LP3876-ADJ资料

LP3876-ADJ3AFastUltraLowDropoutLinearRegulatorSeptember2003

LP3876-ADJ

3AFastUltraLowDropoutLinearRegulator

GeneralDescription

TheLP3876-ADJfastultralow-dropoutlinearregulatorsop-eratefroma+2.5Vto+7.0Vinputsupply.Theseultralowdropoutlinearregulatorsrespondveryquicklytostepchangesinload,whichmakesthemsuitableforlowvoltagemicroprocessorapplications.TheLP3876-ADJisdevelopedonaCMOSprocesswhichallowslowquiescentcurrentoperationindependentofoutputloadcurrent.ThisCMOSprocessalsoallowstheLP3876-ADJtooperateunderex-tremelylowdropoutconditions.

DropoutVoltage:Ultralowdropoutvoltage;typically80mVat300mAloadcurrentand800mVat3Aloadcurrent.GroundPinCurrent:Typically6mAat3Aloadcurrent.ShutdownMode:Typically1µAquiescentcurrentwhentheshutdownpinispulledlow.

AdjustableOutputVoltage:Theoutputvoltagemaybeprogrammedviatwoexternalresistors.

Features

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UltralowdropoutvoltageLowgroundpincurrentLoadregulationof0.08%

1µAquiescentcurrentinshutdownmodeGuaranteedoutputcurrentof3ADC

AvailableinTO-263andTO-220packagesMinimumoutputcapacitorrequirementsOvertemperature/overcurrentprotection

−40˚Cto+125˚Cjunctiontemperaturerange

Applications

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Microprocessorpowersupplies

GTL,GTL+,BTL,andSSTLbusterminatorsPowersuppliesforDSPsSCSIterminatorPostregulators

HighefficiencylinearregulatorsBatterychargers

Otherbatterypoweredapplications

TypicalApplicationCircuit

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*SeeApplicationHints

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LP3876-ADJConnectionDiagrams

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TopViewTO220-5PackageBent,StaggeredLeads

TopViewTO263-5Package

PinDescriptionforTO220-5andTO263-5Packages

Pin#12345

LP3876-ADJ

NameSDVINGNDVOUTADJ

ShutdownInputSupplyGroundOutputVoltageSetOutputVoltage

Function

OrderingInformation

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PackageTypeDesignatoris\"T\"forTO220package,and\"S\"forTO263package.

TABLE1.PackageMarkingandOrderingInformation

OutputVoltageADJADJADJ

OrderNumberLP3876ES-ADJLP3876ESX-ADJLP3876ET-ADJ

CurrentDescription

3A3A3A

PackageTypeTO263-5TO263-5TO220-5

PackageMarkingLP3876ES-ADJLP3876ES-ADJLP3876ET-ADJ

SuppliedAs:Rail

TapeandReelRail

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LP3876-ADJBlockDiagramLP3876-ADJ

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LP3876-ADJAbsoluteMaximumRatings

(Note1)

IOUT(Survival)

ShortCircuitProtected

IfMilitary/Aerospacespecifieddevicesarerequired,pleasecontacttheNationalSemiconductorSalesOffice/Distributorsforavailabilityandspecifications.StorageTemperatureRangeLeadTemperature(Soldering,5sec.)ESDRating(Note3)PowerDissipation(Note2)InputSupplyVoltage(Survival)ShutdownInputVoltage(Survival)

OutputVoltage(Survival),(Note6),(Note7)

260˚C2kV

InternallyLimited−0.3Vto+7.5V−0.3Vto7.5V−0.3Vto+6.0V−65˚Cto+150˚C

OperatingRatings

InputSupplyVoltage(Operating),(Note10)

ShutdownInputVoltage(Operating)

