LM4731Stereo25WAudioPowerAmplifierwithMuteandStandbyModesJuly2003
LM4731
Stereo25WAudioPowerAmplifierwithMuteandStandbyModes
GeneralDescription
TheLM4731isastereoaudioamplifiercapableofdeliveringtypically25Wperchannelofcontinuousaverageoutputpowerintoa4Ωor8Ωloadwithlessthan10%THD+Nfrom20Hz-20kHz.
Eachamplifierhasanindependentsmoothtransitionfade-in/outmuteandapowerconservingstandbymodewhichcanbecontrolledbyexternallogic.
TheLM4731hasshortcircuitprotectionandathermalshutdownfeaturethatisactivatedwhenthedietemperatureexceeds150˚C.TheLM4731alsohasaundervoltagelockoutfeatureforclickandpopfreepoweroffandon.
TheLM4731hasawideoperatingsupplyrangefrom+/-10V-+/-28Vallowingforlowercostunregulatedpowersuppliestobeused.
KeySpecifications
jOutputPowerinto4Ωor8Ω,10%THD+NjTHD+Nat1kHzwith2x1Winto8ΩjMuteAttenuation
jPSRRwithfRIPPLE=120Hz,
25W(typ)0.02%(typ)85dB(typ)50dB(typ)18V/µs(typ)4.8mA(typ)
VRIPPLE=1VRMSjSlewRate
jStandbyCurrent(+/-22V)
Features
nMinimalamountofexternalcomponentsnecessarynQuietfade-in/outmutemodenLowcurrentStandby-mode
Applications
nnnnnAudioAudioAudioAudioAudio
amplifieramplifieramplifieramplifieramplifier
forforforforfor
high-endstereoTVscomponentstereocompactstereo
PCsatellitespeakersystemsselfpoweredspeakers
ConnectionDiagrams
PlasticPackage
TO-220TopMarking(Note12)
20060375
20060352
TopView
Non-IsolatedPackageOrderNumberLM4731TASeeNSPackageNumberTA15A
TopView
U-WaferFabCodeZ-AssemblyPlantCode
XY-DateCodeTT-DieTraceabilityLM4731TA-LM4731TA
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LM4731TypicalApplication
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FIGURE1.TypicalAudioAmplifierApplicationCircuit
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LM4731AbsoluteMaximumRatings
2)
(Notes1,SolderingInformationTPackage(10sec.)StorageTemperatureThermalResistanceθJA(TA)θJC(TA)
43˚C/W1.5˚C/W260˚C
−40˚Cto+150˚C
IfMilitary/Aerospacespecifieddevicesarerequired,pleasecontacttheNationalSemiconductorSalesOffice/Distributorsforavailabilityandspecifications.SupplyVoltage|V|+|V|CommonModeInputVoltageDifferentialInputVoltageOutputCurrent
PowerDissipation(Note3)ESDSusceptability(Note4)ESDSusceptability(Note6)
JunctionTemperature(TJMAX)(Note9)
++-56VVorV
-56V
InternallyLimited
50W2.0kV250V150˚C
OperatingRatings(Notes1,2)
TemperatureRangeTMIN≤TA≤TMAXSupplyVoltage|V+|+|V-|
−20˚C≤TA≤+85˚C20V≤VTOTAL≤56V
ElectricalCharacteristics(Notes1,2)
ThefollowingspecificationsapplyforV+=+22V,V-=−22VandRL=8Ωunlessotherwisespecified.LimitsapplyforTA=25˚C.Symbol
Parameter
Conditions
LM4731
Typical(Note6)
|V+|+|V-|
PowerSupplyVoltage(Note10)GND−V-≥9V
Limit(Notes7,8)
2056
85
THD+N=10%(max),f=1kHz|V+|=|V-|=18V,RL=4Ω|V+|=|V-|=22V,RL=8ΩTHD+N=1%(max),f=1kHz|V+|=|V-|=18V,RL=4Ω|V+|=|V-|=22V,RL=8ΩPO=1W,f=1kHzAV=26dB,
|V+|=|V-|=18V,RL=4Ω|V+|=|V-|=22V,RL=8ΩPO=10Wf=1kHzf=10kHz
VIN=2.0Vp-p,trise=2nsVCM=0V,VO=0V,IO=0AStandbyoff(PlayMode)Standbyon(StandbyMode)VCM=0V,IO=0mAVCM=0V,IO=0mA
