LM4871MNOPB,LM4871MMNOPB,LM4871MMNOPB,LM4871MMNOPB,,LM4871MXNOPB, 规格书,Datasheet 资料

LM4871 3W Audio Power Amplifier with Shutdown Mode

Literature Number: SNAS002E

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LM48713WAudioPowerAmplifierwithShutdownModeJanuary2003

LM4871

3WAudioPowerAmplifierwithShutdownMode

GeneralDescription

TheLM4871isamonobridgedaudiopoweramplifierca-pableofdelivering3Wofcontinuousaveragepowerintoa3Ωloadwithlessthan10%THDwhenpoweredbya5Vpowersupply(Note1).Toconservepowerinportableappli-cations,theLM4871’smicropowershutdownmode(IQ=0.6µA,typ)isactivatedwhenVDDisappliedtotheSHUT-DOWNpin.

Boomeraudiopoweramplifiersaredesignedspecificallytoprovidehighpower,highfidelityaudiooutput.Theyrequirefewexternalcomponentsandoperateonlowsupplyvolt-agesfrom2.0Vto5.5V.SincetheLM4871doesnotrequireoutputcouplingcapacitors,bootstrapcapacitors,orsnubbernetworks,itisideallysuitedforlow-powerportablesystemsthatrequireminimumvolumeandweight.

AdditionalLM4871featuresincludethermalshutdownpro-tection,unity-gainstability,andexternalgainset.

Note1:AnLM4871LDthathasbeenproperlymountedtoacircuitboardwilldeliver3Winto3Ω(at10%THD).TheotherpackageoptionsfortheLM4871willdeliver1.5Winto8Ω(at10%THD).SeetheApplicationInformationsectionsforfurtherinformationconcerningtheLM4871LD,LM4871MM,LM4871M,andtheLM4871N.

KeySpecifications

nnnnnn

POat10%THD+N,1kHzLM4871LD:3Ω,4Ωloads3W(typ),2.5W(typ)AllotherLM4871packages:8Ωload1.5W(typ)Shutdowncurrent0.6µA(typ)Supplyvoltagerange2.0Vto5.5VTHDat1kHzat1Wcontinuousaverageoutputpowerinto8Ω0.5%(max)

Features

nNooutputcouplingcapacitors,bootstrapcapacitors,orsnubbercircuitsrequirednUnity-gainstable

nLLP,MSOP,SO,orDIPpackagingnExternalgainconfigurationcapabilitynPincompatiblewiththeLM4861

Applications

nPortablecomputersnDesktopcomputers

nLowvoltageaudiosystems

ConnectionDiagrams

MSOP,SmallOutline,andDIPPackage

LLPPackage

10000802

TopView

OrderNumberLM4871MM,LM4871M,orLM4871NSeeNSPackageNumberMUA08A,M08A,orN08E

10000839

TopView

OrderNumberLM4871LD

SeeNSPackageNumberLDC08A

Boomer®isaregisteredtrademarkofNationalSemiconductorCorporation.

©2004NationalSemiconductorCorporationDS100008www.national.com

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LM4871TypicalApplication

10000801

FIGURE1.TypicalAudioAmplifierApplicationCircuit

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LM4871AbsoluteMaximumRatings(Note2)

IfMilitary/Aerospacespecifieddevicesarerequired,pleasecontacttheNationalSemiconductorSalesOffice/Distributorsforavailabilityandspecifications.SupplyVoltageSupplyTemperatureInputVoltage

PowerDissipation(Note4)ESDSusceptibility(Note5)ESDSusceptibility(Note6)JunctionTemperatureSolderingInformationSmallOutlinePackageVaporPhase(60sec.)Infrared(15sec.)

215˚C220˚C6.0V

−65˚Cto+150˚C−0.3VtoVDDto+0.3V

InternallyLimited

5000V250V150˚C

θJC(typ)—M08AθJA(typ)—M08AθJC(typ)—N08EθJA(typ)—N08EθJC(typ)—MUA08AθJA(typ)—MUA08AθJC(typ)—LDC08AθJA(typ)—LDC08A

35˚C/W140˚C/W37˚C/W107˚C/W56˚C/W210˚C/W4.3˚C/W

56˚C/W(Note9)

OperatingRatings

TemperatureRangeTMIN≤TA≤TMAXSupplyVoltage

−40˚C≤TA≤85˚C2.0V≤VDD≤5.5V

ElectricalCharacteristics(Notes2,3)

ThefollowingspecificationsapplyforVDD=5VandRL=8Ωunlessotherwisespecified.LimitsapplyforTA=25˚C.

