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LTC4011 High Efficiency Standalone Nickel Battery Charger FeaTures
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DescripTion
TheLTC(R)4011providesacomplete,cost-effectivenickel batteryfastchargesolutioninasmallpackageusingfew external components. A 550kHz PWM current source controllerandallnecessarychargeinitiation,monitoring andterminationcontrolcircuitryareincluded. The LTC4011 automatically senses the presence of a DC adapter and battery insertion or removal. Heavily discharged batteries are precharged with a trickle current.TheLTC4011cansimultaneouslyuseboth-Vand T/tfastchargeterminationtechniquesandcandetect various battery faults. If necessary, a top-off charge is automaticallyappliedtoNiMHbatteriesafterfastchargingiscompleted.TheICwillalsoresumechargingifthe batteryself-dischargesafterafullchargecycle. AllLTC4011chargingoperationsarequalifiedbyactual chargetimeandmaximumaveragecellvoltage.Charging mayalsobegatedbyminimumandmaximumtemperature limits.NiMHorNiCdfastchargeterminationparameters arepin-selectable. Integrated PowerPath control support ensures that the systemremainspoweredatalltimeswithoutallowingload transientstoadverselyaffectchargetermination.
CompleteNiMH/NiCdChargerfor1to16Cells NoMicrocontrollerorFirmwareRequired 550kHzSynchronousPWMCurrentSourceController NoAudibleNoisewithCeramicCapacitors PowerPathTMControlSupport ProgrammableChargeCurrent:5%Accuracy WideInputVoltageRange:4.5Vto34V AutomaticTricklePrecharge -VFastChargeTermination OptionalT/tFastChargeTermination AutomaticNiMHTop-OffCharge ProgrammableTimer AutomaticRecharge MultipleStatusOutputs MicropowerShutdown 20-LeadThermallyEnhancedTSSOPPackage
applicaTions
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IntegratedorStandaloneBatteryCharger PortableInstrumentsorConsumerProducts Battery-PoweredDiagnosticsandControl Back-UpBatteryManagement
L,LT,LTC,LTM,LinearTechnologyandtheLinearlogoareregisteredtrademarksofLinear TechnologyCorporation.PowerPathisatrademarkofLinearTechnologyCorporation.Allother trademarksarethepropertyoftheirrespectiveowners.
Typical applicaTion
2ANiMHBatteryCharger
FROM ADAPTER 5V INFET FAULT CHRG TOC READY 10F
2ANiMHChargeCycleat1C
4.7H
10F
0.1F
0.033F
0.068F
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LTC4011 absoluTe MaxiMuM raTings
VCC (Input Supply) to GND......................... -0.3V to 36V DCIN to GND .............................................. -0.3V to 36V FAULT, CHRG, VCELL, VCDIV, SENSE, BAT, TOC or READY to GND ........................... -0.3V to VCC + 0.3V SENSE to BAT ........................................................0.3V CHEM, VTEMP or TIMER to GND................ -0.3V to 3.5V PGND to GND.........................................................0.3V Operating Ambient Temperature Range (Note 2)........................................................ 0C to 85C Operating Junction Temperature (Note 3) ............. 125C Storage Temperature Range...................- 65C to 150C Lead Temperature (Soldering, 10 sec) .................. 300C
(Note 1)
pin conFiguraTion
TOP VIEW DCIN FAULT CHRG CHEM GND VRT VTEMP VCELL VCDIV 1 2 3 4 5 6 7 8 9 21 20 INFET 19 READY 18 VCC 17 TGATE 16 PGND 15 BGATE 14 INTVDD 13 TOC 12 BAT 11 SENSE
TIMER 10
FE PACKAGE 20-LEAD PLASTIC TSSOP TJMAX=125C,JA=38C/W EXPOSEDPAD(PIN21)ISGND,MUSTBESOLDEREDTOPCB TOOBTAINSPECIFIEDTHERMALRESISTANCE
orDer inForMaTion
LEADFREEFINISH LTC4011CFE#PBF LEADBASEDFINISH LTC4011CFE TAPEANDREEL LTC4011CFE#TRPBF TAPEANDREEL LTC4011CFE#TR PARTMARKING LTC4011CFE PARTMARKING LTC4011CFE PACKAGEDESCRIPTION 20-LeadPlasticTSSOP PACKAGEDESCRIPTION 20-LeadPlasticTSSOP TEMPERATURERANGE 0Cto85C TEMPERATURERANGE 0Cto85C
ConsultLTCMarketingforpartsspecifiedwithwideroperatingtemperatureranges. Formoreinformationonleadfreepartmarking,goto:http://www.linear.com/leadfree/ Formoreinformationontapeandreelspecifications,goto:http://www.linear.com/tapeandreel/
elecTrical characTerisTics
SYMBOL VCC Supply VCC ISHDN IQ ICC VUVLO VUV(HYST) VSHDNI VSHDND VCE VDD IDD Input Voltage Range Shutdown Quiescent Current (Note 5) Quiescent Current Operating Current Undervoltage Threshold Voltage Undervoltage Hysteresis Voltage Shutdown Threshold Voltage Shutdown Threshold Voltage Charge Enable Threshold Voltage Output Voltage Short-Circuit Current (Note 6) PARAMETER
(Note 4) The indicates specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25C. VCC = 12V, BAT = 4.8V, GND = PGND = 0V, unless otherwise noted.
CONDITIONS
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MIN 4.5
TYP
MAX 34
UNITS V A mA mA V mV mV mV mV V mA V
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VCC = BAT = 4.8V Waiting to Charge (Pause) Fast Charge State, No Gate Load VCC Increasing DCIN - VCC, DCIN Increasing DCIN - VCC, DCIN Decreasing VCC - BAT, VCC Increasing No Load INTVDD = 0V VCC = 4.5V, IDD = -10mA
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5 3 5 3.85 5 -60 400 4.5 -100 3.85 4.2 170
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10 5 9 4.45 60 -5 600 5.5 -10
30 -25 510 5 -50
INTVDD Regulator
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INTVDD(MIN) Output Voltage
LTC4011 elecTrical characTerisTics
SYMBOL VRT IRT VFS VPC VTC VLI IBAT ISENSE IOFF fTYP fMIN DCMAX VOL(TG) VOH(TG) tR(TG) tF(TG) VOL(BG) VOH(BG) tR(BG) tF(BG) ADC Inputs ILEAK VBP VBOV VMFC VFCBF VTERM VAR TTERM TMIN TMAXI Analog Channel Leakage Battery Present Threshold Voltage Battery Overvoltage Minimum Fast Charge Voltage Fast Charge Battery Fault Voltage -V Termination Automatic Recharge Voltage TTermination(Note8) Minimum Charging Temperature (Note 8) Maximum Charge Initiation Temperature (Note 8) CHEM OPEN (NiCd) CHEM = 0V (NiMH) VCELL Decreasing CHEM = 3.3V (NiCd) CHEM = 0V (NiMH) VTEMP Increasing VTEMP Decreasing, Not Charging 0V < VCELL < 2V, 550mV < VTEMP < 2V

The indicates specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25C. VCC = 12V, BAT = 4.8V, GND = PGND = 0V, unless otherwise noted.