MaximumOperatingCurrent(DC)OperatingJunctionTemp.Range

2.5Vto7.0V−0.3Vto7.0V

3A

−40˚Cto+125˚C

ElectricalCharacteristicsLP3876-ADJ

LimitsinstandardtypefaceareforTJ=25˚C,andlimitsinboldfacetypeapplyoverthefulloperatingtemperaturerange.Unlessotherwisespecified:VIN=VO(NOM)+1.5V,IL=10mA,COUT=10µF,VSD=2V.Symbol

Parameter

Conditions

VOUT+1.5V≤VIN≤7V10mA≤IL≤3AVOUT+1.5V≤VIN≤7V10mA≤IL≤3AVOUT+1.5V≤VIN≤7.0V10mA≤IL≤3A

Typ(Note4)1.216100.020.060.080.14808005614.56

1051251000120091014151050

AA

LP3876-ADJ(Note5)Min1.1981.180

Max1.2341.253100

VnA%%Units

VADJIADJ∆VOL∆VO/∆IOUTAdjustPinVoltageAdjustPinInputCurrentOutputVoltageLineRegulation(Note8)OutputVoltageLoadRegulation(Note8)DropoutVoltage(Note9)

VIN-VOUTIL=300mAIL=3AIL=300mA

mV

IGNDGroundPinCurrentInNormalOperationModeGroundPinCurrentInShutdownModePeakOutputCurrentShortCircuitCurrent

IL=3AVSD≤0.3V-40˚C≤TJ≤85˚CVO≥VO(NOM)-4%

mA

IGNDIO(PK)ISCµA

SHORTCIRCUITPROTECTION

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LP3876-ADJElectricalCharacteristicsLP3876-ADJ(Continued)

LimitsinstandardtypefaceareforTJ=25˚C,andlimitsinboldfacetypeapplyoverthefulloperatingtemperaturerange.Unlessotherwisespecified:VIN=VO(NOM)+1.5V,IL=10mA,COUT=10µF,VSD=2V.Symbol

SHUTDOWNINPUT

VSDTTdOFFTdONISDShutdownThresholdTurn-offdelayTurn-ondelaySDInputCurrent

Output=HighOutput=LowIL=3AIL=3AVSD=VINVIN=VOUT+1VCOUT=10uF

VOUT=3.3V,f=120HzVIN=VOUT+0.5VCOUT=10uF

VOUT=3.3V,f=120Hzf=120Hz

BW=10Hz–100kHzVOUT=2.5V

BW=300Hz–300kHzVOUT=2.5V

VIN02025173

2

0.3

VµsµsnA

Parameter

Conditions

Typ(Note4)

LP3876-ADJ(Note5)Min

Max

Units

ACPARAMETERS

PSRRRippleRejection

57

dB

ρn(l/fOutputNoiseDensity0.8150100

µV

enOutputNoiseVoltageµV(rms)

Note1:Absolutemaximumratingsindicatelimitsbeyondwhichdamagetothedevicemayoccur.Operatingratingsindicateconditionsforwhichthedeviceisintendedtobefunctional,butdoesnotguaranteespecificperformancelimits.Forguaranteedspecificationsandtestconditions,seeElectricalCharacteristics.Theguaranteedspecificationsapplyonlyforthetestconditionslisted.Someperformancecharacteristicsmaydegradewhenthedeviceisnotoperatedunderthelistedtestconditions.

Note2:Atelevatedtemperatures,devicesmustbederatedbasedonpackagethermalresistance.ThedevicesinTO220packagemustbederatedatθjA=50˚C/W(with0.5in2,1oz.copperarea),junction-to-ambient(withnoheatsink).ThedevicesintheTO263surface-mountpackagemustbederatedatθjA=60˚C/W(with0.5in2,1oz.copperarea),junction-to-ambient.SeeApplicationHints.

Note3:Thehumanbodymodelisa100pFcapacitordischargedthrougha1.5kΩresistorintoeachpin.Note4:Typicalnumbersareat25˚Candrepresentthemostlikelyparametricnorm.Note5:Limitsareguaranteedbytesting,design,orstatisticalcorrelation.