LM4871

SymbolVDDIDDISDVOSPoParameter

SupplyVoltage

QuiescentPowerSupplyCurrent

ShutdownCurrentOutputOffsetVoltageOutputPower

VIN=0V,Io=0AVPIN1=VDDVIN=0V

THD=1%,f=1kHz

LM4871LD,RL=3Ω(Note10)LM4871LD,RL=4Ω(Note10)LM4871,RL=8Ω(Note10)THD+N=10%,f=1kHz

LM4871LD,RL=3Ω(Note10)LM4871LD,RL=4Ω(Note10)LM4871,RL=8Ω(Note10)

THD+N

TotalHarmonicDistortion+NoisePowerSupplyRejectionRatio

20Hz≤f≤20kHz,AVD=2

LM4871LD,RL=4Ω,PO=1.6WLM4871,RL=8Ω,PO=1WVDD=4.9Vto5.1V

2.3821.2

32.51.50.130.2560

W

Conditions

Min(Note7)2.0

6.50.65.0Typical(Note8)

Limit(Note7)5.510.0250

Units(Limits)VmAµAmV

W

%dB

PSRR

Note2:AbsoluteMaximumRatingsindicatelimitsbeyondwhichdamagetothedevicemayoccur.OperatingRatingsindicateconditionsforwhichthedeviceisfunctional,butdonotguaranteespecificperformancelimits.ElectricalCharacteristicsstateDCandACelectricalspecificationsunderparticulartestconditionswhichguaranteespecificperformancelimits.ThisassumesthatthedeviceiswithintheOperatingRatings.Specificationsarenotguaranteedforparameterswherenolimitisgiven,however,thetypicalvalueisagoodindicationofdeviceperformance.

Note3:Allvoltagesaremeasuredwithrespecttothegroundpin,unlessotherwisespecified.

Note4:ThemaximumpowerdissipationmustbederatedatelevatedtemperaturesandisdictatedbyTJMAX,θJA,andtheambienttemperatureTA.ThemaximumallowablepowerdissipationisPDMAX=(TJMAX–TA)/θJAorthenumbergiveninAbsoluteMaximumRatings,whicheverislower.FortheLM4871,TJMAX=150˚C.FortheθJA’sfordifferentpackages,pleaseseetheApplicationInformationsectionortheAbsoluteMaximumRatingssection.Note5:Humanbodymodel,100pFdischargedthrougha1.5kΩresistor.Note6:MachineModel,220pF–240pFdischargedthroughallpins.Note7:Typicalsarespecifiedat25˚Candrepresenttheparametricnorm.

Note8:LimitsareguaranteedtoNational’sAOQL(AverageOutgoingQualityLevel).

Note9:ThegivenθJAisforanLM4871packagedinanLDC08AwiththeExposed–DAPsolderedtoanexposed1in2areaof1ozprintedcircuitboardcopper.Note10:Whendriving3Ωor4Ωloadsfroma5Vsupply,theLM4871LDmustbemountedtoacircuitboard.

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LM4871ExternalComponentsDescription

(Figure1)Components1.2.

RiCiFunctionalDescription

Invertinginputresistancethatsetstheclosed-loopgaininconjunctionwithRf.ThisresistoralsoformsahighpassfilterwithCiatfC=1/(2πRiCi).

InputcouplingcapacitorthatblockstheDCvoltageattheamplifiersinputterminals.AlsocreatesahighpassfilterwithRiatfc=1/(2πRiCi).Refertothesection,ProperSelectionofExternalComponents,foranexplanationofhowtodeterminethevalueofCi.

Feedbackresistancethatsetstheclosed-loopgaininconjunctionwithRi.

Supplybypasscapacitorthatprovidespowersupplyfiltering.RefertothePowerSupplyBypassingsectionforinformationconcerningproperplacementandselectionofthesupplybypasscapacitor.

Bypasspincapacitorthatprovideshalf-supplyfiltering.Refertothesection,ProperSelectionofExternalComponents,forinformationconcerningproperplacementandselectionofCB.

3.4.5.

RfCSCBTypicalPerformanceCharacteristicsLDSpecificCharacteristics

LM4871LD

THD+NvsOutputPower

LM4871LD

THD+NvsFrequency

10000824

10000823

LM4871LD

THD+NvsFrequencyLM4871LD

THD+NvsOutputPower

10000825

10000826

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LM4871TypicalPerformanceCharacteristicsLDSpecificCharacteristics(Continued)

LM4871LD

PowerDissipationvsOutputPower

LM4871LD(Note11)PowerDeratingCurve

1000082710000828

Note11:ThiscurveshowstheLM4871LD’sthermaldissipationabilityatdifferentambienttemperaturesgiventheexposed-DAPofthepartissolderedtoaplaneof1oz.Cuwithanareagiveninthelabelofeachcurve.Thislabelalsodesignateswhethertheplaneexistsonthesame(top)layerasthechip,onthebottomlayer,oronbothlayers.Infiniteheatsinkandunattached(noheatsink)conditionsarealsoshown.