PARAMETER Output Voltage Short-Circuit Current BAT - SENSE Full-Scale Regulation Voltage (Fast Charge) CONDITIONS RL = 10k VRT = 0V 0.3V < BAT < VCC - 0.3V (Note 5) BAT = 4.8V MIN 3.075 3 -9 95 95 16 16 6.5 6.5 -2 50

TYP 3.3
MAX 3.525 3.6 -1
UNITS V V mA mV mV mV mV mV mV mV mA A A kHz kHz %
Thermistor Termination

PWM Current Source

100 100 20 20 10 10 0.3
105 105 24 24 13.5 13.5 2 150 1 640
BAT - SENSE Precharge Regulation Voltage 0.3V < BAT < VCC - 0.3V (Note 5) BAT = 4.8V BAT - SENSE Top-Off Charge Regulation Voltage BAT - SENSE Line Regulation BAT Input Bias Current SENSE Input Bias Current Input Bias Current Typical Switching Frequency Minimum Switching Frequency Maximum Duty Cycle TGATE Output Voltage Low (VCC - TGATE, Note 7) TGATE Output Voltage High TGATE Rise Time TGATE Fall Time BGATE Output Voltage Low BGATE Output Voltage High BGATE Rise Time BGATE Fall Time VCC > 9V, No Load VCC < 7V, No Load VCC - TGATE, No Load CLOAD = 3nF, 10% to 90% CLOAD = 3nF, 10% to 90% No Load No Load CLOAD = 1.6nF, 10% to 90% CLOAD = 1.6nF, 10% to 90% 0.3V < BAT < VCC - 0.3V (Note 5) BAT = 4.8V 5.5V < VCC < 25V, Fast Charge 0.3V < BAT < VCC - 0.1V SENSE = BAT SENSE or BAT, VCELL = 0V
-1 460 20 98 5 VCC-0.5
0 550 30 99 5.6 VCC 0 35 45

8.75 50 100 100 50 80 80
V V mV ns ns mV V ns ns nA
INTVDD-0.075
0 INTVDD 35 15 100 320 1.815 850 1.17 16 6 1.260 1.3 0.5 0 41.5 350 1.95 900 1.22 20 10 1.325 2 1 5 45
Charger Thresholds 370 2.085 950 1.27 25 14 1.390 2.7 1.5 9 47 mV V mV V mV mV V C/min C/min C C
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LTC4011 elecTrical characTerisTics
SYMBOL TMAXC VTEMP(D) VTEMP(P) tTIMER tMAX VFR VOL(INFET) VOH(INFET) tOFF(INFET) VOL ILKG IIH(VCDIV) VIL VIH IIL IIH PARAMETER Maximum Fast Charge Temperature (Note 8) VTEMP Disable Threshold Voltage Pause Threshold Voltage Internal Time Base Error Programmable Timer Error INFET Forward Regulation Voltage Output Voltage Low Output Voltage High INFET OFF Delay Time Output Voltage Low (ILOAD = 10mA) Output Leakage Current Input Current High Input Voltage Low Input Voltage High Input Current Low Input Current High RTIMER = 49.9k DCIN - VCC VCC - INFET, No Load VCC - INFET, No Load CLOAD = 10nF, INFET to 50% VCDIV All Other Status Outputs All Status Outputs Inactive, VOUT = VCC VCDIV = VBAT (Shutdown) CHEM (NiMH) CHEM (NiCd) CHEM = GND CHEM = 3.3V

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

MIN 57 2.8 130 -10 -20 15 3.75
TYP 60
MAX 63 3.3 280 10 20
UNITS C V mV % % mV V mV s mV mV A A mV V A A
Charger Timing

PowerPath Control

55 5.2 0 3 435 300
100 7 50 15 700 600 10 1 900
Status and Chemistry Select
-10 -1 2.85 -20 -20
-5 20
Note1:StressesbeyondthoselistedunderAbsoluteMaximumRatings maycausepermanentdamagetothedevice.ExposuretoanyAbsolute MaximumRatingconditionforextendedperiodsmayaffectdevice reliabilityandlifetime. Note2:TheLTC4011Cisguaranteedtomeetperformancespecifications from0Cto70C.Specificationsoverthe0Cto85Coperating temperaturerangeareassuredbydesign,characterizationandcorrelation withstatisticalprocesscontrols. Note3:OperatingjunctiontemperatureTJ(inC)iscalculatedfrom theambienttemperatureTAandthetotalcontinuouspackagepower dissipationPD(inwatts)bytheformula: TJ=TA+JA*PD RefertotheApplicationsInformationsectionfordetails.ThisICincludes overtemperatureprotectionthatisintendedtoprotectthedeviceduring momentaryoverloadconditions.Junctiontemperaturewillexceed125C
whenovertemperatureprotectionisactive.Continuousoperationabove thespecifiedmaximumoperatingjunctiontemperaturemayresultin devicedegradationorfailure. Note4:Allcurrentintodevicepinsispositive.Allcurrentoutofdevice pinsisnegative.AllvoltagesarereferencedtoGND,unlessotherwise specified. Note5:Theselimitsareguaranteedbycorrelationtowaferlevel measurements. Note6:Outputcurrentmaybelimitedbyinternalpowerdissipation.Refer totheApplicationsInformationsectionfordetails. Note7:EitherTGATEVOHmayapplyfor7.5V4011fb
LTC4011 Typical perForMance characTerisTics
NiCdChargeCycleat1C NiCdChargeCycleat2C
NiMHChargeCycleat0.5C
BatteryPresentThresholdVoltage (perCell)
MinimumFastChargeThreshold Voltage(perCell)
AutomaticRechargeThreshold Voltage(perCell)
BatteryOvervoltageThreshold Voltage(perCell)
-VTerminationVoltage(perCell)
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LTC4011 Typical perForMance characTerisTics
ProgrammableTimerAccuracy ChargeCurrentAccuracy PWMSwitchingFrequency
ChargerEfficiencyatIOUT=2A
ChargerSoft-Start
FastChargeCurrentLine Regulation
FastChargeCurrentOutput Regulation
INFETForwardRegulationVoltage
INFETOFFDelayTime
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LTC4011 Typical perForMance characTerisTics
PowerPathSwitching ShutdownQuiescentCurrent PWMInputBiasCurrent(OFF)
100s/DIV
UndervoltageLockoutThreshold Voltage
CURRENT (A)
ShutdownThresholdVoltage (DCIN-VCC)
CURRENT (A)
ChargeEnableThresholdVoltage (VCC-BAT)
ThermistorDisableThreshold Voltage
PauseThresholdVoltage
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LTC4011 Typical perForMance characTerisTics
INTVDDVoltage INTVDDShort-CircuitCurrent
pin FuncTions
DCIN(Pin1):DCPowerSenseInput.TheLTC4011senses voltage on this pin to determine when an external DC powersourceispresent.Thisinputshouldbeisolated fromVCCbyablockingdiodeorPowerPathFET.Referto theApplicationsInformationsectionforcompletedetails. OperatingvoltagerangeisGNDto34V. FAULT (Pin 2): Active-Low Fault Indicator Output. The LTC4011indicatesvariousbatteryandinternalfaultconditionsbyconnectingthispintoGND.RefertotheOperation andApplicationsInformationsectionsforfurtherdetails. ThisoutputiscapableofdrivinganLEDandshouldbe leftfloatingifnotused.FAULTisanopen-drainoutputto GNDwithanoperatingvoltagerangeofGNDtoVCC. CHRG(Pin3):Active-LowChargeIndicatorOutput.The LTC4011indicatesitisprovidingchargetothebatteryby connectingthispintoGND.RefertotheOperationand ApplicationsInformationsectionsforfurtherdetails.This output is capableof drivingan LED and should be left floatingifnotused.CHRGisanopen-drainoutputtoGND withanoperatingvoltagerangeofGNDtoVCC. CHEM (Pin 4): BatteryChemistrySelectionInput. This pinshouldbewiredtoGNDtoselectNiMHfastcharge terminationparameters.Ifavoltagegreaterthan2.85Vis appliedtothispin,oritisleftfloating,NiCdparameters areused.RefertotheApplicationsInformationsectionfor furtherdetails.OperatingvoltagerangeisGNDto3.3V. GND (Pin 5): Ground. This pin provides a single-point groundforinternalreferencesandothercriticalanalog circuits. VRT(Pin6):ThermistorNetworkTerminationOutput.The LTC4011provides3.3Vonthispintodriveanexternal thermistor network connected between VRT, VTEMP and GND.Additionalpowershouldnotbedrawnfromthispin bythehostapplication. VTEMP(Pin7):BatteryTemperatureInput.Anexternal thermistornetworkmaybeconnectedtoVTEMPtoprovide temperature-based charge qualification and additional fastchargeterminationcontrol.Chargingmayalsobe pausedbyconnectingtheVTEMPpintoGND.Referto theOperationandApplicationsInformationsectionsfor complete details on external thermistor networks and chargecontrol.Ifthispinisnotuseditshouldbewired toVRT.OperatingvoltagerangeisGNDto3.3V. VCELL(Pin8):AverageSingle-CellVoltageInput.AnexternalvoltagedividerbetweenBATandVCDIVisattachedto thispintomonitortheaveragesingle-cellvoltageofthe batterypack.TheLTC4011usesthisinformationtoprotect againstcatastrophicbatteryovervoltageandtocontrol thechargingstate.RefertotheApplicationsInformation sectionforfurtherdetailsontheexternaldividernetwork. OperatingvoltagerangeisGNDtoBAT.