Note6:Ifusedinadual-supplysystemwheretheregulatorloadisreturnedtoanegativesupply,theoutputmustbediode-clampedtoground.

Note7:TheoutputPMOSstructurecontainsadiodebetweentheVINandVOUTterminals.Thisdiodeisnormallyreversebiased.Thisdiodewillgetforwardbiasedifthevoltageattheoutputterminalisforcedtobehigherthanthevoltageattheinputterminal.Thisdiodecantypicallywithstand200mAofDCcurrentand1Ampofpeakcurrent.

Note8:Outputvoltagelineregulationisdefinedasthechangeinoutputvoltagefromthenominalvalueduetochangeintheinputlinevoltage.Outputvoltageloadregulationisdefinedasthechangeinoutputvoltagefromthenominalvalueduetochangeinloadcurrent.

Note9:Dropoutvoltageisdefinedastheminimuminputtooutputdifferentialvoltageatwhichtheoutputdrops2%belowthenominalvalue.Dropoutvoltagespecificationappliesonlytooutputvoltagesof2.5Vandabove.Foroutputvoltagesbelow2.5V,thedrop-outvoltageisnothingbuttheinputtooutputdifferential,sincetheminimuminputvoltageis2.5V.

Note10:TheminimumoperatingvalueforVINisequaltoeither[VOUT(NOM)+VDROPOUT]or2.5V,whicheverisgreater.

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LP3876-ADJTypicalPerformanceCharacteristics

CIN=10µF,S/DpinistiedtoVIN,VOUT=2.5V,VINDropoutVoltageVsOutputLoadCurrent

Unlessotherwisespecified:TJ=25˚C,COUT=10µF,

=VO(NOM)+1.5V,IL=10mA

GroundCurrentvsOutputLoadCurrent

VOUT=5V

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GroundCurrentvsOutputVoltage

IL=3A

ShutdownIQvsJunctionTemperature

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DCLoadReg.vsJunctionTemperatureDCLineRegulationvsTemperature

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LP3876-ADJTypicalPerformanceCharacteristicsUnlessotherwisespecified:TJ=25˚C,COUT=10µF,

CIN=10µF,S/DpinistiedtoVIN,VOUT=2.5V,VIN=VO(NOM)+1.5V,IL=10mA(Continued)

VINvsVOUTOverTemperature

NoisevsFrequency

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LoadTransientResponseCIN=COUT=10µF,OSCONLoadTransientResponseCIN=COUT=100µF,OSCON

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LoadTransientResponseCIN=COUT=100µF,POSCAPLoadTransientResponseCIN=COUT=10µF,TANTALUM

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LP3876-ADJTypicalPerformanceCharacteristicsUnlessotherwisespecified:TJ=25˚C,COUT=10µF,

CIN=10µF,S/DpinistiedtoVIN,VOUT=2.5V,VIN=VO(NOM)+1.5V,IL=10mA(Continued)

LoadTransientResponseCIN=COUT=100µF,TANTALUM

LoadTransientResponseCIN=COUT=10µF,OSCON

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LoadTransientResponseCIN=COUT=100µF,OSCONLoadTransientResponseCIN=COUT=100µF,POSCAP

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LoadTransientResponseCIN=COUT=10µF,TANTALUMLoadTransientResponseCIN=COUT=100µF,TANTALUM

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LP3876-ADJApplicationHints

VINRESTRICTIONSFORPROPERSTART-UP

Topreventmisoperation,ensurethatVINisbelow50mVbeforestart-upisinitiated.Thisscenariocanoccurinsys-temswithabackupbatteryusingreverse-biased\"blocking\"diodeswhichmayallowenoughleakagecurrenttoflowintotheVINnodetoraiseit’svoltageslightlyabovegroundwhenthemainpowerisremoved.UsinglowleakagediodesoraresistivepulldowncanpreventthevoltageatVINfromrisingabove50mV.LargebulkcapacitorsconnectedtoVINmayalsocauseastart-upproblemiftheydonotdischargefullybeforere-startisinitiated(butonlyifVINisallowedtofallbelow1V).Aresistorconnectedacrossthecapacitorwillallowittodischargemorequickly.Itshouldbenotedthattheprobabilityofa\"falsestart\"causedbyincorrectlogicstatesisextremelylow.