TypicalPerformanceCharacteristicsNon-LDSpecificCharacteristics

THD+NvsFrequency

THD+NvsFrequency

1000080310000804

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LM4871TypicalPerformanceCharacteristicsNon-LDSpecificCharacteristics(Continued)

THD+NvsFrequency

THD+NvsOutputPower

1000080510000806

THD+NvsOutputPowerTHD+NvsOutputPower

1000080710000808

OutputPowervsSupplyVoltageOutputPowervsSupplyVoltage

1000080910000810

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LM4871TypicalPerformanceCharacteristicsNon-LDSpecificCharacteristics(Continued)

OutputPowervsSupplyVoltage

OutputPowervsLoadResistance

1000081110000812

PowerDissipationvs

OutputPower

PowerDeratingCurve

1000081310000814

ClippingVoltagevsSupplyVoltage

NoiseFloor

10000815

10000816

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LM4871TypicalPerformanceCharacteristicsNon-LDSpecificCharacteristics(Continued)

FrequencyResponsevsInputCapacitorSize

PowerSupplyRejectionRatio

1000081710000818

OpenLoop

FrequencyResponseSupplyCurrentvsSupplyVoltage

10000819

10000820

ApplicationInformation

EXPOSED-DAPPACKAGEPCBMOUNTINGCONSIDERATION

TheLM4871’sexposed-DAP(dieattachpaddle)package(LD)providesalowthermalresistancebetweenthedieandthePCBtowhichthepartismountedandsoldered.ThisallowsrapidheattransferfromthedietothesurroundingPCBcoppertraces,groundplane,andsurroundingair.Theresultisalowvoltageaudiopoweramplifierthatproduces2Wat≤1%THDwitha4Ωload.Thishighpowerisachievedthroughcarefulconsiderationofnecessarythermaldesign.FailingtooptimizethermaldesignmaycompromisetheLM4871’shighpowerperformanceandactivateunwanted,thoughnecessary,thermalshutdownprotection.

TheLDpackagemusthaveitsDAPsolderedtoacopperpadonthePCB.TheDAP’sPCBcopperpadisconnectedtoalargeplaneofcontinuousunbrokencopper.Thisplaneformsathermalmass,heatsink,andradiationarea.Placetheheatsinkareaoneitheroutsideplaneinthecaseofa

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8

two-sidedPCB,oronaninnerlayerofaboardwithmorethantwolayers.ConnecttheDAPcopperpadtotheinnerlayerorbacksidecopperheatsinkareawith4(2x2)vias.Theviadiametershouldbe0.012in-0.013inwitha1.27mmpitch.Ensureefficientthermalconductivitybyplatingthroughthevias.

Bestthermalperformanceisachievedwiththelargestprac-ticalheatsinkarea.IftheheatsinkandamplifiersharethesamePCBlayer,anominal2.5in2areaisnecessaryfor5Voperationwitha4Ωload.HeatsinkareasnotplacedonthesamePCBlayerastheLM4871shouldbe5in2(min)forthesamesupplyvoltageandloadresistance.Thelasttwoarearecommendationsapplyfor25˚Cambienttemperature.In-creasetheareatocompensateforambienttemperaturesabove25˚C.TheLM4871’spowerde-ratingcurveintheTypicalPerformanceCharacteristicsshowsthemaximumpowerdissipationversustemperature.AnexamplePCBlay-outfortheLDpackageisshownintheDemonstrationBoardLayoutsection.Furtherdetailedandspecificinfor-mationconcerningPCBlayout,fabrication,andmountingan

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LM4871ApplicationInformation

(Continued)

LD(LLP)packageisavailablefromNationalSemiconduc-tor’sPackageEngineeringGroupunderapplicationnoteAN1187.

PCBLAYOUTANDSUPPLYREGULATION

CONSIDERATIONSFORDRIVING3ΩAND4ΩLOADSPowerdissipatedbyaloadisafunctionofthevoltageswingacrosstheloadandtheload’simpedance.Asloadimped-ancedecreases,loaddissipationbecomesincreasinglyde-pendantontheinterconnect(PCBtraceandwire)resistancebetweentheamplifieroutputpinsandtheload’sconnec-tions.Residualtraceresistancecausesavoltagedrop,whichresultsinpowerdissipatedinthetraceandnotintheloadasdesired.Forexample,0.1Ωtraceresistancereducestheoutputpowerdissipatedbya4Ωloadfrom2.0Wto1.95W.Thisproblemofdecreasedloaddissipationisexac-erbatedasloadimpedancedecreases.Therefore,tomain-tainthehighestloaddissipationandwidestoutputvoltageswing,PCBtracesthatconnecttheoutputpinstoaloadmustbeaswideaspossible.

Poorpowersupplyregulationadverselyaffectsmaximumoutputpower.Apoorlyregulatedsupply’soutputvoltagedecreaseswithincreasingloadcurrent.Reducedsupplyvoltagecausesdecreasedheadroom,outputsignalclipping,andreducedoutputpower.Evenwithtightlyregulatedsup-plies,traceresistancecreatesthesameeffectsaspoorsupplyregulation.Therefore,makingthepowersupplytracesaswideaspossiblehelpsmaintainfulloutputvoltageswing.