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LTC4011 pin FuncTions
VCDIV(Pin9):AverageCellVoltageResistorDividerTermination.TheLTC4011connectsthispintoGNDprovidedthe chargerisnotinshutdown.VCDIVisanopen-drainoutput toGNDwithanoperatingvoltagerangeofGNDtoBAT. TIMER(Pin10):ChargeTimerInput.Aresistorconnected betweenTIMERandGNDprogramschargecycletiming limits.RefertotheApplicationsInformationsectionfor completedetails.OperatingvoltagerangeisGNDto1V. SENSE(Pin11):ChargeCurrentSenseInput.Anexternal resistorbetweenthisinputandBATisusedtoprogram charge current. Refer to the Applications Information section for complete details on programming charge current.Operatingvoltagerangesfrom(BAT-50mV)to (BAT+200mV). BAT(Pin12):BatteryPackConnection.TheLTC4011uses thevoltageonthispintocontrolcurrentsourcedfrom VCCtothebatteryduringcharging.Allowableoperating voltagerangeisGNDtoVCC. TOC(Pin13):Active-LowTop-OffChargeIndicatorOutput.TheLTC4011indicatesthetop-offchargestatefor NiMHbatteriesbyconnectingthispintoGND.Referto theOperationandApplicationsInformationsectionsfor furtherdetails.ThisoutputiscapableofdrivinganLED andshouldbeleftfloatingifnotused.TOCisanopendrainoutputtoGNDwithanoperatingvoltagerangeof GNDtoVCC. INTVDD(Pin14):Internal5VRegulatorOutput.Thispin providesameansofbypassingtheinternal5Vregulator usedtopowertheBGATEoutputdriver.Typically,power should not be drawn from this pin by the application circuit.RefertotheApplicationInformationsectionfor additionaldetails. BGATE(Pin15):ExternalSynchronousN-channelMOSFET GateControlOutput.Thisoutputprovidesgatedriveto anoptionalexternalNMOSpowertransistorswitchused forsynchronousrectificationtoincreaseefficiencyinthe step-downDC/DCconverter.OperatingvoltageisGNDto INTVDD.BGATEshouldbeleftfloatingifnotused. PGND(Pin16):PowerGround.Thispinprovidesareturn forswitchingcurrentsgeneratedbyinternalLTC4011circuits.Externally,PGNDandGNDshouldbewiredtogether using a very low impedance connection. Refer to PCB Layout Considerations in the Applications Information sectionforadditionalgroundingdetails. TGATE(Pin17):ExternalP-channelMOSFETGateControl Output.ThisoutputprovidesgatedrivetoanexternalPMOS powertransistorswitchusedintheDC/DCconverter.OperatingvoltagerangevariesasafunctionofVCC.Referto theElectricalCharacteristicstableforspecificvoltages. VCC(Pin18):PowerInput.ExternalPowerPathcontrol circuitsnormallyconnecteithertheDCinputpowersupplyorthebatterytothispin.RefertotheApplications Informationsectionforfurtherdetails.Suggestedapplied voltagerangeisGNDto34V. READY (Pin 19): Active-Low Ready-to-Charge Output. TheLTC4011connectsthispintoGNDifproperoperating voltagesforchargingarepresent.RefertotheOperation sectionforcompletedetailsonchargequalification.This output is capableof drivingan LED and should be left floatingifnotused.READYisanopen-drainoutputto GNDwithanoperatingvoltagerangeofGNDtoVCC. INFET(Pin20):PowerPathControlOutput.Forverylow dropoutapplications,thisoutputmaybeusedtodrive the gate of an input PMOS pass transistor connected betweentheDCinput(DCIN)andtherawsystemsupply rail(VCC).INFETisinternallyclampedabout6VbelowVCC. MaximumoperatingvoltageisVCC.INFETshouldbeleft floatingifnotused. Exposed Pad (Pin 21): This pin provides enhanced thermalpropertiesfortheTSSOP .Itmustbesoldered tothePCBcoppergroundtoobtainoptimumthermal performance.
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LTC4011 block DiagraM
1 2 3 4 DCIN FAULT CHRG CHEM THERMISTOR INTERFACE CHARGER STATE CONTROL LOGIC UVLO AND SHUTDOWN INFET FET DIODE READY VCC 20 19 18
5 GND 6 7 8 VRT VTEMP VCELL
TGATE PGND BGATE PWM BAT SENSE
17 16 15 12 11
A/D CONVERTER
BATTERY DETECTOR 9 10 VCDIV TIMER CHARGE TIMER VOLTAGE REGULATOR INTVDD TOC 14 13
VOLTAGE REFERENCE
INTERNAL VOLTAGE REGULATOR
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0
LTC4011 operaTion
Figure1.LTC4011StateDiagram
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LTC4011 operaTion
ShutdownState TheLTC4011remainsinmicropowershutdownuntilDCIN (Pin1)isdrivenaboveVCC(Pin18).Inshutdownallstatus andPWMoutputsandinternallygeneratedterminations orsupplyvoltagesareinactive.Currentconsumptionfrom VCCandBATisreducedtoaverylowlevel. ChargeQualificationState Once DCIN is greater than VCC, the LTC4011 exits micropowershutdown,enablesitsowninternalsupplies, providesVRTvoltagefortemperaturesensing,andswitches VCDIVtoGNDtoallowmeasurementoftheaveragesinglecellvoltage.TheICalsoverifiesthatVCCisatorabove4.2V, VCCis510mVaboveBATandVCELLisbetween350mVand 1.95V.IfVCELLisbelow350mV,nochargingwilloccur,and ifVCELLisabove1.95V,thefaultstateisentered,which isdescribedinmoredetailbelow.Onceadequatevoltage conditionsexistforcharging,READYisasserted. IfthevoltagebetweenVTEMPandGNDisbelow200mV,the LTC4011ispaused.IfVTEMPisabove200mVbutbelow 2.85V,theLTC4011verifiesthatthesensedtemperatureis between5Cand45C.Ifthesetemperaturelimitsarenot metorifitsowndietemperatureistoohigh,theLTC4011 willindicateafaultandnotallowchargingtobegin.IfVTEMP isgreaterthan2.85V,batterytemperaturerelatedcharge qualification,monitoringandterminationaredisabled. Oncechargingisfullyqualified,prechargebegins(unless the LTC4011 is paused). In that case, the VTEMP pin is monitoredforfurthercontrol.Thechargestatusindicators andPWMoutputsremaininactiveuntilchargingbegins. ChargeMonitoring TheLTC4011continuestomonitorimportantvoltageand temperatureparametersduringallchargingstates.Ifthe DCinputisremoved,chargingstopsandtheshutdown stateisentered.IfVCCdropsbelow4.25VorVCELLdrops below350mV,chargingstopsandtheLTC4011returns tothechargequalificationstate.IfVCELLexceeds1.95V, chargingstopsandtheICentersthefaultstate.Ifanexternal thermistorindicatessensedtemperatureisbeyondarange of5Cto60C,ortheinternaldietemperatureexceedsan internalthermallimit,chargingissuspended,thecharge timerispausedandtheLTC4011indicatesafaultcondition.