SETTINGTHEOUTPUTVOLTAGE

TheoutputvoltageissetusingtheresistorsR1andR2(seeTypicalApplicationCircuit).Theoutputisalsodependentonthereferencevoltage(typically1.216V)whichismeasuredattheADJpin.Theoutputvoltageisgivenbytheequation:

VOUT=VADJx(1+R1/R2)

ThisequationdoesnotincludeerrorsduetothebiascurrentflowingintheADJpinwhichistypicallyabout10nA.Thiserrortermisnegligibleformostapplications.IfR1is>100kΩ,asmallerrormaybeintroducedbytheADJbiascurrent.

Thetoleranceoftheexternalresistorsusedcontributesasignificanterrortotheoutputvoltageaccuracy,with1%resistorstypicallyaddingatotalerrorofapproximately1.4%totheoutputvoltage(thiserrorisinadditiontothetoleranceofthereferencevoltageatVADJ).

EXTERNALCAPACITORS

Likeanylow-dropoutregulator,externalcapacitorsarere-quiredtoassurestability.thesecapacitorsmustbecorrectlyselectedforproperperformance.

INPUTCAPACITOR:Aninputcapacitorofatleast1µFisrequired.CeramicorTantalummaybeused,andcapaci-tancemaybeincreasedwithoutlimit

OUTPUTCAPACITOR:Anoutputcapacitorisrequiredforloopstability.Itmustbelocatedlessthan1cmfromthedeviceandconnecteddirectlytotheoutputandgroundpinsusingtraceswhichhavenoothercurrentsflowingthroughthem(seePCBLayoutsection).

Theminimumvalueoftheoutputcapacitancethatcanbeusedforstablefull-loadoperationis10µF,butitmaybeincreasedwithoutlimit.TheoutputcapacitormusthaveanESRvalueasshowninthestableregionofthecurve(be-low).

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ESRCurve

CFF(FeedForwardCapacitor)

ThecapacitorCFFisrequiredtoaddphaseleadandhelpimproveloopcompensation.Thecorrectamountofcapaci-tancedependsonthevalueselectedforR1(seeTypicalApplicationCircuit).Thecapacitorshouldbeselectedsuchthatthezerofrequencyasgivenbytheequationshownbelowisapproximately45kHz:

Fz=45,000=1/(2xπxR1xCFF)

AgoodqualityceramicwithX5RorX7Rdielectricshouldbeusedforthiscapacitor.

SELECTINGACAPACITOR

Itisimportanttonotethatcapacitancetoleranceandvaria-tionwithtemperaturemustbetakenintoconsiderationwhenselectingacapacitorsothattheminimumrequiredamountofcapacitanceisprovidedoverthefulloperatingtempera-turerange.Ingeneral,agoodTantalumcapacitorwillshowverylittlecapacitancevariationwithtemperature,butace-ramicmaynotbeasgood(dependingondielectrictype).Aluminumelectrolyticsalsotypicallyhavelargetemperaturevariationofcapacitancevalue.

Equallyimportanttoconsiderisacapacitor’sESRchangewithtemperature:thisisnotanissuewithceramics,astheirESRisextremelylow.However,itisveryimportantinTan-talumandaluminumelectrolyticcapacitors.Bothshowin-creasingESRatcoldertemperatures,buttheincreaseinaluminumelectrolyticcapacitorsissoseveretheymaynotbefeasibleforsomeapplications(seeCapacitorCharacter-isticsSection).