BRIDGECONFIGURATIONEXPLANATION

AsshowninFigure1,theLM4871hastwooperationalamplifiersinternally,allowingforafewdifferentamplifierconfigurations.Thefirstamplifier’sgainisexternallyconfig-urable;thesecondamplifierisinternallyfixedinaunity-gain,invertingconfiguration.Theclosed-loopgainofthefirstam-plifierissetbyselectingtheratioofRftoRiwhilethesecondamplifier’sgainisfixedbythetwointernal40kΩresistors.Figure1showsthattheoutputofamplifieroneservesastheinputtoamplifiertwo,whichresultsinbothamplifierspro-ducingsignalsidenticalinmagnitude,but180˚outofphase.Consequently,thedifferentialgainfortheICis

AVD=2*(Rf/Ri)

BydrivingtheloaddifferentiallythroughoutputsVo1andVo2,anamplifierconfigurationcommonlyreferredtoas“bridgedmode”isestablished.Bridgedmodeoperationisdifferentfromtheclassicalsingle-endedamplifierconfigura-tionwhereonesideofitsloadisconnectedtoground.

Abridgeamplifierdesignhasafewdistinctadvantagesoverthesingle-endedconfiguration,asitprovidesdifferentialdrivetotheload,thusdoublingoutputswingforaspecifiedsupplyvoltage.Fourtimestheoutputpowerispossibleascomparedtoasingle-endedamplifierunderthesamecon-ditions.Thisincreaseinattainableoutputpowerassumesthattheamplifierisnotcurrentlimitedorclipped.Inordertochooseanamplifier’sclosed-loopgainwithoutcausingex-cessiveclipping,pleaserefertotheAudioPowerAmplifierDesignsection.

AnotheradvantageofthedifferentialbridgeoutputisnonetDCvoltageacrossload.ThisresultsfrombiasingVO1andVO2atthesameDCvoltage,inthiscaseVDD/2.Thiseliminatesthecouplingcapacitorthatsinglesupply,single-endedamplifiersrequire.Eliminatinganoutputcouplingca-pacitorinasingle-endedconfigurationforcesasinglesupply

9

amplifier’shalf-supplybiasvoltageacrosstheload.Thecurrentflowcreatedbythehalf-supplybiasvoltagein-creasesinternalICpowerdissipationandmypermanentlydamageloadssuchasspeakers.POWERDISSIPATION

Powerdissipationisamajorconcernwhendesigningasuccessfulamplifier,whethertheamplifierisbridgedorsingle-ended.Adirectconsequenceoftheincreasedpowerdeliveredtotheloadbyabridgeamplifierisanincreaseininternalpowerdissipation.Equation1statesthemaximumpowerdissipationpointforabridgeamplifieroperatingatagivensupplyvoltageanddrivingaspecifiedoutputload.

PDMAX=4*(VDD)2/(2π2RL)(1)SincetheLM4871hastwooperationalamplifiersinone

package,themaximuminternalpowerdissipationis4timesthatofasingle-endedampifier.Evenwiththissubstantialincreaseinpowerdissipation,theLM4871doesnotrequireheatsinkingundermostoperatingconditionsandoutputloading.FromEquation1,assuminga5Vpowersupplyandan8Ωload,themaximumpowerdissipationpointis625mW.ThemaximumpowerdissipationpointobtainedfromEquation1mustnotbegreaterthanthepowerdissi-pationthatresultsfromEquation2:

(2)PDMAX=(TJMAX–TA)/θJAFortheSOpackage,θJA=140˚C/W,fortheDIPpackage,θJA=107˚C/W,andfortheMSOPpackage,θJA=210˚C/Wassumingfreeairoperation.FortheLDpackagesolderedtoaDAPpadthatexpandstoacopperareaof1.0in2onaPCB,theLM4871’sθJAis56˚C/W.TJMAX=150˚CfortheLM4871.TheθJAcanbedecreasedbyusingsomeformofheatsinking.TheresultantθJAwillbethesummationoftheθJC,θCS,andθSA.θJCisthejunctiontocaseofthepackage(ortotheexposedDAP,asisthecasewiththeLDpackage),θCSisthecasetoheatsinkthermalresistanceandθSAistheheatsinktoambientthermalresistance.Byaddingaddi-tionalcopperareaaroundtheLM4871,theθJAcanbereducedfromitsfreeairvaluefortheSOandMSOPpack-ages.IncreasingthecopperareaaroundtheLDpackagefrom1.0in2to2.0in2arearesultsinaθJAdecreaseto46˚C/W.Dependingontheambienttemperature,TA,andtheθJA,Equation2canbeusedtofindthemaximuminternalpowerdissipationsupportedbytheICpackaging.IftheresultofEquation1isgreaterthanthatofEquation2,theneitherthesupplyvoltagemustbedecreased,theloadim-pedanceincreased,theθJAdecreased,ortheambienttem-peraturereduced.Forthetypicalapplicationofa5Vpowersupply,withan8Ωload,andnoadditionalheatsinking,themaximumambienttemperaturepossiblewithoutviolatingthemaximumjunctiontemperatureisapproximately61˚Cpro-videdthatdeviceoperationisaroundthemaximumpowerdissipationpointandassumingsurfacemountpackaging.FortheLDpackageinatypicalapplicationofa5Vpowersupply,witha4Ωload,and1.0in2copperareasolderedtotheexposedDAPpad,themaximumambienttemperatureisapproximately77˚Cprovidingdeviceoperationisaroundthemaximumpowerdissipationpoint.Internalpowerdissipationisafunctionofoutputpower.Iftypicaloperationisnotaroundthemaximumpowerdissipationpoint,theambienttemperaturecanbeincreased.RefertotheTypicalPerfor-manceCharacteristicscurvesforpowerdissipationinfor-mationfordifferentoutputpowersandoutputloading.

