternalComponents,3V≤VIN≤28V,(3V≤VIN≤36VforHV)

LTC4413 Dual2.6A,2.5Vto5.5V,IdealDiodes LowLossReplacementforORingDiodes,100mΩOnResistance

ThinSOTisatrademarkofLinearTechnologyCorporation.

relaTeD parTs