CAPACITORCHARACTERISTICS

CERAMIC:Forvaluesofcapacitanceinthe10to100µFrange,ceramicsareusuallylargerandmorecostlythantantalumsbutgivesuperiorACperformanceforbypassinghighfrequencynoisebecauseofverylowESR(typicallylessthan10mΩ).However,somedielectrictypesdonothavegoodcapacitancecharacteristicsasafunctionofvoltageandtemperature.

Z5UandY5Vdielectricceramicshavecapacitancethatdropsseverelywithappliedvoltage.AtypicalZ5UorY5Vcapacitorcanlose60%ofitsratedcapacitancewithhalfoftheratedvoltageappliedtoit.TheZ5UandY5Valsoexhibit

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LP3876-ADJApplicationHints

(Continued)

aseveretemperatureeffect,losingmorethan50%ofnomi-nalcapacitanceathighandlowlimitsofthetemperaturerange.

X7RandX5Rdielectricceramiccapacitorsarestronglyrec-ommendedifceramicsareused,astheytypicallymaintainacapacitancerangewithin±20%ofnominaloverfulloperat-ingratingsoftemperatureandvoltage.Ofcourse,theyaretypicallylargerandmorecostlythanZ5U/Y5Utypesforagivenvoltageandcapacitance.

TANTALUM:SolidTantalumcapacitorsarerecommendedforuseontheoutputbecausetheirtypicalESRisveryclosetotheidealvaluerequiredforloopcompensation.TheyalsoworkwellasinputcapacitorsifselectedtomeettheESRrequirementspreviouslylisted.

Tantalumsalsohavegoodtemperaturestability:agoodqualityTantalumwilltypicallyshowacapacitancevaluethatvarieslessthan10-15%acrossthefulltemperaturerangeof125˚Cto−40˚C.ESRwillvaryonlyabout2Xgoingfromthehightolowtemperaturelimits.

TheincreasingESRatlowertemperaturescancauseoscil-lationswhenmarginalqualitycapacitorsareused(iftheESRofthecapacitorisneartheupperlimitofthestabilityrangeatroomtemperature).

ALUMINUM:Thiscapacitortypeoffersthemostcapaci-tanceforthemoney.Thedisadvantagesarethattheyarelargerinphysicalsize,notwidelyavailableinsurfacemount,andhavepoorACperformance(especiallyathigherfre-quencies)duetohigherESRandESL.

Comparedbysize,theESRofanaluminumelectrolyticishigherthaneitherTantalumorceramic,anditalsovariesgreatlywithtemperature.AtypicalaluminumelectrolyticcanexhibitanESRincreaseofasmuchas50Xwhengoingfrom25˚Cdownto−40˚C.

Itshouldalsobenotedthatmanyaluminumelectrolyticsonlyspecifyimpedanceatafrequencyof120Hz,whichindicatestheyhavepoorhighfrequencyperformance.Onlyaluminumelectrolyticsthathaveanimpedancespecifiedatahigherfrequency(between20kHzand100kHz)shouldbeusedfortheLP387X.Deratingmustbeappliedtothemanufacturer’sESRspecification,sinceitistypicallyonlyvalidatroomtemperature.

Anyapplicationsusingaluminumelectrolyticsshouldbethoroughlytestedatthelowestambientoperatingtempera-turewhereESRismaximum.

PCBLAYOUT

GoodPClayoutpracticesmustbeusedorinstabilitycanbeinducedbecauseofgroundloopsandvoltagedrops.Theinputandoutputcapacitorsmustbedirectlyconnectedtotheinput,output,andgroundpinsoftheLP387Xusingtraceswhichdonothaveothercurrentsflowinginthem(Kelvinconnect).

ThebestwaytodothisistolayoutCINandCOUTnearthedevicewithshorttracestotheVIN,VOUT,andgroundpins.Theregulatorgroundpinshouldbeconnectedtotheexter-nalcircuitgroundsothattheregulatoranditscapacitorshavea\"singlepointground\".