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LM4871ApplicationInformation

POWERSUPPLYBYPASSING

(Continued)

firstorderhighpassfilterwhichlimitslowfrequencyre-sponse.Thisvalueshouldbechosenbasedonneededfrequencyresponseforafewdistinctreasons.

SelectionOfInputCapacitorSize

Largeinputcapacitorsarebothexpensiveandspacehungryforportabledesigns.Clearly,acertainsizedcapacitorisneededtocoupleinlowfrequencieswithoutsevereattenu-ation.Butinmanycasesthespeakersusedinportablesystems,whetherinternalorexternal,havelittleabilitytoreproducesignalsbelow100Hzto150Hz.Thus,usingalargeinputcapacitormaynotincreaseactualsystemperfor-mance.

Inadditiontosystemcostandsize,clickandpopperfor-manceiseffectedbythesizeoftheinputcouplingcapacitor,Ci.AlargerinputcouplingcapacitorrequiresmorechargetoreachitsquiescentDCvoltage(nominally1/2VDD).Thischargecomesfromtheoutputviathefeedbackandisapttocreatepopsupondeviceenable.Thus,byminimizingthecapacitorsizebasedonnecessarylowfrequencyresponse,turn-onpopscanbeminimized.

Besidesminimizingtheinputcapacitorsize,carefulconsid-erationshouldbepaidtothebypasscapacitorvalue.Bypasscapacitor,CB,isthemostcriticalcomponenttominimizeturn-onpopssinceitdetermineshowfasttheLM4871turnson.TheslowertheLM4871’soutputsramptotheirquiescentDCvoltage(nominally1/2VDD),thesmallertheturn-onpop.ChoosingCBequalto1.0µFalongwithasmallvalueofCi(intherangeof0.1µFto0.39µF),shouldproduceavirtuallyclicklessandpoplessshutdownfunction.Whilethedevicewillfunctionproperly,(nooscillationsormotorboating),withCBequalto0.1µF,thedevicewillbemuchmoresusceptibletoturn-onclicksandpops.Thus,avalueofCBequalto1.0µFisrecommendedinallbutthemostcostsensitivedesigns.

AUDIOPOWERAMPLIFIERDESIGNDesigna1W/8ΩAudioAmplifierGiven:

PowerOutputLoadImpedanceInputLevelInputImpedanceBandwidth

1Wrms

8Ω1Vrms20kΩ

100Hz–20kHz±0.25dB

Aswithanyamplifier,propersupplybypassingiscriticalforlownoiseperformanceandhighpowersupplyrejection.ThecapacitorlocationonboththebypassandpowersupplypinsshouldbeasclosetotheLM4871aspossible.Thecapacitorconnectedbetweenthebypasspinandgroundimprovestheinternalbiasvoltage’sstability,producingimprovedPSRR.TheimprovementstoPSRRincreaseasthebypasspincapacitorincreases.Typicalapplicationsemploya5Vregu-latorwith10µFanda0.1µFbypasscapacitorswhichaidinsupplystability.Thisdoesnoteliminatetheneedforbypass-ingthesupplynodesoftheLM4871witha1µFtantalumcapacitor.Theselectionofbypasscapacitors,especiallyCB,isdependentuponPSRRrequirements,clickandpopper-formanceasexplainedinthesection,ProperSelectionofExternalComponents,systemcost,andsizeconstraints.SHUTDOWNFUNCTION

Inordertoreducepowerconsumptionwhilenotinuse,theLM4871containsashutdownpintoexternallyturnofftheamplifier’sbiascircuitry.Thisshutdownfeatureturnstheamplifieroffwhenalogichighisplacedontheshutdownpin.Thetriggerpointbetweenalogiclowandlogichighlevelistypicallyhalf-supply.Itisbesttoswitchbetweengroundandsupplytoprovidemaximumdeviceperformance.Byswitch-ingtheshutdownpintoVDD,theLM4871supplycurrentdrawwillbeminimizedinidlemode.WhilethedevicewillbedisabledwithshutdownpinvoltageslessthenVDD,theidlecurrentmaybegreaterthanthetypicalvalueof0.6µA.Ineithercase,theshutdownpinshouldbetiedtoadefinitevoltagetoavoidunwantedstatechanges.