VRIPPLE=1VRMS,fRIPPLE=120Hzsinewave
InputsterminatedtoGNDRL=2kΩ,∆VO=20VIHF—A-WeightingFilterRIN=600Ω(InputReferred)
StandbyVILVIHMute
StandbyLowInputVoltageStandbyHighInputVoltage
NotinStandbyMode(Play)InStandbyMode
2.0
0.82.5
V(max)V(min)
25252020
20221818
V(min)V(max)dBW(min)W(min)W(min)W(min)Units(Limits)
AMMuteAttenuation
POOutputPower(RMS)
THD+N
TotalHarmonicDistortion+Noise
0.030.02656018954.82.00.2501102.0
0.50.3%(max)%(max)dBdBV/µs
XtalkSRIDDChannelSeparationSlewRate(Note11)
TotalQuiescentPowerSupplyCurrent
InputOffsetVoltageInputBiasCurrent
PowerSupplyRejectionRatio
110615
mA(max)mA(max)mV(max)
µAdBdB
VOSIBPSRR
AVOLeINOpenLoopVoltageGainInputNoise
8µV(max)
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LM4731ElectricalCharacteristics(Notes1,2)
+-(Continued)
ThefollowingspecificationsapplyforV=+22V,V=−22VandRL=8Ωunlessotherwisespecified.LimitsapplyforTA=25˚C.
Parameter
Conditions
LM4731
Typical(Note6)
Limit(Notes7,8)
0.8
2.0
2.5
V(max)V(min)Units(Limits)
Symbol
VILVIHMuteLowInputVoltageMuteHighInputVoltage
NotinMuteMode(Play)InMuteMode
Note1:Allvoltagesaremeasuredwithrespecttothegroundpin,unlessotherwisespecified.
Note2:AbsoluteMaximumRatingsindicatelimitsbeyondwhichdamagetothedevicemayoccur.OperatingRatingsindicateconditionsforwhichthedeviceisfunctional,butdonotguaranteespecificperformancelimits.ElectricalCharacteristicsstateDCandACelectricalspecificationsunderparticulartestconditionswhichguaranteespecificperformancelimits.ThisassumesthatthedeviceiswithintheOperatingRatings.Specificationsarenotguaranteedforparameterswherenolimitisgiven.However,thetypicalvalueisagoodindicationofadevice’sperformance.
Note3:Themaximumpowerdissipationmustbede-ratedatelevatedtemperaturesandisdictatedbyTJMAX,θJC,andtheambienttemperatureTA.ThemaximumallowablepowerdissipationisPDMAX=(TJMAX-TA)/θJCorthenumbergivenintheAbsoluteMaximumRatings,whicheverislower.FortheLM4731,TJMAX=150˚CandthetypicalθJCis1.5˚C/WfortheTA15Apackage.RefertotheThermalConsiderationssectionformoreinformation.Note4:Humanbodymodel,100pFdischargedthrougha1.5kΩresistor.Note5:MachineModel:a220pF-240pFdischargedthroughallpins.
Note6:Typicalspecificationsaresepcifiedat25˚Candrepresenttheparametricnorm.Note7:TestedlimitsareguaranteedtoNational’sAOQL(AverageOutgoingQualityLevel).
Note8:Datasheetmin/maxspecificationlimitsareguaranteedbydesign,test,orstatisticalanalysis.
Note9:Theoperatingjunctiontemperaturemaximumis150˚C.However,theinstantaneousSafeOperatingAreatemperatureis250˚C.
Note10:V-musthaveatleast-9VatitspinwithreferencetoGNDinorderfortheunder-voltageprotectioncircuitrytobedisabled.Inaddition,thevoltagedifferentialbetweenV+andV-mustbegreaterthan14V.
Note11:Thefeedbackcompensationnetworklimitsthebandwidthoftheclosed-loopresponsecausingtheskewratetobereducedbythehighfrequencyroll-off.Withoutfeedbackcompensationtheslewrateistypicallylarger.