Itshouldbenotedthatstabilityproblemshavebeenseeninapplicationswhere\"vias\"toaninternalgroundplanewereusedatthegroundpointsoftheICandtheinputandoutputcapacitors.Thiswascausedbyvaryinggroundpotentialsat

thesenodesresultingfromcurrentflowingthroughthegroundplane.Usingasinglepointgroundtechniquefortheregulatorandit’scapacitorsfixedtheproblem.

SincehighcurrentflowsthroughthetracesgoingintoVINandcomingfromVOUT,Kelvinconnectthecapacitorleadstothesepinssothereisnovoltagedropinserieswiththeinputandoutputcapacitors.

RFI/EMISUSCEPTIBILITY

RFI(radiofrequencyinterference)andEMI(electromagneticinterference)candegradeanyintegratedcircuit’sperfor-mancebecauseofthesmalldimensionsofthegeometriesinsidethedevice.Inapplicationswherecircuitsourcesarepresentwhichgeneratesignalswithsignificanthighfre-quencyenergycontent(>1MHz),caremustbetakentoensurethatthisdoesnotaffecttheICregulator.

IfRFI/EMInoiseispresentontheinputsideoftheregulator(suchasapplicationswheretheinputsourcecomesfromtheoutputofaswitchingregulator),goodceramicbypassca-pacitorsmustbeusedattheinputpinoftheIC.

IfaloadisconnectedtotheICoutputwhichswitchesathighspeed(suchasaclock),thehigh-frequencycurrentpulsesrequiredbytheloadmustbesuppliedbythecapacitorsontheICoutput.Sincethebandwidthoftheregulatorloopislessthan100kHz,thecontrolcircuitrycannotrespondtoloadchangesabovethatfrequency.ThemeanstheeffectiveoutputimpedanceoftheICatfrequenciesabove100kHzisdeterminedonlybytheoutputcapacitor(s).

Inapplicationswheretheloadisswitchingathighspeed,theoutputoftheICmayneedRFisolationfromtheload.Itisrecommendedthatsomeinductancebeplacedbetweentheoutputcapacitorandtheload,andgoodRFbypasscapaci-torsbeplaceddirectlyacrosstheload.

PCBlayoutisalsocriticalinhighnoiseenvironments,sinceRFI/EMIiseasilyradiateddirectlyintoPCtraces.Noisycircuitryshouldbeisolatedfrom\"clean\"circuitswherepos-sible,andgroundedthroughaseparatepath.AtMHzfre-quencies,groundplanesbegintolookinductiveandRFI/EMIcancausegroundbounceacrossthegroundplane.Inmulti-layerPCBapplications,careshouldbetakeninlayoutsothatnoisypowerandgroundplanesdonotradiatedirectlyintoadjacentlayerswhichcarryanalogpowerandground.

OUTPUTNOISE

Noiseisspecifiedintwoways-SpotNoiseorOutputnoisedensityistheRMSsumofallnoisesources,measuredattheregulatoroutput,ataspe-cificfrequency(measuredwitha1Hzbandwidth).Thistypeofnoiseisusuallyplottedonacurveasafunctionoffre-quency.

TotaloutputNoiseorBroad-bandnoiseistheRMSsumofspotnoiseoveraspecifiedbandwidth,usuallyseveraldecadesoffrequencies.

Attentionshouldbepaidtotheunitsofmeasurement.SpotnoiseismeasuredinunitsµV/√HzornV/√HzandtotaloutputnoiseismeasuredinµV(rms).

Theprimarysourceofnoiseinlow-dropoutregulatorsistheinternalreference.InCMOSregulators,noisehasalowfrequencycomponentandahighfrequencycomponent,whichdependstronglyonthesiliconareaandquiescentcurrent.Noisecanbereducedintwoways:byincreasingthetransistorareaorbyincreasingthecurrentdrawnbytheinternalreference.Increasingtheareawilldecreasethechanceoffittingthedieintoasmallerpackage.Increasing

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LP3876-ADJApplicationHints

(Continued)

thecurrentdrawnbytheinternalreferenceincreasesthetotalsupplycurrent(groundpincurrent).Usinganoptimizedtrade-offofgroundpincurrentanddiesize,LP387Xachieveslownoiseperformanceandlowquiescentcurrentoperation.

