LM138

LM138/LM338

5-AmpAdjustableRegulators

GeneralDescription

TheLM138seriesofadjustable3-terminalpositivevoltageregulatorsiscapableofsupplyinginexcessof5Aovera1.2Vto32Voutputrange.Theyareexceptionallyeasytouseandrequireonly2resistorstosettheoutputvoltage.Carefulcircuitdesignhasresultedinoutstandingloadandlineregulation—comparabletomanycommercialpowersupplies.TheLM138familyissuppliedinastandard3-leadtransistorpackage.

AuniquefeatureoftheLM138familyistime-dependentcur-rentlimiting.Thecurrentlimitcircuitryallowspeakcurrentsofupto12Atobedrawnfromtheregulatorforshortperiodsoftime.ThisallowstheLM138tobeusedwithheavytran-sientloadsandspeedsstart-upunderfull-loadconditions.Undersustainedloadingconditions,thecurrentlimitde-creasestoasafevalueprotectingtheregulator.Alsoin-cludedonthechiparethermaloverloadprotectionandsafeareaprotectionforthepowertransistor.Overloadprotectionremainsfunctionaleveniftheadjustmentpinisaccidentallydisconnected.

Normally,nocapacitorsareneededunlessthedeviceissitu-atedmorethan6inchesfromtheinputfiltercapacitorsinwhichcaseaninputbypassisneeded.Anoutputcapacitorcanbeaddedtoimprovetransientresponse,whilebypass-ingtheadjustmentpinwillincreasetheregulator’sripplere-jection.

Besidesreplacingfixedregulatorsordiscretedesigns,theLM138isusefulinawidevarietyofotherapplications.Sincetheregulatoris“floating”andseesonlytheinput-to-outputdifferentialvoltage,suppliesofseveralhundredvoltscanberegulatedaslongasthemaximuminputtooutputdifferentialisnotexceeded,i.e.,donotshort-circuitoutputtoground.ThepartnumbersintheLM138serieswhichhaveaKsuffixarepackagedinastandardSteelTO-3package,whilethosewithaTsuffixarepackagedinaTO-220plasticpackage.TheLM138isratedfor−55˚C≤TJ≤+150˚C,andtheLM338isratedfor0˚C≤TJ≤+125˚C.

Features

nnnnnnn

Guaranteed7ApeakoutputcurrentGuaranteed5AoutputcurrentAdjustableoutputdownto1.2VGuaranteedthermalregulation

CurrentlimitconstantwithtemperatureP+ProductEnhancementtestedOutputisshort-circuitprotected

Applications

nAdjustablepowersuppliesnConstantcurrentregulatorsnBatterychargers

ConnectionDiagrams

(SeePhysicalDimensionsectionforfurtherinformation)

(TO-220)PlasticPackage

(TO-3STEEL)MetalCanPackage

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FrontView

OrderNumberLM338TSeeNSPackageNumberT03B

BottomView

OrderNumberLM138KSTEELorLM338KSTEEL

SeeNSPackageNumberK02A

©1999NationalSemiconductorCorporationDS009060www.national.com

AbsoluteMaximumRatings(Note1)

IfMilitary/Aerospacespecifieddevicesarerequired,pleasecontacttheNationalSemiconductorSalesOffice/Distributorsforavailabilityandspecifications.(Note4)

PowerDissipation

Input/OutputVoltageDifferentialStorageTemperature

Internallylimited

+40V,−0.3V−65˚Cto+150˚C

LeadTemperature

MetalPackage(Soldering,10seconds)PlasticPackage(Soldering,4seconds)ESDTolerance

300˚C260˚CTBD

OperatingTemperatureRange

LM138LM338

−55˚C≤TJ≤+150˚C0˚C≤TJ≤+125˚C

ElectricalCharacteristics

SpecificationswithstandardtypefaceareforTJ=25˚C,andthosewithboldfacetypeapplyoverfullOperatingTempera-tureRange.Unlessotherwisespecified,VIN−VOUT=5V;andIOUT=10mA.(Note2)SymbolVREFVRLINEVRLOADParameter

ReferenceVoltageLineRegulationLoadRegulationThermalRegulation

IADJ∆IADJ∆VR/TILOAD(Min)ICLAdjustmentPinCurrentAdjustmentPinCurrentChangeTemperatureStabilityMinimumLoadCurrentCurrentLimit

10mA≤IOUT≤5A,3V≤(VIN−VOUT)≤35VTMIN≤TJ≤TMAXVIN−VOUT=35VVIN−VOUT≤10VDC

0.5msPeakVIN−VOUT=30V

VNRMSOutputNoise,%ofVOUT10Hz≤f≤10kHz

57

81210.003

1

AAA%

13.5

5

%mA

Conditions

Min

3V≤(VIN−VOUT)≤35V,10mA≤IOUT≤5A,P≤50W3V≤(VIN−VOUT)≤35V(Note3)10mA≤IOUT≤5A(Note3)20msPulse