Note12:TheLM4731TApackageTA15Aisanon-isolatedpackagesettingthetabofthedeviceandtheheatsinktoV-potentialwhentheLM4731TAisdirectlymountedtotheheatsinkusingonlythermalcompound.Ifamicawasherisusedinadditiontothermalcompound,θCS(casetosink)isincreased,buttheheatsinkwillbeelectricallyisolatedfromV-.
BridgedAmplifierApplicationCircuit
20060305
FIGURE2.BridgedAmplifierApplicationCircuit
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LM4731SingleSupplyApplicationCircuit
20060306
FIGURE3.SingleSupplyAmplifierApplicationCircuit
Note:*Optionalcomponentsdependentuponspecificdesignrequirements.
AuxiliaryAmplifierApplicationCircuit
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FIGURE4.SpecialAudioAmplifierApplicationCircuit
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LM4731ExternalComponentsDescription
(SeeFigures1-4)Components1
RBFunctionalDescription
Preventscurrentsfromenteringtheamplifier’snon-invertinginputwhichmaybepassedthroughtotheloaduponpowerdownofthesystemduetothelowinputimpedanceofthecircuitrywhentheundervoltagecircuitryisoff.Thisphenomenonoccurswhenthesupplyvoltagesarebelow1.5V.InvertinginputresistancetoprovideACgaininconjunctionwithRf.FeedbackresistancetoprovideACgaininconjunctionwithRi.
FeedbackcapacitorwhichensuresunitygainatDC.AlsocreatesahighpassfilterwithRiatfC=1/(2πRiCi).Providespowersupplyfilteringandbypassing.RefertotheSupplyBypassingapplicationsectionforproperplacementandselectionofbypasscapacitors.
Actsasavolumecontrolbysettingtheinputvoltagelevel.
Setstheamplifier’sinputterminalsDCbiaspointwhenCINispresentinthecircuit.AlsoworkswithCINtocreateahighpassfilteratfC=1/(2πRINCIN).RefertoFigure4.
Inputcapacitorwhichblockstheinputsignal’sDCoffsetsfrombeingpassedontotheamplifier’sinputs.WorkswithCSNtostabilizetheoutputstagebycreatingapolethatreduceshighfrequencyinstabilities.WorkswithRSNtostabilizetheoutputstagebycreatingapolethatreduceshighfrequencyinstabilities.ThepoleissetatfC=1/(2πRSNCSN).RefertoFigure4.
ProvideshighimpedanceathighfrequenciessothatRmaydecoupleahighlycapacitiveloadandreducetheQoftheseriesresonantcircuit.AlsoprovidesalowimpedanceatlowfrequenciestoshortoutRandpassaudiosignalstotheload.RefertoFigure4.
ProvidesDCvoltagebiasingforthetransistorQ1insinglesupplyoperation.Providesbiasfilteringforsinglesupplyoperation.
Limitsthevoltagedifferencebetweentheamplifier’sinputsforsinglesupplyoperation.RefertotheClicksandPopsapplicationsectionforamoredetailedexplanationofthefunctionofRINP.
Providesinputbiascurrentforsinglesupplyoperation.RefertotheClicksandPopsapplicationsectionforamoredetailedexplanationofthefunctionofRBI.
EstablishesafixedDCcurrentforthetransistorQ1insinglesupplyoperation.Thisresistorstabilizesthehalf-supplypointalongwithCA.
234567891011121314151617
RiRfCi(Note13)CSRV(Note13)RIN(Note13)CIN(Note13)RSN(Note13)CSN(Note13)L(Note13)R(Note13)RACARINP(Note13)RBIRENote13:Optionalcomponentsdependentuponspecificdesignrequirements.