ThetotaloutputnoisespecificationforLP387XispresentedintheElectricalCharacteristicstable.TheOutputnoiseden-sityatdifferentfrequenciesisrepresentedbyacurveundertypicalperformancecharacteristics.

SHORT-CIRCUITPROTECTION

TheLP3876-ADJisshortcircuitprotectedandintheeventofapeakover-currentcondition,theshort-circuitcontrolloopwillrapidlydrivetheoutputPMOSpasselementoff.Oncethepowerpasselementshutsdown,thecontrolloopwillrapidlycycletheoutputonandoffuntiltheaveragepowerdissipationcausesthethermalshutdowncircuittorespondtoservotheon/offcyclingtoalowerfrequency.Pleaserefertothesectiononthermalinformationforpowerdissipationcalculations.

SHUTDOWNOPERATION

ACMOSLogiclevelsignalattheshutdown(SD)pinwillturn-offtheregulator.PinSDmustbeactivelyterminatedthrougha10kΩpull-upresistorforaproperoperation.Ifthispinisdrivenfromasourcethatactivelypullshighandlow(suchasaCMOSrailtorailcomparator),thepull-upresistorisnotrequired.ThispinmustbetiedtoVinifnotused.DROPOUTVOLTAGE

Thedropoutvoltageofaregulatorisdefinedastheminimuminput-to-outputdifferentialrequiredtostaywithin2%ofthenominaloutputvoltage.ForCMOSLDOs,thedropoutvolt-ageistheproductoftheloadcurrentandtheRds(on)oftheinternalMOSFET.

REVERSECURRENTPATH

TheinternalMOSFETinLP3876-ADJhasaninherentpara-siticdiode.Duringnormaloperation,theinputvoltageishigherthantheoutputvoltageandtheparasiticdiodeisreversebiased.However,iftheoutputispulledabovetheinputinanapplication,thencurrentflowsfromtheoutputtotheinputastheparasiticdiodegetsforwardbiased.Theoutputcanbepulledabovetheinputaslongasthecurrentintheparasiticdiodeislimitedto200mAcontinuousand1Apeak.

POWERDISSIPATION/HEATSINKING

TheLP3876-ADJcandeliveracontinuouscurrentof3Aoverthefulloperatingtemperaturerange.Aheatsinkmayberequireddependingonthemaximumpowerdissipationandmaximumambienttemperatureoftheapplication.Underallpossibleconditions,thejunctiontemperaturemustbewithintherangespecifiedunderoperatingconditions.Thetotalpowerdissipationofthedeviceisgivenby:PD=(VIN−VOUT)IOUT+(VIN)IGNDwhereIGNDistheoperatinggroundcurrentofthedevice(specifiedunderElectricalCharacteristics).

Themaximumallowabletemperaturerise(TRmax)dependsonthemaximumambienttemperature(TAmax)oftheappli-cation,andthemaximumallowablejunctiontemperature(TJmax):

TRmax=TJmax−TAmax11

ThemaximumallowablevalueforjunctiontoambientTher-malResistance,θJA,canbecalculatedusingtheformula:θJA=TRmax/PDTheLP3876-ADJisavailableinTO-220andTO-263pack-ages.Thethermalresistancedependsonamountofcopperareaorheatsink,andonairflow.IfthemaximumallowablevalueofθJAcalculatedaboveis≥60˚C/WforTO-220packageand≥60˚C/WforTO-263packagenoheatsinkisneededsincethepackagecandissipateenoughheattosatisfytheserequirements.IfthevalueforallowableθJAfallsbelowtheselimits,aheatsinkisrequired.