(RefertoFigure1)
Normalchargingresumesfromthepreviousstatewhen thesensedtemperaturereturnstoasatisfactoryrange.In addition,otherbatteryfaultsaredetectedduringspecific chargingstatesasdescribedbelow. PrechargeState IftheinitialvoltageonVCELLisbelow900mV,theLTC4011 enterstheprechargestateandenablesthePWMcurrent sourcetotricklechargeusingone-fifththeprogrammed chargecurrent.TheCHRGstatusoutputisactiveduring precharge. The precharge state duration is limited to tMAX/12minutes,wheretMAXisthemaximumfastcharge periodprogrammedwiththeTIMERpin.IfsufficientVCELL voltagecannotbedevelopedinthislengthoftime,thefault stateisentered,otherwisefastchargebegins. FastChargeState Ifadequateaveragesingle-cellvoltageexists,theLTC4011 entersthefastchargestateandbeginschargingatthe programmed current set by the external current sense resistor connected between the SENSE and BAT pins. TheCHRGstatusoutputisactiveduringfastcharge.If VCELLisinitiallyabove1.325V,voltage-basedtermination processingbeginsimmediately.Otherwise-Vtermination isdisabledforastabilizationperiodoftMAX/12.Inthat case,theLTC4011makesanotherfaultcheckattMAX/12, requiringtheaveragecellvoltagetobeabove1.22V.This ensures the battery pack is accepting a fast charge. If VCELLisnotabovethisvoltagethreshold,thefaultstateis entered.FastchargestatedurationislimitedtotMAXand thefaultstateisenteredifthislimitisexceeded. ChargeTermination Fastchargeterminationparametersaredependentupon thebatterychemistryselectedwiththeCHEMpin.Voltagebasedtermination(-V)isalwaysactiveaftertheinitial voltagestabilizationperiod.Ifanexternalthermistornetwork ispresent,chemistry-specificlimitsforT/t(rateoftemperaturerise)arealsousedintheterminationalgorithm. Temperature-basedtermination,ifenabled,becomesactive as soon as the fast charge state is entered. Successful chargeterminationrequiresachargeratebetweenC/2and 2C.Lowerratesmaynotproducethebatteryvoltageand temperatureprofilerequiredforchargetermination.
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LTC4011 operaTion
Top-OffChargeState IfNiMHfastchargeterminationoccursbecausethe T/tlimitisexceededafteraninitialperiodoftMAX/12 hasexpired,theLTC4011entersthetop-offchargestate. Top-offchargeisimplementedbysourcingone-tenththe programmedchargecurrentfortMAX/3minutestoensure that100%chargehasbeendeliveredtothebattery.The CHRGandTOCstatusoutputsareactiveduringthetop-off state.IfNiCdcellshavebeenselectedwiththeCHEMpin, theLTC4011neverentersthetop-offstate. AutomaticRechargeState Oncechargingiscomplete,theautomaticrechargestate isenteredtoaddresstheself-dischargecharacteristics ofnickelchemistrycells.Thechargestatusoutputsare inactive during automatic recharge, but VCDIV remains switchedtoGNDtomonitortheaveragecellvoltage.Ifthe VCELLvoltagedropsbelow1.325Vwithoutfallingbelow 350mV,thechargetimerisresetandanewfastcharge cycleisinitiated. TheinternalterminationalgorithmsoftheLTC4011are adjustedwhenafastchargecycleisinitiatedfromautomaticrecharge,becausethebatteryshouldbealmostfully charged.Voltage-basedterminationisenabledimmediately andtheNiMHT/tlimitisfixedatabatterytemperature riseof1C/minute. FaultState Asdiscussedpreviously,theLTC4011entersthefaultstate basedondetectionofinvalidbatteryvoltagesduringvariouschargingphases.TheICalsomonitorstheregulation ofthePWMcontrolloopandwillenterthefaultstateif thisisnotwithinacceptablelimits.Onceinthefaultstate, thebatterymustberemovedorDCinputpowermustbe cycled in order to initiate further charging. In the fault state, the FAULT output is active, the READY output is inactive,chargingstopsandthechargeindicatoroutputs areinactive.TheVCDIVoutputremainsconnectedtoGND toallowdetectionofbatteryremoval. NotethattheLTC4011alsousestheFAULToutputtoindicatethatchargingissuspendedduetoinvalidbatteryor internaldietemperatures.However,theICdoesnotenter thefaultstateinthesecasesandnormaloperationwill resumewhenalltemperaturesreturntoacceptablelevels. RefertotheStatusOutputssectionformoredetail. InsertionandRemovalofBatteries TheLTC4011automaticallysensestheinsertionorremoval ofabatterybymonitoringtheVCELLpinvoltage.Should thisvoltagefallbelow350mV,theICconsidersthebatterytobeabsent.Removingandtheninsertingabattery causestheLTC4011toinitiateacompletelynewcharge cyclebeginningwithchargequalification. ExternalPauseControl Afterchargingisinitiated,theVTEMPpinmaybeusedto pauseoperationatanytime.Whenthevoltagebetween VTEMP and GND drops below 200mV, the charge timer pauses,fastchargeterminationalgorithmsareinhibited andthePWMoutputsaredisabled.ThestatusandVCDIV outputsallremainactive.Normalfunctionisfullyrestored fromthepreviousstatewhenpauseends. StatusOutputs TheLTC4011open-drainstatusoutputsprovidevaluable information about the IC's operating state and can be usedforavarietyofpurposesinapplications.Table1 summarizesthestateofthefourstatusoutputsandthe VCDIVpinasafunctionofLTC4011operation.Thestatus outputscandirectlydrivecurrent-limitedLEDsterminated totheDCinput.TheVCDIVcolumninTable1isstrictly informational.VCDIVshouldonlybeusedfortheVCELL resistordivider,aspreviouslydiscussed.
Table1.LTC4011StatusPins
READY FAULT Off On Off Off CHRG Off Off TOC Off Off VCDIV Off On CHARGERSTATE Off ReadytoCharge (VTEMPHeldLow) orAutomaticRecharge PrechargeorFastCharge (MaybePaused) NiMHTop-OffCharge (MaybePaused) TemperatureLimits Exceeded FaultState(Latched)
On On On Off
Off Off On On
On On
Off On
On On On On
OnorOff OnorOff Off Off
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LTC4011 operaTion
PWMCurrentSourceController AnintegralpartoftheLTC4011isthePWMcurrentsource controller. The charger uses a synchronous step-down architecturetoproducehighefficiencyandlimitedthermal dissipation.Thenominaloperatingfrequencyof550kHz allowsuseofasmallerexternalfiltercomponents.The TGATEandBGATEoutputshaveinternallyclampedvoltageswings.Theysourcepeakcurrentstailoredtosmaller surface-mountpowerFETslikelytoappearinapplications providinganaveragechargecurrentof3Aorless.During thevariouschargingstates,theLTC4011usesthePWM controllertoregulateanaveragevoltagebetweenSENSE andBATthatrangesfrom10mVto100mV. AconceptualdiagramoftheLTC4011PWMcontrolloop isshowninFigure2. The voltage across the external current programming resistorRSENSEisaveragedbyintegratingerroramplifier EA.Aninternalprogrammingcurrentisalsopulledfrom inputresistorR1.TheIPROG*R1productestablishesthe desiredaveragevoltagedropacrossRSENSE,andhence, the average current through RSENSE. The ITH output of theerroramplifierisascaledcontrolcurrentfortheinput
VCC P N LTC4011 17 15 11 RSENSE 12 TGATE BGATE SENSE R3 CC Q S R PWM CLOCK
ofthePWMcomparatorCC.TheITH*R3productsetsa peakcurrentthresholdforCCsuchthatthedesiredaveragecurrentthroughRSENSEismaintained.Thecurrent comparatoroutputdoesthisbyswitchingthestateofthe SRlatchattheappropriatetime. Atthebeginningofeachoscillatorcycle,thePWMclock setstheSRlatchandtheexternalP-channelMOSFETis switchedon(N-channelMOSFETswitchedoff)torefresh thecurrentcarriedbytheexternalinductor.Theinductor current and voltage drop across RSENSE begin to rise linearly. During normal operation, the PFET is turned off(NFETon)duringthecyclebyCCwhenthevoltage differenceacrossRSENSEreachesthepeakvaluesetby theoutputofEA.Theinductorcurrentthenrampsdown linearlyuntilthenextrisingPWMclockedge.Thiscloses theloopandmaintainsthedesiredaveragechargecurrent intheexternalinductor. LowDropoutCharging Afterchargingisinitiated,theLTC4011doesnotrequire thatVCCremainatleast500mVaboveBATbecausesituationsexistwherelowdropoutchargingmightoccur.In oneinstance,parasiticseriesresistancemaylimitPWM headroom (between VCC and BAT) as 100% charge is reached.AsecondcasecanarisewhentheDCadapter selectedbytheenduserisnotcapableofdeliveringthe currentprogrammedbyRSENSE,causingtheoutputvoltageoftheadaptertocollapse.Whileinlowdropout,the LTC4011PWMrunsnear100%dutycyclewithafrequency thatmaynotbeconstantandcanbelessthan550kHz. Thechargecurrentwilldropbelowtheprogrammedvalue toavoidgeneratingaudiblenoise,sotheactualcharge delivered to the battery may depend primarily on the LTC4011chargetimer. InternalDieTemperature TheLTC4011providesinternalovertemperaturedetection toprotectagainstelectricaloverstress,primarilyatthe FETdriveroutputs.Ifthedietemperaturerisesabovethis thermallimit,theLTC4011stopsswitchingandindicates afaultaspreviouslydiscussed.