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LM4731TypicalPerformanceCharacteristics
PSRRvsFrequency
SupplyCurrentvsSupplyVoltage
±22V,VRIPPLE=1VRMS,
RL=8Ω,80kHzBW
2006036820060365
THD+NvsFrequency±18V,PO=1W/Channel,RL=4Ω,80kHzBWTHD+NvsFrequency±22V,PO=1W/Channel,RL=8Ω,80kHzBW
2006036920060370
THD+NvsOutputPower±18V,RL=4Ω,80kHzBWTHD+NvsOutputPower±22V,RL=8Ω,80kHzBW
2006037120060372
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LM4731TypicalPerformanceCharacteristics
OutputPowervsSupplyVoltage
f=1kHz,RL=4Ω,80kHzBW
(Continued)
OutputPowervsSupplyVoltage
f=1kHz,RL=8Ω,80kHzBW
2006036320060364
PowerDissipationvs
OutputPower
1%THD(max),RL=4Ω,80kHzBWPowerDissipationvs
OutputPower
1%THD(max),RL=8Ω,80kHzBW
2006036120060362
CrosstalkvsFrequency
±18V,PO=10W,RL=4Ω,80kHzBWCrosstalkvsFrequency
±22V,PO=10W,RL=8Ω,80kHzBW
2006037320060374
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LM4731TypicalPerformanceCharacteristics
MuteAttenuationvsMutePinVoltage±22V,PO=1W,RL=8Ω,80kHzBW
(Continued)
StandbyAttenuationvsStandbyPinVoltage±22V,PO=1W,RL=8Ω,80kHzBW
2006036020060366
SupplyCurrentvsStandbyPinVoltage
±22V
20060367
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LM4731ApplicationInformation
MUTEMODE
Byplacingalogic-highvoltageonthemutepins,thesignalgoingintotheamplifierswillbemuted.Ifthemutepinsareleftfloatingorconnectedtoalogic-lowvoltage,theamplifi-erswillbeinanon-mutedstate.Therearetwomutepins,oneforeachamplifier,sothatonechannelcanbemutedwithoutmutingtheotheriftheapplicationrequiressuchaconfiguration.RefertotheTypicalPerformanceCharacter-isticssectionforcurvesconcerningMuteAttenuationvsMutePinVoltage.
STANDBYMODE
ThestandbymodeoftheLM4731allowstheusertodrasti-callyreducepowerconsumptionwhentheamplifiersareidle.Byplacingalogic-highvoltageonthestandbypins,theamplifierswillgointoStandbyMode.Inthismode,thecurrentdrawnfromtheVCCsupplyistypicallylessthan10µAtotalforbothamplifiers.ThecurrentdrawnfromtheVEEsupplyistypically4.8mA.Clearly,thereisasignificantre-ductioninidlepowerconsumptionwhenusingthestandbymode.TherearetwoStandbypins,sothatonechannelcanbeputinstandbymodewithoutputtingtheotheramplifierinstandbyiftheapplicationrequiressuchflexibility.RefertotheTypicalPerformanceCharacteristicssectionforcurvesshowingSupplyCurrentvs.StandbyPinVoltageforbothsupplies.
UNDER-VOLTAGEPROTECTION
Uponsystempower-up,theunder-voltageprotectioncir-cuitryallowsthepowersuppliesandtheircorrespondingcapacitorstocomeupclosetotheirfullvaluesbeforeturningontheLM4731suchthatnoDCoutputspikesoccur.Uponturn-off,theoutputoftheLM4731isbroughttogroundbeforethepowersuppliessuchthatnotransientsoccuratpower-down.
OVER-VOLTAGEPROTECTION
TheLM4731containsover-voltageprotectioncircuitrythatlimitstheoutputcurrentwhilealsoprovidingvoltageclamp-ing,thoughnotthroughinternalclampingdiodes.Theclamp-ingeffectisquitethesame,however,theoutputtransistorsaredesignedtoworkalternatelybysinkinglargecurrentspikes.
THERMALPROTECTION
TheLM4731hasasophisticatedthermalprotectionschemetopreventlong-termthermalstressofthedevice.Whenthetemperatureonthedieexceeds150˚C,theLM4731shutsdown.Itstartsoperatingagainwhenthedietemperaturedropstoabout145˚C,butifthetemperatureagainbeginstorise,shutdownwilloccuragainabove150˚C.Therefore,thedeviceisallowedtoheatuptoarelativelyhightemperatureifthefaultconditionistemporary,butasustainedfaultwillcausethedevicetocycleinaSchmittTriggerfashionbe-tweenthethermalshutdowntemperaturelimitsof150˚Cand145˚C.ThisgreatlyreducesthestressimposedontheICbythermalcycling,whichinturnimprovesitsreliabilityundersustainedfaultconditions.