Inmanyapplications,amicrocontrollerormicroprocessoroutputisusedtocontroltheshutdowncircuitrywhichpro-videsaquick,smoothtransitionintoshutdown.Anotherso-lutionistouseasingle-pole,single-throwswitchinconjunc-tionwithanexternalpull-upresistor.Whentheswitchisclosed,theshutdownpinisconnectedtogroundanden-ablestheamplifier.Iftheswitchisopen,thentheexternalpull-upresistorwilldisabletheLM4871.Thisschemeguar-anteesthattheshutdownpinwillnotfloatthuspreventingunwantedstatechanges.

PROPERSELECTIONOFEXTERNALCOMPONENTSProperselectionofexternalcomponentsinapplicationsus-ingintegratedpoweramplifiersiscriticaltooptimizedeviceandsystemperformance.WhiletheLM4871istolerantofexternalcomponentcombinations,considerationtocompo-nentvaluesmustbeusedtomaximizeoverallsystemqual-ity.

TheLM4871isunity-gainstablewhichgivesadesignermaximumsystemflexibility.TheLM4871shouldbeusedinlowgainconfigurationstominimizeTHD+Nvalues,andmaximizethesignaltonoiseratio.Lowgainconfigurationsrequirelargeinputsignalstoobtainagivenoutputpower.Inputsignalsequaltoorgreaterthan1Vrmsareavailablefromsourcessuchasaudiocodecs.Pleaserefertothesection,AudioPowerAmplifierDesign,foramorecom-pleteexplanationofpropergainselection.

Besidesgain,oneofthemajorconsiderationsistheclosed-loopbandwidthoftheamplifier.Toalargeextent,theband-widthisdictatedbythechoiceofexternalcomponentsshowninFigure1.Theinputcouplingcapacitor,Ci,formsa

Adesignermustfirstdeterminetheminimumsupplyrailtoobtainthespecifiedoutputpower.ByextrapolatingfromtheOutputPowervsSupplyVoltagegraphsintheTypicalPer-formanceCharacteristicssection,thesupplyrailcanbeeasilyfound.Asecondwaytodeterminetheminimumsup-plyrailistocalculatetherequiredVopeakusingEquation3andaddtheoutputvoltage.Usingthismethod,theminimumsupplyvoltagewouldbe(Vopeak+(VODTOP+VODBOT)),whereVODBOTandVODTOPareextrapolatedfromtheDropoutVolt-agevsSupplyVoltagecurveintheTypicalPerformanceCharacteristicssection.

(3)

UsingtheOutputPowervsSupplyVoltagegraphforan8Ωload,theminimumsupplyrailis4.6V.Butsince5Visastandardvoltageinmostapplications,itischosenforthesupplyrail.Extrasupplyvoltagecreatesheadroomthatal-10

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LM4871ApplicationInformation

(Continued)

lowstheLM4871toreproducepeaksinexcessof1Wwith-outproducingaudibledistortion.Atthistime,thedesignermustmakesurethatthepowersupplychoicealongwiththeoutputimpedancedoesnotviolatetheconditionsexplainedinthePowerDissipationsection.

Oncethepowerdissipationequationshavebeenaddressed,therequireddifferentialgaincanbedeterminedfromEqua-tion4.

istoaddressthebandwidthrequirementswhichmustbestatedasapairof−3dBfrequencypoints.Fivetimesawayfroma−3dBpointis0.17dBdownfrompassbandresponsewhichisbetterthantherequired±0.25dBspecified.

fL=100Hz/5=20HzfH=20kHz*5=100kHz

AsstatedintheExternalComponentssection,Riincon-junctionwithCicreateahighpassfilter.

Ci≥1/(2π*20kΩ*20Hz)=0.397µF;use0.39µFThehighfrequencypoleisdeterminedbytheproductofthedesiredfrequencypole,fH,andthedifferentialgain,AVD.WithaAVD=3andfH=100kHz,theresultingGBWP=150kHzwhichismuchsmallerthantheLM4871GBWPof4MHz.Thisfiguredisplaysthatifadesignerhasaneedtodesignanamplifierwithahigherdifferentialgain,theLM4871canstillbeusedwithoutrunningintobandwidthlimitations.

(4)

(5)Rf/Ri=AVD/2

FromEquation4,theminimumAVDis2.83;useAVD=3.Sincethedesiredinputimpedancewas20kΩ,andwithaAVDimpedanceof2,aratioof1.5:1ofRftoRiresultsinanallocationofRi=20kΩandRf=30kΩ.Thefinaldesignstep

DemonstrationBoardLayout

10000829

FIGURE2.RecommendedLDPCBoardLayout:

Component-SideSilkscreen

10000831

FIGURE4.RecommendedLDPCBoardLayout:

Bottom-SideLayout

10000830

FIGURE3.RecommendedLDPCBoardLayout:

Component-SideLayout

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LM4871LM4871MDAMWA3WAudioPowerAmplifierWithShutdownMode

10000840

DieLayout(C-Step)

Die/WaferCharacteristics

FabricationAttributes

PhysicalDieIdentificationDieStep

LM4871CC

GeneralDieInformation

BondPadOpeningSize(min)BondPadMetalization

102µmx102µm0.5%

COPPER_BAL.ALUMINUMNITRIDEBAREBACKGND

PhysicalAttributes

WaferDiameterDiseSize(Drawn)ThicknessMinPitch

SpecialAssemblyRequirements:

Note:Actualdiesizeisroundedtothenearestmicron.