BAT R1
R4
IPROG
Figure2.LTC4011PWMControlLoop
+
4011 F02
R2
-
EA
ITH
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LTC4011 applicaTions inForMaTion
ExternalDCSource TheexternalDCpowersourceshouldbeconnectedtothe chargingsystemandtheVCCpinthrougheitherapower diode or P-channel MOSFET. This prevents catastrophic systemdamageintheeventofaninputshorttogroundor reverse-voltagepolarityattheDCinput.TheLTC4011automaticallysenseswhenthisinputispresent.Theopen-circuit voltageoftheDCsourceshouldbebetween4.5Vand34V, dependingonthenumberofcellsbeingcharged.Inorder toavoidlowdropoutoperation,ensure100%capacityat chargetermination,andallowreliabledetectionofbattery insertion,removalorovervoltage,thefollowingequation canbeusedtodeterminetheminimumfull-loadvoltagethat shouldbeprovidedbytheexternalDCpowersource. DCIN(MIN)=(n*2V)+0.3V wherenisthenumberofseriescellsinthebatterypack. The LTC4011 will properly charge over a wide range of DCIN and BAT voltage combinations. Operating the LTC4011inlowdropoutorwithDCINmuchgreaterthan BATwillforcethePWMfrequencytobemuchlessthan 550kHz.TheLTC4011disableschargingandsetsafault ifalargeDCINtoBATdifferentialwouldcausegeneration ofaudiblenoise. PowerPathControl ProperPowerPathcontrolisanimportantconsideration whenfastchargingnickelcells.Thiscontrolensuresthat thesystemloadremainspoweredatalltimes,butthat normalsystemoperationandassociatedloadtransients donotadverselyaffectfastchargetermination.Forhigh efficiencyandlowdropoutapplications,theLTC4011can providegatedrivefromtheINFETpindirectlytoaninput P-channelMOSFET. Thebatteryshouldalsobeconnectedtotherawsystem supply by a switch that selects the battery for system poweronlyifanexternalDCsourceisnotpresent.Again, forapplicationsrequiringhigherefficiency,aP-channel MOSFETwithitsgatedrivenfromtheDCinputcanbeused toperformthisswitchingfunction(seeFigure8).Gate voltageclampingmaybenecessaryonanexternalPMOS transistorusedinthismannerathigherinputvoltages. Alternatively,adiodecanbeusedinplaceofthisFET. BatteryChemistrySelection Thedesiredbatterychemistryisselectedbyprogramming theCHEMpintothepropervoltage.IfitiswiredtoGND, a set of parameters specific to charging NiMH cells is selected.WhenCHEMisleftfloatingorconnectedtoVRT, chargingisoptimizedforNiCdcells.Thevariouscharging parametersaredetailedinTable2. ProgrammingChargeCurrent Charge current is programmed using the following equation: RSENSE = 100mV IPROG
RSENSE is an external resistor connected between the SENSEandBATpins.A1%resistorwithalowtemperature coefficientandsufficientpowerdissipationcapabilityto avoidself-heatingeffectsisrecommended.Chargerate shouldbebetweenapproximatelyC/2and2C. InductorValueSelection Formanyapplications,10Hrepresentsanoptimumvalue fortheinductorthePWMusestogeneratechargecurrent. For applications with IPROG of 1.5A or greater running fromanexternalDCsourceof15Vorless,valuesbetween 5Hand7.5Hcanoftenbeselected.Forwideroperating conditionsthefollowingequationcanbeusedasaguide forselectingtheminimuminductorvalue. L>6.5*10-6*VDCIN*RSENSE,L4.7H Actualpartselectionshouldaccountforbothmanufacturing toleranceandtemperaturecoefficienttoensurethisminimum.Agoodinitialselectioncanbemadebymultiplying thecalculatedminimumby1.4androundingupordown totheneareststandardinductancevalue. Ultimately,thereisnosubstituteforbenchevaluationof theselectedinductorinthetargetapplication,whichcan alsobeaffectedbyotherenvironmentalfactorssuchas ambient operating temperature. Using inductor values lowerthanrecommendedbytheequationshownabove canresultinafaultconditionatthestartofprechargeor top-offcharge.
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LTC4011 applicaTions inForMaTion
Table2.LTC4011ChargingParameters
STATE PC FC Open GND CHEM PIN BAT CHEMISTRY Both NiCd NiMH TIMER tMAX/12 tMAX tMAX TMIN 5C 5C 5C TMAX 45C 60C 60C ICHRG IPROG/5 IPROG IPROG TERMINATIONCONDITION TimerExpires -20mVperCellor2C/Minute 1.5C/MinuteforFirsttMAX/12MinutesifInitial VCELL <1.325V -10mVperCellor1C/MinuteAftertMAX/12Minutes orifInitialVCELL>1.325V TOC AR GND NiMH Both tMAX/3 5C 5C 60C 45C IPROG/10 TimerExpires 0 VCELL<1.325V
PC: Precharge FC: FastCharge(Initial-VTerminationHoldOffoftMAX/12MinutesMayApply) TOC: Top-OffCharge(OnlyforNiMHT/tFCTerminationAfterInitialtMAX/12Period) AR: AutomaticRecharge(TemperatureLimitsApplytoStateTerminationOnly)
Table3.LTC4011TimeLimitProgrammingExamples
RTIMER 24.9k 33.2k 49.9k 66.5k 100k TYPICALFAST CHARGERATE 2C 1.5C 1C 0.75C C/2 PRECHARGELIMIT (MINUTES) 3.8 5 7.5 10 15 FASTCHARGE VOLTAGESTABILIZATION (MINUTES) 3.8 5 7.5 10 15 FASTCHARGELIMIT (HOURS) 0.75 1 1.5 2 3 TOP-OFF CHARGE (MINUTES) 15 20 30 40 60
ProgrammingMaximumChargeTimes ConnectingtheappropriateresistorbetweentheTIMER pinandGNDprogramsthemaximumdurationofvarious chargingstates.Tosomedegree,thevalueshouldreflect howcloselytheprogrammedchargecurrentmatchesthe 1Crateoftargetedbatterypacks.Themaximumfastcharge periodisdeterminedbythefollowingequation: SometypicaltimingvaluesaredetailedinTable3.RTIMER shouldnotbelessthan15k.Theactualtimelimitsused bytheLTC4011havearesolutionofapproximately30 secondsinadditiontothetolerancesgiventheElectrical Characteristicstable.Ifthetimerendswithoutavalid-Vor T/tchargetermination,thechargerentersthefaultstate. Themaximumtimeperiodisapproximately4.3hours. CellVoltageNetworkDesign An external resistor network is required to provide the averagesingle-cellvoltagetotheVCELLpinoftheLTC4011.