Sincethedietemperatureisdirectlydependentupontheheatsinkused,theheatsinkshouldbechosensuchthatthermalshutdownwillnotbereachedduringnormalopera-tion.Usingthebestheatsinkpossiblewithinthecostand
spaceconstraintsofthesystemwillimprovethelong-termreliabilityofanypowersemiconductordevice,asdiscussedintheDeterminingtheCorrectHeatSinkSection.DETERMlNlNGMAXIMUMPOWERDISSIPATIONPowerdissipationwithintheintegratedcircuitpackageisaveryimportantparameterrequiringathoroughunderstand-ingifoptimumpoweroutputistobeobtained.Anincorrectmaximumpowerdissipationcalculationmayresultininad-equateheatsinkingcausingthermalshutdownandthuslimitingtheoutputpower.
Equation(1)exemplifiesthetheoreticalmaximumpowerdissipationpointofeachamplifierwhereVCCisthetotalsupplyvoltage.
(1)PDMAX=VCC2/2π2RLThusbyknowingthetotalsupplyvoltageandratedoutput
load,themaximumpowerdissipationpointcanbecalcu-lated.Thepackagedissipationistwicethenumberwhichresultsfromequation(1)sincetherearetwoamplifiersineachLM4731.RefertothegraphsofPowerDissipationversusOutputPowerintheTypicalPerformanceCharac-teristicssectionwhichshowtheactualfullrangeofpowerdissipationnotjustthemaximumtheoreticalpointthatre-sultsfromequation(1).
DETERMININGTHECORRECTHEATSINK
Thechoiceofaheatsinkforahigh-poweraudioamplifierismadeentirelytokeepthedietemperatureatalevelsuchthatthethermalprotectioncircuitrydoesnotoperateundernormalcircumstances.
Thethermalresistancefromthedie(junction)totheoutsideair(ambient)isacombinationofthreethermalresistances,θJC,θCS,andθSA.Inaddition,thethermalresistance,θJC(junctiontocase),oftheLM4731TAis1.5˚C/W.UsingTher-malloyThermacotethermalcompound,thethermalresis-tance,θCS(casetosink),isabout0.2˚C/W.Sinceconvectionheatflow(powerdissipation)isanalogoustocurrentflow,thermalresistanceisanalogoustoelectricalresistance,andtemperaturedropsareanalogoustovoltagedrops,thepowerdissipationoutoftheLM4731isequaltothefollowing:
(2)PDMAX=(TJMAX−TAMB)/θJAwhereTJMAX=150˚C,TAMBisthesystemambienttempera-tureandθJA=θJC+θCS+θSA.
Oncethemaximumpackagepowerdissipationhasbeencalculatedusingequation(1),themaximumthermalresis-tance,θSA,(heatsinktoambient)in˚C/Wforaheatsinkcanbecalculated.Thiscalculationismadeusingequation(3)whichisderivedbysolvingforθSAinequation(2).
θSA=[(TJMAX−TAMB)−PDMAX(θJC+θCS)]/PDMAX(3)AgainitmustbenotedthatthevalueofθSAisdependentuponthesystemdesigner’samplifierrequirements.Iftheambienttemperaturethattheaudioamplifieristobeworkingunderishigherthan25˚C,thenthethermalresistancefortheheatsink,givenallotherthingsareequal,willneedtobesmaller.
SUPPLYBYPASSING
TheLM4731hasexcellentpowersupplyrejectionanddoesnotrequirearegulatedsupply.However,toimprovesystemperformanceaswellaseliminatepossibleoscillations,theLM4731shouldhaveitssupplyleadsbypassedwithlow-inductancecapacitorshavingshortleadsthatarelocatedclosetothepackageterminals.Inadequatepowersupplybypassingwillmanifestitselfbyalowfrequencyoscillationknownas“motorboating”orbyhighfrequencyinstabilities.