150mm

PassivationBackSideMetal

1372µmx1758µmBackSideConnection54milsx69mils406µmNominal1µmNominal

DieBondPadCoordinateLocations(C-Step)

(Referencedtodiecenter,coordinatesinµm)NC=NoConnection

SIGNALNAMESHUTDOWNBYPASSNCINPUT+INPUT-GNDVOUT1GNDVDDGNDVOUT2GND

PAD#NUMBER

1234567101112

X/YCOORDINATESX-559-559-559-559-559-476-135554554554-135-473

Y541376-45-248-486-725-598-686-4568598752

X102102102102102102102102102102102102

xxxxxxxxxxxxPADSIZE

Y102102210102102102210102210102210102

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LM4871LM4871MDAMWA3WAudioPowerAmplifierWithShutdownMode

(Continued)

INU.S.ATel#:Fax:INEUROPETel:Fax:

INASIAPACIFICTel:INJAPANTel:

810432992308(852)27371701

49(0)8141351492/149549(0)8141351470

1877DialDie1877342534312075416140

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LM4871PhysicalDimensions

inches(millimeters)unlessotherwisenoted

OrderNumberLM4871LD

SeeNSPackageNumberLDC08A

OrderNumberLM4871MNSPackageNumberM08A

www.national.com14

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LM4871PhysicalDimensions

inches(millimeters)unlessotherwisenoted(Continued)

OrderNumberLM4871MMNSPackageNumberMUA08A

OrderNumberLM4871NNSPackageNumberN08E

15www.national.com

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LM48713WAudioPowerAmplifierwithShutdownModeNotes

Nationaldoesnotassumeanyresponsibilityforuseofanycircuitrydescribed,nocircuitpatentlicensesareimpliedandNationalreservestherightatanytimewithoutnoticetochangesaidcircuitryandspecifications.Forthemostcurrentproductinformationvisitusatwww.national.com.LIFESUPPORTPOLICY

NATIONAL’SPRODUCTSARENOTAUTHORIZEDFORUSEASCRITICALCOMPONENTSINLIFESUPPORTDEVICESORSYSTEMSWITHOUTTHEEXPRESSWRITTENAPPROVALOFTHEPRESIDENTANDGENERALCOUNSELOFNATIONALSEMICONDUCTORCORPORATION.Asusedherein:

1.Lifesupportdevicesorsystemsaredevicesorsystemswhich,(a)areintendedforsurgicalimplantintothebody,or(b)supportorsustainlife,andwhosefailuretoperformwhenproperlyusedinaccordancewithinstructionsforuseprovidedinthelabeling,canbereasonablyexpectedtoresultinasignificantinjurytotheuser.BANNEDSUBSTANCECOMPLIANCE

NationalSemiconductorcertifiesthattheproductsandpackingmaterialsmeettheprovisionsoftheCustomerProductsStewardshipSpecification(CSP-9-111C2)andtheBannedSubstancesandMaterialsofInterestSpecification(CSP-9-111S2)andcontainno‘‘BannedSubstances’’asdefinedinCSP-9-111S2.

NationalSemiconductorAmericasCustomerSupportCenter

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

www.national.com

NationalSemiconductor

EuropeCustomerSupportCenter

Fax:+49(0)180-5308586Email:europe.support@nsc.com

DeutschTel:+49(0)6995086208EnglishTel:+44(0)8702402171FrançaisTel:+33(0)141918790

NationalSemiconductorAsiaPacificCustomerSupportCenter

Email:ap.support@nsc.com

NationalSemiconductor

JapanCustomerSupportCenterFax:81-3-5639-7507

Email:jpn.feedback@nsc.comTel:81-3-5639-7560

2.Acriticalcomponentisanycomponentofalifesupportdeviceorsystemwhosefailuretoperformcanbereasonablyexpectedtocausethefailureofthelifesupportdeviceorsystem,ortoaffectitssafetyoreffectiveness.

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IMPORTANTNOTICE

TexasInstrumentsIncorporatedanditssubsidiaries(TI)reservetherighttomakecorrections,modifications,enhancements,improvements,andotherchangestoitsproductsandservicesatanytimeandtodiscontinueanyproductorservicewithoutnotice.Customersshouldobtainthelatestrelevantinformationbeforeplacingordersandshouldverifythatsuchinformationiscurrentandcomplete.AllproductsaresoldsubjecttoTI’stermsandconditionsofsalesuppliedatthetimeoforderacknowledgment.