0.0050.020.10.30.002450.2

0.010.040.30.60.011005

%/V%/V%%%/WµAµA

1.19

LM138Typ1.24

Max1.29

VUnits

ElectricalCharacteristics

Symbol∆VR/TILOAD(Min)ICLParameter

TemperatureStabilityMinimumLoadCurrentCurrentLimit

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Conditions

Min

TMIN≤TJ≤TMAXVIN−VOUT=35VVIN−VOUT≤10VDC

0.5msPeakVIN−VOUT=30V

57

812

1

0.003

AAA%

LM338Typ13.5

10Max

%mAUnits

VNRMSOutputNoise,%ofVOUT10Hz≤f≤10kHz

TypicalPerformanceCharacteristics

TemperatureStability

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MinimumOperatingCurrent

OutputImpedance

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RippleRejectionRippleRejectionRippleRejection

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LineTransientResponseLoadTransientResponse

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ApplicationHints

Inoperation,theLM138developsanominal1.25Vreferencevoltage,VREF,betweentheoutputandadjustmentterminal.ThereferencevoltageisimpressedacrossprogramresistorR1and,sincethevoltageisconstant,aconstantcurrentI1thenflowsthroughtheoutputsetresistorR2,givinganout-putvoltageof

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ApplicationHints

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LoadRegulation

TheLM138iscapableofprovidingextremelygoodloadregulationbutafewprecautionsareneededtoobtainmaxi-mumperformance.Thecurrentsetresistorconnectedbe-tweentheadjustmentterminalandtheoutputterminal(usu-ally240Ω)shouldbetieddirectlytotheoutputoftheregulator(case)ratherthanneartheload.Thiseliminateslinedropsfromappearingeffectivelyinserieswiththerefer-enceanddegradingregulation.Forexample,a15Vregula-torwith0.05Ωresistancebetweentheregulatorandloadwillhavealoadregulationduetolineresistanceof0.05ΩxIL.Ifthesetresistorisconnectedneartheloadtheeffectivelineresistancewillbe0.05Ω(1+R2/R1)orinthiscase,11.5timesworse.

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Figure2showstheeffectofresistancebetweentheregula-torand240Ωsetresistor.

FIGURE1.

Sincethe50µAcurrentfromtheadjustmentterminalrepre-sentsanerrorterm,theLM138wasdesignedtominimizeIADJandmakeitveryconstantwithlineandloadchanges.Todothis,allquiescentoperatingcurrentisreturnedtotheoutputestablishingaminimumloadcurrentrequirement.Ifthereisinsufficientloadontheoutput,theoutputwillrise.ExternalCapacitors

Aninputbypasscapacitorisrecommended.A0.1µFdiscor1µFsolidtantalumontheinputissuitableinputbypassingforalmostallapplications.Thedeviceismoresensitivetotheabsenceofinputbypassiingwhenadjustmentoroutputcapacitorsareusedbuttheabovevalueswilleliminatethepossiblityofproblems.

TheadjustmentterminalcanbebypassedtogroundontheLM138toimproveripplerejection.Thisbypasscapacitorpreventsripplefrombeingamplifiedastheoutputvoltageisincreased.Witha10µFbypasscapacitor75dBripplerejec-tionisobtainableatanyoutputlevel.Increasesover20µFdonotappreciablyimprovetheripplerejectionatfrequen-ciesabove120Hz.Ifthebypasscapacitorisused,itissometimesnecessarytoincludeprotectiondiodestopreventthecapacitorfromdischargingthroughinternallowcurrentpathsanddamagingthedevice.

Ingeneral,thebesttypeofcapacitorstousearesolidtanta-lum.Solidtantalumcapacitorshavelowimpedanceevenathighfrequencies.Dependinguponcapacitorconstruction,ittakesabout25µFinaluminumelectrolytictoequal1µFsolidtantalumathighfrequencies.Ceramiccapacitorsarealsogoodathighfrequencies;butsometypeshavealargedecreaseincapacitanceatfrequenciesaround0.5MHz.Forthisreason,0.01µFdiscmayseemtoworkbetterthana0.1µFdiscasabypass.

AlthoughtheLM138isstablewithnooutputcapacitors,likeanyfeedbackcircuit,certainvaluesofexternalcapacitancecancauseexcessiveringing.Thisoccurswithvaluesbe-tween500pFand5000pF.A1µFsolidtantalum(or25µFaluminumelectrolytic)ontheoutputswampsthiseffectandinsuresstability.

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FIGURE2.RegulatorwithLineResistanceinOutputLead

WiththeTO-3package,itiseasytominimizetheresistancefromthecasetothesetresistor,byusing2separateleadstothecase.ThegroundofR2canbereturnednearthegroundoftheloadtoprovideremotegroundsensingandimproveloadregulation.

ProtectionDiodes

WhenexternalcapacitorsareusedwithanyICregulatoritissometimesnecessarytoaddprotectiondiodestopreventthecapacitorsfromdischargingthroughlowcurrentpointsintotheregulator.Most20µFcapacitorshavelowenoughinternalseriesresistancetodeliver20Aspikeswhenshorted.Althoughthesurgeisshort,thereisenoughenergytodamagepartsoftheIC.