ThepropercircuitformulticellpacksisshowninFigure3. TheratioofR2toR1shouldbeafactorof(n-1),where nisthenumberofseriescellsinthebatterypack.The valueofR1shouldbebetween1kand100k.Thisrange limitsthesensingerrorcausedbyVCELLleakagecurrent andpreventstheONresistanceoftheinternalNFETbetweenVCDIVandGNDfromcausingasignificanterrorin theVCELLvoltage.Theexternalresistornetworkisalso usedtodetectbatteryinsertionandremoval.Thefilter formedbyC1andtheparallelcombinationofR1andR2
FOR TWO OR MORE SERIES CELLS BAT 12 LTC4011 VCELL VCDIV 8 R1 9 R2 = R1(n - 1) GND 5
4011 F03
R2
+
C1
Figure3.MulitpleCellVoltageDivider
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LTC4011 applicaTions inForMaTion
isrecommendedforrejectingPWMswitchingnoise.The valueofC1shouldbechosentoyielda1storderlowpass frequencyoflessthan500Hz.Inthecaseofasinglecell, theexternalapplicationcircuitshowninFigure4isrecommendedtoprovidethenecessarynoisefilteringand missingbatterydetection. ThermistorNetworkDesign The network for proper temperature sensing using a thermistorwithanegativetemperaturecoefficient(NTC) isshowninFigure5.R3isonlypresentforthermistors with an exponential temperature coefficient () above 3750. For thermistors with below 3750, replace R3 withashort.
12 9 8 BAT VCDIV VCELL 33nF
4011 F04
where: R0=thermistorresistance()atT0 T0=thermistorreferencetemperature(K) =exponentialtemperaturecoefficientofresistance Forthermistorswithlessthan3750,theequationforR3 yieldsanegativenumber.Thisnumbershouldbeusedto computeR2,eventhoughR3isreplacedwithashortinthe actualapplication.Anadditionalhightemperaturecharge qualificationerrorofbetween0Cand5Cmayoccurwhen usingthermistorswithlowerthan3750.Thermistors withnominallessthan3300shouldbeavoided. The filter formed by R4 and C1 in Figure 5 is optional but recommended for rejecting PWM switching noise. Alternatively,R4maybereplacedbyashort,andavalue chosenforC1whichwillprovideadequatefilteringfrom theTheveninimpedanceoftheremainingthermistornetwork.Thefilterpolefrequency,whichshouldbelessthan 500Hz,willvarymorewithbatterytemperaturewithout R4.Externalcomponentsshouldbechosentomakethe TheveninimpedancefromVTEMPtoGND100korless, includingR4,ifpresent. DisablingThermistorFunctions TemperaturesensingisoptionalinLTC4011applications. For low cost systems where temperature sensing may notberequired,theVTEMPpinmaysimplybewiredto VRTtodisabletemperaturequalificationofallcharging
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1 CELL 10k 10k
Figure4.Single-CellMonitorNetwork
VRT R1 R4 51k VTEMP C1 10nF
4011 F05
6 7
R3 RT
R2
Figure5.ExternalNTCThermistorNetwork
TheLTC4011isdesignedtoworkbestwitha5%10KNTC thermistorwithanear3750,suchastheSiemens/EPCOS B57620C103J062.Inthiscase,thevaluesfortheexternal networkaregivenby: R1=9.76k R2=28k R3=0 However,theLTC4011willoperatewithotherNTCthermistors having different nominal values or exponential temperaturecoefficients.Forthesethermistors,thedesign equationsfortheresistorsintheexternalnetworkare:
LTC4011 applicaTions inForMaTion
operations.However,thispracticeisnotrecommended forNiMHcellschargedwellaboveorbelowtheir1Crate, becausefastchargeterminationbasedsolelyonvoltage inflectionmaynotbeadequatetoprotectthebatteryfrom asevereovercharge.Aresistorbetween10kand20kmay beusedtoconnectVTEMPtoVRTifthepausefunctionis stilldesired. INTVDDRegulatorOutput IfBGATEisleftopen,theINTVDDpinoftheLTC4011can beusedasanadditionalsourceofregulatedvoltageinthe hostsystemanytimeREADYisactive.Switchingloads onINTVDDmayreducetheaccuracyofinternalanalog circuits used to monitor and terminate fast charging. Inaddition,DCcurrentdrawnfromtheINTVDDpincan greatlyincreaseinternalpowerdissipationatelevatedVCC voltages.Aminimumceramicbypasscapacitorof0.1F isrecommended. CalculatingAveragePowerDissipation TheusershouldensurethatthemaximumratedICjunction temperatureisnotexceededunderalloperatingconditions. The thermal resistance of the LTC4011 package (JA) is38C/W,providedtheexposedmetalpadisproperly solderedtothePCB.Theactualthermalresistanceinthe applicationwilldependontheamountofPCBcopperto whichthepackageissoldered.Feedthroughviasdirectly below the package that connect to inner copper layers arehelpfulinloweringthermalresistance.Thefollowing formulamaybeusedtoestimatethemaximumaverage power dissipation PD (in watts) of the LTC4011 under normaloperatingconditions. QBGATE=GatechargeofexternalN-channelMOSFET (ifused)incoulombs VLED=MaximumexternalLEDforwardvoltage RLED=ExternalLEDcurrent-limitingresistorusedin theapplication n=NumberofLEDsdrivenbytheLTC4011 SampleApplications Figures6through9detailsamplechargerapplications ofvariouscomplexities.CombinedwiththeTypicalApplicationonthefirstpageofthisdatasheet,theseFigures demonstrate some of the proper configurations of the LTC4011.MOSFETbodydiodesareshowninthesefigures strictlyforreferenceonly. Figure6showsaminimumapplication,whichmightbe encounteredinlowcostNiCdfastchargeapplications. FET-basedPowerPathcontrolallowsformaximuminput voltage range from the DC adapter. The LTC4011 uses -V to terminate the fast charge state, as no external temperature information is available. Nonsynchronous PWMswitchingisemployedtoreduceexternalcomponent cost.AsingleLEDindicateschargingstatus. A3ANiMHapplicationofmediumcomplexityisshownin Figure7.PowerPathcontrolthatiscompletelyFET-based allowsforbothminimuminputvoltageoverheadandminimumswitchoverlosswhenoperatingfromthebattery. P-channelMOSFETQ4functionsasaswitchtoconnectthe batterytothesystemloadwhenevertheDCinputadapter isremoved.Ifthemaximumbatteryvoltageislessthan themaximumratedVGSofQ4,diodeD1andresistorR5 are not required. Otherwise choose the Zener voltage ofD1tobelessthanthemaximumratedVGSofQ4.R5 providesabiascurrentof(VBAT-VZENER)/(R5+20k)for D1whentheinputadapterisremoved.ChooseR5tomake thiscurrent,whichisdrawnfromthebattery,justlarge enoughtodevelopthedesiredVGSacrossD1. Precharge,fastchargeandtop-offstatesareindicatedby externalLEDs.TheVTEMPthermistornetworkallowsthe LTC4011toaccuratelyterminatefastchargeunderavariety ofappliedchargerates.UseofasynchronousPWMtopologyimprovesefficiencyandlowerspowerdissipation.