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LM4731ApplicationInformation
(Continued)
Theseinstabilitiescanbeeliminatedthroughmultipleby-passingutilizingalargetantalumorelectrolyticcapacitor(10µForlarger)whichisusedtoabsorblowfrequencyvaria-tionsandasmallceramiccapacitor(0.1µF)topreventanyhighfrequencyfeedbackthroughthepowersupplylines.Ifadequatebypassingisnotprovided,thecurrentinthesupplyleadswhichisarectifiedcomponentoftheloadcurrentmaybefedbackintointernalcircuitry.Thissignalcausesdistortionathighfrequenciesrequiringthatthesup-pliesbebypassedatthepackageterminalswithanelectro-lyticcapacitorof470µFormore.
BRIDGEDAMPLIFIERAPPLICATION
TheLM4731hastwooperationalamplifiersinternally,allow-ingforafewdifferentamplifierconfigurations.Oneoftheseconfigurationsisreferredtoas“bridgedmode”andinvolvesdrivingtheloaddifferentiallythroughtheLM4731’soutputs.ThisconfigurationisshowninFigure2.Bridgedmodeop-erationisdifferentfromtheclassicalsingle-endedamplifierconfigurationwhereonesideofitsloadisconnectedtoground.
Abridgeamplifierdesignhasadistinctadvantageoverthesingle-endedconfiguration,asitprovidesdifferentialdrivetotheload,thusdoublingoutputswingforaspecifiedsupplyvoltage.Consequently,theoreticallyfourtimestheoutputpowerispossibleascomparedtoasingle-endedamplifierunderthesameconditions.Thisincreaseinattainableoutputpowerassumesthattheamplifierisnotcurrentlimitedorclipped.
Adirectconsequenceoftheincreasedpowerdeliveredtotheloadbyabridgeamplifierisanincreaseininternalpowerdissipation.Foreachoperationalamplifierinabridgecon-figuration,theinternalpowerdissipationwillincreasebyafactoroftwooverthesingleendeddissipation.Thus,foranaudiopoweramplifiersuchastheLM4731,whichhastwooperationalamplifiersinonepackage,thepackagedissipa-tionwillincreasebyafactoroffour.TocalculatetheLM4731’smaximumpowerdissipationpointforabridgedload,multiplyequation(1)byafactoroffour.
ThisvalueofPDMAXcanbeusedtocalculatethecorrectsizeheatsinkforabridgedamplifierapplication.Sincetheinter-naldissipationforagivenpowersupplyandloadisin-creasedbyusingbridged-mode,theheatsink’sθSAwillhavetodecreaseaccordinglyasshownbyequation(3).Refertothesection,DeterminingtheCorrectHeatSink,foramoredetaileddiscussionofproperheatsinkingforagivenappli-cation.
SINGLE-SUPPLYAMPLIFIERAPPLICATION
ThetypicalapplicationoftheLM4731isasplitsupplyam-plifier.ButasshowninFigure3,theLM4731canalsobeusedinasinglepowersupplyconfiguration.Thisinvolvesusingsomeexternalcomponentstocreateahalf-supplybiaswhichisusedasthereferencefortheinputsandoutputs.Thus,thesignalwillswingaroundhalf-supplymuchlikeitswingsaroundgroundinasplit-supplyapplication.Alongwithpropercircuitbiasing,afewotherconsiderationsmustbeaccountedfortotakeadvantageofalloftheLM4731functions.
TheLM4731possessesamuteandstandbyfunctionwithinternallogicgatesthatarehalf-supplyreferenced.Thus,toenableeithertheMuteorStandbyfunction,thevoltageatthesepinsmustbeaminimumof2.5Vabovehalf-supply.Insingle-supplysystems,devicessuchasmicroprocessorsandsimplelogiccircuitsusedtocontrolthemuteandstandbyfunctions,areusuallyreferencedtoground,nothalf-supply.Thus,tousethesedevicestocontrolthelogiccircuitryoftheLM4731,a“levelshifter,”liketheoneshowninFigure5,mustbeemployed.Alevelshifterisnotneededinasplit-supplyconfigurationsincegroundisalsohalf-supply.