Whenanoutputcapacitorisconnectedtoaregulatorandtheinputisshorted,theoutputcapacitorwilldischargeintotheoutputoftheregulator.Thedischargecurrentdependsonthevalueofthecapacitor,theoutputvoltageoftheregu-lator,andtherateofdecreaseofVIN.IntheLM138thisdis-chargepathisthroughalargejunctionthatisabletosustain25Asurgewithnoproblem.Thisisnottrueofothertypesofpositiveregulators.Foroutputcapacitorsof100µForlessatoutputof15Vorless,thereisnoneedtousediodes.

Thebypasscapacitorontheadjustmentterminalcandis-chargethroughalowcurrentjunction.Dischargeoccurswheneithertheinputoroutputisshorted.InternaltotheLM138isa50Ωresistorwhichlimitsthepeakdischargecur-rent.Noprotectionisneededforoutputvoltagesof25Vorlessand10µFcapacitance.Figure3showsanLM138withprotectiondiodesincludedforusewithoutputsgreaterthan25Vandhighvaluesofoutputcapacitance.

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ApplicationHints

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D1protectsagainstC1D2protectsagainstC2

FIGURE3.RegulatorwithProtectionDiodes

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TypicalApplications

RegulatorandVoltageReference

1.2V–25VAdjustableRegulator

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TemperatureController

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Fulloutputcurrentnotavailableathighinput-outputvoltages

†Optional—improvestransientresponse.Outputcapacitorsintherangeof1µFto1000µFofaluminumortantalumelectrolyticarecommonlyusedtoprovideimprovedoutputimpedanceandrejectionoftransients.*Neededifdeviceismorethan6inchesfromfiltercapacitors.

**R1=240ΩforLM138.R1,R2asanassemblycanbeorderedfromBourns:

MILpartno.7105A-AT2-502COMMpartno.7105A-AT7-502

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SchematicDiagram

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TypicalApplications

PrecisionPowerRegulatorwithLowTemperatureCoefficient

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*Adjustfor3.75acrossR1

SlowTurn-On15VRegulatorAdjustableRegulatorwithImprovedRippleRejection

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†Solidtantalum

*DischargesC1ifoutputisshortedtoground**R1=240ΩforLM138

HighStability10VRegulatorDigitallySelectedOutputs

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*SetsmaximumVOUT**R1=240ΩforLM138

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TypicalApplications

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15ARegulator

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*Minimumload—100mA

5VLogicRegulatorwithElectronicShutdown**LightController

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**Minimumoutput≈1.2V

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TypicalApplications

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0to22VRegulator

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*R1=240Ω,R2=5kforLM138Fulloutputcurrentnotavailableathighinput-outputvoltages

12VBatteryCharger

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TypicalApplications

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PrecisionCurrentLimiter

AdjustableCurrentRegulator

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5ACurrentRegulatorTrackingPreregulator

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AdjustingMultipleOn-CardRegulatorswithSingleControl*

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†Minimumload—10mA*Alloutputswithin±100mV

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TypicalApplications

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PowerAmplifier

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AV=1,RF=10k,CF=100pFAV=10,RF=100k,CF=10pFBandwidth≥100kHzDistortion≤0.1%

Simple12VBatteryCharger

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UseofRSallowslowchargingrateswithfullychargedbattery.**The1000µFisrecommendedtofilteroutinputtransients

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TypicalApplications

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Adjustable15ARegulator

CurrentLimited6VCharger

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*Setmaxchargecurrentto3A

**THE1000µFisrecommendedtofilteroutinputtransients.

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10ARegulator

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*Minimumload—100mA

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PhysicalDimensions

inches(millimeters)unlessotherwisenoted

2LeadTO-3MetalCanPackage(K)OrderNumberLM138KorLM338KSTEEL

NSPackageNumberK02A

3LeadMoldedTO-220(T)OrderNumberLM338TNSPackageNumberT03B

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LM138/LM3385-AmpAdjustableRegulatorsLIFESUPPORTPOLICY

NATIONAL’SPRODUCTSARENOTAUTHORIZEDFORUSEASCRITICALCOMPONENTSINLIFESUPPORTDE-VICESORSYSTEMSWITHOUTTHEEXPRESSWRITTENAPPROVALOFTHEPRESIDENTOFNATIONALSEMI-CONDUCTORCORPORATION.Asusedherein:

2.Acriticalcomponentisanycomponentofalifesupport1.Lifesupportdevicesorsystemsaredevicesorsys-deviceorsystemwhosefailuretoperformcanberea-temswhich,(a)areintendedforsurgicalimplantinto

sonablyexpectedtocausethefailureofthelifesupportthebody,or(b)supportorsustainlife,andwhosefail-deviceorsystem,ortoaffectitssafetyoreffectiveness.uretoperformwhenproperlyusedinaccordance

withinstructionsforuseprovidedinthelabeling,canbereasonablyexpectedtoresultinasignificantinjurytotheuser.

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