TIwarrantsperformanceofitshardwareproductstothespecificationsapplicableatthetimeofsaleinaccordancewithTI’sstandardwarranty.TestingandotherqualitycontroltechniquesareusedtotheextentTIdeemsnecessarytosupportthiswarranty.Exceptwheremandatedbygovernmentrequirements,testingofallparametersofeachproductisnotnecessarilyperformed.

TIassumesnoliabilityforapplicationsassistanceorcustomerproductdesign.Customersareresponsiblefortheirproductsand

applicationsusingTIcomponents.Tominimizetherisksassociatedwithcustomerproductsandapplications,customersshouldprovideadequatedesignandoperatingsafeguards.

TIdoesnotwarrantorrepresentthatanylicense,eitherexpressorimplied,isgrantedunderanyTIpatentright,copyright,maskworkright,orotherTIintellectualpropertyrightrelatingtoanycombination,machine,orprocessinwhichTIproductsorservicesareused.InformationpublishedbyTIregardingthird-partyproductsorservicesdoesnotconstitutealicensefromTItousesuchproductsorservicesorawarrantyorendorsementthereof.Useofsuchinformationmayrequirealicensefromathirdpartyunderthepatentsorotherintellectualpropertyofthethirdparty,oralicensefromTIunderthepatentsorotherintellectualpropertyofTI.

ReproductionofTIinformationinTIdatabooksordatasheetsispermissibleonlyifreproductioniswithoutalterationandisaccompaniedbyallassociatedwarranties,conditions,limitations,andnotices.Reproductionofthisinformationwithalterationisanunfairanddeceptivebusinesspractice.TIisnotresponsibleorliableforsuchaltereddocumentation.Informationofthirdpartiesmaybesubjecttoadditionalrestrictions.

ResaleofTIproductsorserviceswithstatementsdifferentfromorbeyondtheparametersstatedbyTIforthatproductorservicevoidsallexpressandanyimpliedwarrantiesfortheassociatedTIproductorserviceandisanunfairanddeceptivebusinesspractice.TIisnotresponsibleorliableforanysuchstatements.

TIproductsarenotauthorizedforuseinsafety-criticalapplications(suchaslifesupport)whereafailureoftheTIproductwouldreasonablybeexpectedtocauseseverepersonalinjuryordeath,unlessofficersofthepartieshaveexecutedanagreementspecificallygoverningsuchuse.Buyersrepresentthattheyhaveallnecessaryexpertiseinthesafetyandregulatoryramificationsoftheirapplications,and

acknowledgeandagreethattheyaresolelyresponsibleforalllegal,regulatoryandsafety-relatedrequirementsconcerningtheirproductsandanyuseofTIproductsinsuchsafety-criticalapplications,notwithstandinganyapplications-relatedinformationorsupportthatmaybeprovidedbyTI.Further,BuyersmustfullyindemnifyTIanditsrepresentativesagainstanydamagesarisingoutoftheuseofTIproductsinsuchsafety-criticalapplications.

TIproductsareneitherdesignednorintendedforuseinmilitary/aerospaceapplicationsorenvironmentsunlesstheTIproductsarespecificallydesignatedbyTIasmilitary-gradeor\"enhancedplastic.\"OnlyproductsdesignatedbyTIasmilitary-grademeetmilitary

specifications.BuyersacknowledgeandagreethatanysuchuseofTIproductswhichTIhasnotdesignatedasmilitary-gradeissolelyattheBuyer'srisk,andthattheyaresolelyresponsibleforcompliancewithalllegalandregulatoryrequirementsinconnectionwithsuchuse.TIproductsareneitherdesignednorintendedforuseinautomotiveapplicationsorenvironmentsunlessthespecificTIproductsaredesignatedbyTIascompliantwithISO/TS16949requirements.Buyersacknowledgeandagreethat,iftheyuseanynon-designatedproductsinautomotiveapplications,TIwillnotberesponsibleforanyfailuretomeetsuchrequirements.

FollowingareURLswhereyoucanobtaininformationonotherTexasInstrumentsproductsandapplicationsolutions:ProductsAudioAmplifiersDataConvertersDLP®ProductsDSP

ClocksandTimersInterfaceLogicPowerMgmtMicrocontrollersRFID

OMAPMobileProcessorsWirelessConnectivity

www.ti.com/audioamplifier.ti.comdataconverter.ti.comwww.dlp.comdsp.ti.comwww.ti.com/clocksinterface.ti.comlogic.ti.compower.ti.commicrocontroller.ti.comwww.ti-rfid.comwww.ti.com/omap

www.ti.com/wirelessconnectivity

TIE2ECommunityHomePage

e2e.ti.com

Applications

CommunicationsandTelecomwww.ti.com/communicationsComputersandPeripheralsConsumerElectronicsEnergyandLightingIndustrialMedicalSecurity

Space,AvionicsandDefenseVideoandImaging

www.ti.com/computerswww.ti.com/consumer-appswww.ti.com/energywww.ti.com/industrialwww.ti.com/medicalwww.ti.com/security

www.ti.com/space-avionics-defensewww.ti.com/video

TransportationandAutomotivewww.ti.com/automotive

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