20060354
FIGURE5.LevelShiftCircuit
WhenthevoltageattheLogicInputnodeis0V,the2N3904is“off”andthusresistorRcpullsupmuteorstandbyinputtothesupply.Thisenablesthemuteorstandbyfunction.WhentheLogicInputis5V,the2N3904is“on”andconsequently,thevoltageatthecollectorisessentially0V.Thiswilldisablethemuteorstandbyfunction,andthustheamplifierwillbeinitsnormalmodeofoperation.Rshift,alongwithCshift,createsanRCtimeconstantthatreducestransientswhenthemuteorstandbyfunctionsareenabledordisabled.Additionally,RshiftlimitsthecurrentsuppliedbytheinternallogicgatesoftheLM4731whichinsuresdevicereliability.RefertotheMuteModeandStandbyModesectionsintheApplicationInformationsectionforamoredetaileddescriptionofthesefunctions.
CLICKSANDPOPS
InthetypicalapplicationoftheLM4731asasplit-supplyaudiopoweramplifier,theICexhibitsexcellent“click”and“pop”performancewhenutilizingthemuteandstandbymodes.Inaddition,thedeviceemploysUnder-VoltagePro-tection,whicheliminatesunwantedpower-upandpower-downtransients.Thebasisforthesefunctionsareastableandconstanthalf-supplypotential.Inasplit-supplyapplica-tion,groundisthestablehalf-supplypotential.Butinasingle-supplyapplication,thehalf-supplyneedstochargeupjustlikethesupplyrail,VCC.Thismakesthetaskofattainingaclicklessandpoplessturn-onmorechallenging.Anyun-evenchargingoftheamplifierinputswillresultinoutputclicksandpopsduetothedifferentialinputtopologyoftheLM4731.
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LM4731ApplicationInformation
(Continued)
instabilityandusingtheLM4731forgainshigherthan50V/VwillseeanincreaseinnoiseandTHD.
ThecombinationofRiwithCi(seeFigure1)createsahighpassfilter.Thelowfrequencyresponseisdeterminedbythesetwocomponents.The-3dBpointcanbefoundfromEquation(5)shownbelow:
(5)fi=1/(2πRiCi)(Hz)IfaninputcouplingcapacitorisusedtoblockDCfromthe
inputsasshowninFigure4,therewillbeanotherhighpassfiltercreatedwiththecombinationofCINandRIN.WhenusingainputcouplingcapacitorRINisneededtosettheDCbiaspointontheamplifier’sinputterminal.Theresulting-3dBfrequencyresponseduetothecombinationofCINandRINcanbefoundfromEquation(6)shownbelow:
(6)fIN=1/(2πRINCIN)(Hz)PHYSICALICMOUNTINGCONSIDERATIONS
MountingoftheTO-220packagetoaheatsinkmustbedonesuchthatthereissufficientpressurefromthemountingscrewtoinsuregoodcontactwiththeheatsinkforefficientheatflow.OvertighteningthemountingscrewwillcausetheTO-220packagetowarpreducingcontactareawiththeheatsink.LesscontactwiththeheatsinkwillincreasethethermalresistancefromtheTO-220packagecasetotheheatsink(θCS)resultinginhigheroperatingdietemperaturesandpossibleunwantedthermalshutdownactivation.ExtremeovertighteningofthemountingscrewwillcauseseverephysicalstressresultingincrackeddieandcatastrophicICfailure.Therecommendedmaximummountingscrewtorqueis40inch-lbsor3.3foot-lbs(4.5newton-meter).
Additionally,ifthemountingscrewisusedtoforcetheTO-220packageintocorrectalignmentwiththeheatsink,pack-agestresswillbeincreased.Thisincreaseinpackagestresswillresultinreducedcontactareawiththeheatsinkincreas-ingdieoperatingtemperatureandpossiblecatastrophicICfailure.
Toachieveatransientfreepower-upandpower-down,thevoltageseenattheinputterminalsshouldbeideallythesame.Suchasignalwillbecommon-modeinnature,andwillberejectedbytheLM4731.InFigure3,theresistorRINPservestokeeptheinputsatthesamepotentialbylimitingthevoltagedifferencepossiblebetweenthetwonodes.Thisshouldsignificantlyreduceanytypeofturn-onpop,duetoanunevenchargingoftheamplifierinputs.Thischargingisbasedonaspecificapplicationloadingandthus,thesystemdesignermayneedtoadjustthesevaluesforoptimalperfor-mance.