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where: IDD=AverageexternalINTVDDloadcurrent,ifany IVRT=Loadcurrentdrawnbytheexternalthermistor networkfromVRT,ifany QTGATE=GatechargeofexternalP-channelMOSFET incoulombs
LTC4011 applicaTions inForMaTion
FROM ADAPTER 12V INFET FAULT CHRG TOC READY 10F
10H
10F
0.1F
Figure6.Minimum1ALTC4011Application
FROM ADAPTER 12V FAULT CHRG TOC READY
20F
4.7H
20F
0.1F
0.033F
0.068F
Figure7.3ANiMHChargerwithFullPowerPathControl
Afull-featured2ALTC4011applicationisshowninFigure8. FET-basedPowerPathallowsformaximuminputvoltage rangefromtheDCadapter.Theinherentvoltageratings oftheVCELL,VCDIV,SENSEandBATpinsallowcharging of one to sixteen series nickel cells in this application, governedonlybytheVCCoverheadlimitspreviouslydiscussed.Theapplicationincludesallaveragecellvoltage
andbatterytemperaturesensingcircuitryrequiredforthe LTC4011toutilizeitsfullrangeofchargequalification, safetymonitoringandfastchargeterminationfeatures. LED D1 indicates valid DC input voltage and installed battery,whileLEDsD2andD3indicatecharging.LEDD4 indicatesfaultconditions.ThegroundedCHEMpinselects theNiMHchargeterminationparameterset.
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LTC4011 applicaTions inForMaTion
While the LTC4011 is a complete, standalone solution, Figure9showsthatitcanalsobeinterfacedtoahost microprocessor.ThehostMCUcancontrolthecharger directlywithanopen-drainI/OportconnectedtotheVTEMP pin,ifthatportislowleakageandcantolerateatleast
FROM ADAPTER 12V INFET FAULT CHRG TOC READY 6.8H
2V.ThechargerstateismonitoredonthefourLTC4011 statusoutputs.ChargingofNiMHbatteriesisselectedin thisexample.However,NiCd(CHEMVRT)parameters couldbechosenaswell.
10F
D1
D2
D3
D4
10F
0.1F
Figure8.Full-Featured2ALTC4011Application
FROM ADAPTER 24V INFET FAULT CHRG TOC READY
10F
22H
0.1F PAUSE FROM MCU
NiMH PACK WITH 10k NTC (1Ahr)
Figure9.LTC4011withMCUInterface
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0
LTC4011 applicaTions inForMaTion
Unlikealloftheotherapplicationsdiscussedsofar,the batterycontinuestopowerthesystemduringcharging. TheMCUcouldbepowereddirectlyfromthebatteryor fromanytypeofpostregulatoroperatingfromthebattery. Inthisconfiguration,theLTC4011reliesexpresslyonthe abilityofthehostMCUtoknowwhenloadtransientswill beencountered.TheMCUshouldthenpausecharging (andthus-Vprocessing)duringthoseeventstoavoid prematurefastchargetermination.IftheMPUcannotreliablyperformthisfunction,fullPowerPathcontrolshould beimplemented.Inmostapplications,thereshouldnotbe anexternalloadonthebatteryduringcharge.Excessive batteryloadcurrentvariations,suchasthosegenerated byapost-regulatingPWM,cangeneratesufficientvoltage noisetocausetheLTC4011toprematurelyterminatea chargecycleand/orprematurelyrestartafastcharge.In thiscase,itmaybenecessarytoinhibittheLTC4011after charging is complete until external gas gauge circuitry indicatesthatrechargingisnecessary.Shutdownpower isappliedtotheLTC4011throughthebodydiodeofQ2 inthisapplication. Waveforms Sample waveforms for a standalone application during atypicalchargecycleareshowninFigure10.Notethat thesewaveformsarenottoscaleanddonotrepresentthe completerangeofpossibleactivity.Thefigureissimply intendedtoallowbetterconceptualunderstandingandto highlighttherelativebehaviorofcertainsignalsgenerated bytheLTC4011duringatypicalchargecycle. Initially, the LTC4011 is in low power shutdown as the 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.Figure10suggeststerminationbasedonT/t,whichforNiMHwould beanincreasegreaterthan1Cperminute. BecauseNiMHchargingterminatedduetoT/tandthe fastchargecyclehadlastedmorethantMAX/12minutes, the LTC4011 begins a top-off charge with a current of IPROG/10.Top-offisaninternallytimedchargeoftMAX/3 minutes with the CHRG and TOC outputs continuously asserted. Finally,theLTC4011enterstheautomaticrechargestate wheretheCHRGandTOCoutputsaredeasserted.The PWMisdisabledbutVCDIVremainsassertedtomonitor VCELL.Thechargetimerwillberesetandfastchargingwill resumeifVCELLdropsbelow1.325V.TheLTC4011enters shutdownwhentheDCadapterisremoved,minimizing currentdrawfromthebatteryintheabsenceofaninput powersource. WhilenotapartofthesamplewaveformsofFigure10, temperaturequalificationisanongoingpartofthechargingprocess,ifanexternalthermistornetworkisdetected bytheLTC4011.Shouldprescribedtemperaturelimitsbe exceededduringanyparticularchargingstate,charging wouldbesuspendeduntilthesensedtemperaturereturned toanacceptablerange. Battery-ControlledCharging BecauseoftheprogrammingarrangementoftheLTC4011, itmaybepossibletoconfigureitforbattery-controlled charging.Inthiscase,thebatterypackisdesignedto providecustomizedinformationtoanLTC4011-based charger,allowingasingledesigntoserviceawiderange ofapplicationbatteries.Assumethechargerisdesigned toprovideamaximumchargecurrentof800mA(RSENSE= 125m).Figure11showsa4-cellNiCdbatterypackfor which800mArepresentsa0.75Crate.Whenconnected tothecharger,thispackwouldprovidebatterytemperatureinformationandcorrectlyconfigurebothfastcharge terminationparametersandtimelimitsfortheinternal NiCdcells.
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LTC4011 applicaTions inForMaTion
READY
(PAUSE)
CHRG
TOC
Figure10.ChargingWaveformsExample
BATTERY PACK
TIMER 10
CHEM 4 NC
VTEMP 7 10k NTC
+
BATTERY PACK
CHEM 4
VTEMP 7
VCELL 8
+
R2
66.5k
1200mAhr NiCd CELLS
10k NTC
1500mAhr NiMH CELLS
-
4011 F11
-
4011 F12
Figure11.NiCdBatteryPackwithTimeLimitControl
Figure12.NiMHBatteryPackIndicatingNumberofCells
A second possibility is to configure an LTC4011-based chargertoacceptbatterypackswithvaryingnumbersof cells.ByincludingR2oftheaveragecellvoltagedivider networkshowninFigure3,battery-basedprogramming ofthenumberofseries-stackedcellscouldberealized withoutdefeatingLTC4011detectionofbatteryinsertion orremoval.Figure12showsa2-cellNiMHbatterypack thatprogramsthecorrectnumberofseriescellswhenitis connectedtothecharger,alongwithindicatingchemistry andprovidingtemperatureinformation. Anyofthesebatterypackchargecontrolconceptscouldbe combinedinavarietyofwaystoservicecustomapplication needs.Chargingparallelcellsisnotrecommended.