HEATSINKINGTO-220PACKAGE

ThethermalresistanceofaTO220packagecanbereducedbyattachingittoaheatsinkoracopperplaneonaPCboard.Ifacopperplaneistobeused,thevaluesofθJAwillbesameasshowninnextsectionforTO263package.

Theheatsinktobeusedintheapplicationshouldhaveaheatsinktoambientthermalresistance,θHA≤θJA−θCH−θJC.

Inthisequation,θCHisthethermalresistancefromthecasetothesurfaceoftheheatsinkandθJCisthethermalresis-tancefromthejunctiontothesurfaceofthecase.θJCisabout3˚C/WforaTO220package.ThevalueforθCHde-pendsonmethodofattachment,insulator,etc.θCHvariesbetween1.5˚C/Wto2.5˚C/W.Iftheexactvalueisunknown,2˚C/Wcanbeassumed.

HEATSINKINGTO-263PACKAGE

TheTO-263packageusesthecopperplaneonthePCBasaheatsink.Thetabofthesepackagesaresolderedtothecopperplaneforheatsinking.Figure1showsacurvefortheθJAofTO-263packagefordifferentcopperareasizes,usingatypicalPCBwith1ouncecopperandnosoldermaskoverthecopperareaforheatsinking.

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FIGURE1.θJAvsCopper(1Ounce)AreaforTO-263

packageAsshowninthefigure,increasingthecopperareabeyond1squareinchproducesverylittleimprovement.TheminimumvalueforθJAfortheTO-263packagemountedtoaPCBis32˚C/W.

Figure2showsthemaximumallowablepowerdissipationforTO-263packagesfordifferentambienttemperatures,assumingθJAis35˚C/Wandthemaximumjunctiontempera-tureis125˚C.

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LP3876-ADJApplicationHints

(Continued)

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FIGURE2.Maximumpowerdissipationvsambient

temperatureforTO-263package

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LP3876-ADJPhysicalDimensions

unlessotherwisenoted

inches(millimeters)

TO2205-lead,Molded,StaggerBendPackage(TO220-5)

NSPackageNumberT05D

ForOrderNumbers,refertothe“OrderingInformation”sectionofthisdocument.

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LP3876-ADJ3AFastUltraLowDropoutLinearRegulatorPhysicalDimensions

inches(millimeters)unlessotherwisenoted(Continued)

TO2635-Lead,Molded,SurfaceMountPackage(TO263-5)

NSPackageNumberTS5B

ForOrderNumbers,refertothe“OrderingInformation”sectionofthisdocument.

LIFESUPPORTPOLICY

NATIONAL’SPRODUCTSARENOTAUTHORIZEDFORUSEASCRITICALCOMPONENTSINLIFESUPPORTDEVICESORSYSTEMSWITHOUTTHEEXPRESSWRITTENAPPROVALOFTHEPRESIDENTANDGENERALCOUNSELOFNATIONALSEMICONDUCTORCORPORATION.Asusedherein:1.Lifesupportdevicesorsystemsaredevicesorsystemswhich,(a)areintendedforsurgicalimplantintothebody,or(b)supportorsustainlife,andwhosefailuretoperformwhenproperlyusedinaccordancewithinstructionsforuseprovidedinthelabeling,canbereasonablyexpectedtoresultinasignificantinjurytotheuser.

NationalSemiconductorAmericasCustomerSupportCenter

Email:new.feedback@nsc.comTel:1-800-272-9959

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2.Acriticalcomponentisanycomponentofalifesupportdeviceorsystemwhosefailuretoperformcanbereasonablyexpectedtocausethefailureofthelifesupportdeviceorsystem,ortoaffectitssafetyoreffectiveness.

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Nationaldoesnotassumeanyresponsibilityforuseofanycircuitrydescribed,nocircuitpatentlicensesareimpliedandNationalreservestherightatanytimewithoutnoticetochangesaidcircuitryandspecifications.