AsshowninFigure3,theresistorslabeledRBIhelpbiasuptheLM4731offthehalf-supplynodeattheemitterofthe2N3904.Butduetotheinputandoutputcouplingcapacitorsinthecircuit,alongwiththenegativefeedback,therearetwodifferentvaluesofRBI,namely10kΩand200kΩ.Theseresistorsbringuptheinputsatthesamerateresultinginapoplessturn-on.Adjustingtheseresistorsvaluesslightlymayreducepopsresultingfrompowersuppliesthatrampextremelyquickorexhibitovershootduringsystemturn-on.PROPERSELECTIONOFEXTERNALCOMPONENTSProperselectionofexternalcomponentsisrequiredtomeetthedesigntargetsofanapplication.Thechoiceofexternalcomponentvaluesthatwillaffectgainandlowfrequencyresponsearediscussedbelow.
ThegainofeachamplifierissetbyresistorsRfandRiforthenon-invertingconfigurationshowninFigure1.ThegainisfoundbyEquation(4)below:
(4)AV=1+Rf/Ri(V/V)
Forbestnoiseperformance,lowervaluesofresistorsareused.Avalueof1kΩiscommonlyusedforRiandthensettingthevalueofRfforthedesiredgain.FortheLM4731thegainshouldbesetnolowerthan10V/Vandnohigherthan50V/V.Gainsettingsbelow10V/Vmayexperience
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LM4731ApplicationInformation
(Continued)
20060355
FIGURE6.ReferencePCBSchematic
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LM4731ApplicationInformation
CompositeView
(Continued)
LM4731REFERENCEBOARDARTWORK
SilkScreen
2006035620060357
TopLayerBottomLayer
20060358
20060359
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元器件交易网www.cecb2b.com
LM4731ApplicationInformation
SymbolRIN1,RIN2RB1,RB2RF1,RF2Ri1,Ri2RSN1,RSN2RGCIN1,CIN2Ci1,Ci2CSN1,CSN2CVCMCS1,CS2CS3,CS4CS5,CS6S1,S2J1,J2J4,J7,J8J3,J5,J6,J9U1U2Value47kΩ1kΩ20kΩ1kΩ4.7Ω2.7Ω1µF47µF0.1µF0.1µF10µF0.1µF10µF1,000µF
(Continued)
BILLOFMATERIALSFORREFERENCEPCB
Tolerance
5%1%1%1%5%5%10%20%20%20%20%20%20%20%
Type/Description
1/4Watt1/4Watt1/4Watt1/4Watt1/4Watt1/4Watt
MetallizedPolyesterFilmElectrolyticRadial/35VMonolithicCeramicMonolithicCeramicElectrolyticRadial/16VMonolithicCeramicElectrolyticRadial/35VElectrolyticRadial/35VSPDT(on-on)Switch
Non-switchedPCMountRCAJack
PCBBananaJack-BLACKPCBBananaJack-RED15leadTO-220PowerSocketLM340,5VFixedRegulator,TO-263
package(TS3B)
Comments
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LM4731Stereo25WAudioPowerAmplifierwithMuteandStandbyModesPhysicalDimensions
inches(millimeters)unlessotherwisenoted
Non-IsolatedTO-22015-LeadPackage
OrderNumberLM4731TANSPackageNumberTA15A
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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NationalSemiconductor
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2.Acriticalcomponentisanycomponentofalifesupportdeviceorsystemwhosefailuretoperformcanbereasonablyexpectedtocausethefailureofthelifesupportdeviceorsystem,ortoaffectitssafetyoreffectiveness.
NationalSemiconductorAsiaPacificCustomerSupportCenter
Email:ap.support@nsc.com
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JapanCustomerSupportCenterFax:81-3-5639-7507
Email:jpn.feedback@nsc.comTel:81-3-5639-7560
Nationaldoesnotassumeanyresponsibilityforuseofanycircuitrydescribed,nocircuitpatentlicensesareimpliedandNationalreservestherightatanytimewithoutnoticetochangesaidcircuitryandspecifications.
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