PCBLayoutConsiderations To prevent magnetic and electrical field radiation and highfrequencyresonantproblems,properlayoutofthe componentsconnectedtotheLTC4011isessential.Refer toFigure13.Formaximumefficiency,theswitchnode rise and fall times should be minimized. The following PCBdesignprioritylistwillhelpensurepropertopology. LayoutthePCBusingthisspecificorder. 1. Inputcapacitorsshouldbeplacedascloseaspossible toswitchingFETsupplyandgroundconnectionswith the shortest copper traces possible. The switching FETsmustbeonthesamelayerofcopperastheinput
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LTC4011 applicaTions inForMaTion
capacitors. Vias should not be used to make these connections. 2. Place the LTC4011 close to the switching FET gate terminals, keeping the connecting traces short to producecleandrivesignals.ThisrulealsoappliestoIC supplyandgroundpinsthatconnecttotheswitching FETsourcepins.TheICcanbeplacedontheopposite sideofthePCBfromtheswitchingFETs. 3. Placetheinductorinputascloseaspossibletothe drainoftheswitchingFETs.Minimizethesurfacearea oftheswitchnode.Makethetracewidththeminimum neededtosupporttheprogrammedchargecurrent. Usenocopperfillsorpours.Avoidrunningtheconnectiononmultiplecopperlayersinparallel.Minimize capacitancefromtheswitchnodetoanyothertrace orplane. 4. Placethechargecurrentsenseresistorimmediately adjacenttotheinductoroutput,andorientitsuchthat currentsensetracestotheLTC4011areshort.These feedbacktracesneedtoberuntogetherasasinglepair withthesmallestspacingpossibleonanygivenlayer onwhichtheyarerouted.Locateanyfiltercomponent onthesetracesnexttotheLTC4011,andnotatthe senseresistorlocation. 5. Placeoutputcapacitorsadjacenttothesenseresisitor outputandground. 6. Outputcapacitorgroundconnectionsmustfeedinto thesamecopperthatconnectstotheinputcapacitor groundbeforetyingbackintosystemground.
SWITCH NODE L1 VBAT HIGH FREQUENCY CIRCULATING PATH
DIRECTION OF CHARGING CURRENT
7. Connection of switching ground to system ground, oranyinternalgroundplaneshouldbesingle-point. Ifthesystemhasaninternalsystemgroundplane,a goodwaytodothisistoclusterviasintoasinglestar pointtomaketheconnection. 8. RouteanaloggroundasatracetiedbacktotheLTC4011 GNDpinbeforeconnectingtoanyotherground.Avoid usingthesystemgroundplane.AusefulCADtechnique istomakeanaloggroundaseparategroundnetand usea0resistortoconnectanaloggroundtosystem ground. 9. Agoodruleofthumbforviacountinagivenhigh currentpathistouse0.5Apervia.Beconsistentwhen applyingthisrule. 10.Ifpossible,placeallthepartslistedaboveonthesame PCBlayer. 11.CopperfillsorpoursaregoodforallpowerconnectionsexceptasnotedaboveinRule3.Copperplanes onmultiplelayerscanalsobeusedinparallel.This helpswiththermalmanagementandlowerstraceinductance,whichfurtherimprovesEMIperformance. 12.For best current programming accuracy, provide a Kelvin connection from RSENSE to SENSE and BAT. SeeFigure14foranexample. 13.Itisimportanttominimizeparasiticcapacitanceonthe TIMER,SENSEandBATpins.Thetracesconnecting thesepinstotheirrespectiveresistorsshouldbeas shortaspossible.
VIN
CIN
D1
COUT
BAT
RSENSE
4011 F14
SWITCHING GROUND
4011 F13
SENSE
BAT
Figure13.HighSpeedSwitchingPath
Figure14.KelvinSensingofChargeCurrent
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LTC4011 package DescripTion
FEPackage 20-LeadPlasticTSSOP(4.4mm)
(ReferenceLTCDWG#05-08-1663)
ExposedPadVariationCB
3.86 (.152) 6.40 - 6.60* (.252 - .260) 3.86 (.152) 20 1918 17 16 15 14 13 12 11
6.60 0.10 4.50 0.10
SEE NOTE 4
2.74 (.108) 0.45 0.05 1.05 0.10 0.65 BSC
6.40 2.74 (.252) (.108) BSC
RECOMMENDED SOLDER PAD LAYOUT
1 2 3 4 5 6 7 8 9 10 1.20 (.047) MAX
0 - 8
4.30 - 4.50* (.169 - .177)
0.25 REF
0.09 - 0.20 (.0035 - .0079)
0.50 - 0.75 (.020 - .030)
0.65 (.0256) BSC
NOTE: 1. CONTROLLING DIMENSION: MILLIMETERS MILLIMETERS 2. DIMENSIONS ARE IN (INCHES) 3. DRAWING NOT TO SCALE
0.195 - 0.30 (.0077 - .0118) TYP
0.05 - 0.15 (.002 - .006)
FE20 (CB) TSSOP 0204
4. RECOMMENDED MINIMUM PCB METAL SIZE FOR EXPOSED PAD ATTACHMENT *DIMENSIONS DO NOT INCLUDE MOLD FLASH. MOLD FLASH SHALL NOT EXCEED 0.150mm (.006") PER SIDE
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LTC4011 revision hisTory
REV B DATE 01/10 DESCRIPTION ChangestoTypicalApplication UpdatedOrderInformationSection ChangestoElectricalCharacteristics ChangestoOperationSection ChangestoApplicationsInformation ChangestoFigures6,7,8,9
(RevisionhistorybeginsatRevB)
PAGENUMBER 1 2 2,3,4 12,13,14 15,16,19, 21,22 19,20
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Information furnished by Linear Technology Corporation is believed to be accurate and reliable. However,noresponsibilityisassumedforitsuse.LinearTechnologyCorporationmakesnorepresentationthattheinterconnectionofitscircuitsasdescribedhereinwillnotinfringeonexistingpatentrights.
LTC4011 relaTeD parTs
PARTNUMBER LT 1510
(R)
DESCRIPTION Constant-Voltage/Constant-CurrentBatteryCharger 3AConstant-Voltage/Constant-CurrentBatteryCharger SEPICConstant-orProgrammable-Current/Constant- VoltageBatteryCharger SmartBatterySystemManager DualBatteryCharger/SelectorwithSPI HighEfficiency,ProgrammableVoltage/CurrentBattery Charger HighEfficiencyStandaloneNickelBatteryCharger StandaloneLinearNiMH/NiCdFastCharger SmartBatteryChargerController CoulombCounter/BatteryGasGauge 2.6ALowLossIdealDiode LowLossPowerPathControllers Dual2.6A,2.5Vto5.5V,IdealDiodes
COMMENTS Upto1.5AChargeCurrentforLi-Ion,NiCdandNiMHBatteries HighEfficiency,MinimumExternalComponentstoFastChargeLithium, NiMHandNiCdBatteries ChargerInputVoltageMaybeHigher,EqualtoorLowerthanBattery Voltage,500kHzSwitchingFrequency AutonomousPowerManagementandBatteryChargingforTwoSmart Batteries,SMBusRev1.1Compliant 11-BitV-DAC,0.8%VoltageAccuracy,10-BitI-DAC,5%CurrentAccuracy Constant-Current/Constant-VoltageSwitchingRegulator,ResistorVoltage/ CurrentProgramming,ACAdapterCurrentLimitandThermistorSensor andIndicatorOutputs CompleteNiMH/NiCdChargerinaSmall16-PinPackage,Constant-Current SwitchingRegulator CompleteNiMH/NiCdChargerinaSmallLeadedorLeadless16-Pin Package,NoSenseResistororBlockingDiodeRequired Level2ChargerOperateswithorwithoutMCUHost,SMBusRev.1.1 Compliant HighSideSenseofChargeQuantityandPolarityina10-PinMSOP NoExternalMOSFET,AutomaticSwitchingBetweenDCSources, Simplified,140mOnResistance,ThinSOTTMPackage VeryLowLossReplacementforPowerSupplyORingDiodesUsing MinimalExternalComponents,3VVIN28V,(3VVIN36VforHV) LowLossReplacementforORingDiodes,100mOnResistance
LT1511 LT1513 LTC1760 LTC1960 LTC4008
LTC4010 LTC4060 LTC4100 LTC4150 LTC4411 LTC4412/ LTC4412HV LTC4413
ThinSOTisatrademarkofLinearTechnologyCorporation.
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Linear Technology Corporation
(408)432-1900 FAX:(408)434-0507 www.linear.com
LT 0110 REV B * PRINTED IN USA
1630 McCarthy Blvd., Milpitas, CA 95035-7417
LINEAR TECHNOLOGY CORPORATION 2005

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