LM4668

LM4668

10WHigh-EfficiencyMonoBTLAudioPowerAmplifier

GeneralDescription

TheLM4668isahighefficiencyswitchingaudiopoweramplifierprimarilydesignedfordemandingapplicationsinflatpanelmonitorsandTV’s.Itiscapableofdelivering6Wtoan8ΩmonoBTLloadwithlessthan1%distortion(THD+N)froma12VDCpowersupply.

Boomeraudiopoweramplifiersweredesignedspecificallytoprovidehighqualityoutputpowerwithaminimalamountofexternalcomponents.TheLM4668featuresamicro-power,active-lowshutdownmode,aninternalthermalshutdownprotectionmechanism,andshortcircuitprotection.

TheLM4668containsadvancedtransient(“popandclick”)suppressioncircuitrythateliminatesnoisesthatwouldoth-erwiseoccurduringturn-onandturn-offtransitions.

KeySpecifications

jPowerOutputBTL(VDD=14V,

fIN=1kHz,THD+N=10%,RL=8Ω)

jQuiescentPowerSupplyCurrentjEfficiency(VDD=12V,fIN=1kHz,

10W(typ)30mA(typ)79%(typ)0.15mA(typ)30dB(typ)

RL=8Ω,POUT=6W)

jShutdownCurrentjFixedGain

Features

nSoft-startcircuitryeliminatesnoiseduringturn-ontransition

nLowcurrentshutdownmodenLowquiescentcurrentn6WBTLoutput,RL=8ΩnShortcircuitprotection

nFixed,internallysetgainof30dB

Applications

nFlatPanelMonitorsnFlatPanelTVs

nComputerSoundCards

ConnectionDiagrams

LDPackage

MHPackage

20089102

TopView

OrderNumberLM4668LD

SeeNSPackageNumberLDC14A

200891G3

TopView

OrderNumberLM4668MH

SeeNSPackageNumberMXA20A

Boomer®isaregisteredtrademarkofNationalSemiconductorCorporation.

©2004NationalSemiconductorCorporationDS200891www.national.com

LM4668TypicalApplication

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FIGURE1.TypicalAudioAmplifierApplicationCircuit(*ZetexZHCS506)

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LM4668AbsoluteMaximumRatings(Notes1,2)

IfMilitary/Aerospacespecifieddevicesarerequired,pleasecontacttheNationalSemiconductorSalesOffice/Distributorsforavailabilityandspecifications.SupplyVoltageStorageTemperatureInputVoltage

PowerDissipation(Note3)ESDSusceptibility(Note4)ESDSusceptibility(Note5)

16V

−65˚Cto+150˚C−0.3VtoVDD+0.3V

Internallylimited

2000V200V

JunctionTemperature(LDandMH)ThermalResistanceθJCθJA150˚C2˚C/W40˚C/W

OperatingRatings

TemperatureRangeTMIN≤TA≤TMAXSupplyVoltage(Note10)

−40˚C≤TA≤85˚C9V≤VDD≤14.0V

(Note1)

ThefollowingspecificationsapplyforthecircuitshowninFigure1operatingwithVDD=12V,RL=8Ω,andfIN=1kHz,unlessotherwisespecified.LimitsapplyforTA=25˚C.Symbol

Parameter

Conditions

LM4668Typical(Note6)

IDDISDAVQuiescentPowerSupplyCurrentShutdownCurrentAmplifierGain

VIN=0V,IO=0A,RL=8ΩVSHUTDOWN=GND(Note9)

BTLoutputvoltagewithrespecttoinputvoltage,VIN=100mVp-pTHD+N=1%(max)

THD+N=10%,VDD=14V

POUT=6W,postfilter,

-3dBrelativetotheoutputamplitudeat1kHz,SeeFigure1

POUT=6W,includingoutputfilterA-WeightedFilter,VIN=0VA-WeightedFilter,POUT=6WAV=30dB

VRIPPLE=20mVp-p,CBYPASS_1=10µF,inputreferredf=50Hzf=60Hzf=100Hzf=120Hzf=1kHzCBYPASS=10µF

300.15306100.220200007922090

32285Limit(Notes7,

8)65

mA(max)mAdB(max)dB(min)W(min)W%HzHz%µVdBUnits(Limits)

ElectricalCharacteristicsfortheLM4668

POTHD+NfBWOutputPower

TotalHarmonicDistortion+NoisePOUT=1WRMSFrequencyResponseBandwith

ηéNSNRPSRR

EfficiencyOutputNoiseSignal-to-NoiseRatioPowerSupplyRejectionRatio

7982858475600170

41.5

dB

tWUTSDVSDIHVSDILWake-Uptime

ThermalShutdownTemperatureShutdownVoltageInputHighShutdownVoltageInputLow

ms˚C(min)˚C(max)V(min)V(max)

Note1:AllvoltagesaremeasuredwithrespecttotheGNDpinunlessotherwisespecified.

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

Note3:Themaximumpowerdissipationmustbede-ratedatelevatedtemperaturesandisdictatedbyTJMAX,θJA,andtheambienttemperatureTA.ThemaximumallowablepowerdissipationisPDMAX=(TJMAX−TA)/θJAorthenumbergiveninAbsoluteMaximumRatings,whicheverislower.FortheLM4668typicalapplication(showninFigure1)withVDD=12V,RL=8Ωstereooperation,thetotalpowerdissipationis900mW.θJA=40˚C/WNote4:Humanbodymodel,100pFdischargedthrougha1.5kΩresistor.Note5:Machinemodel,220pF–240pFdischargedthroughallpins.Note6:Typicalsaremeasuredat25˚Candrepresenttheparametricnorm.

Note7:LimitsareguaranteedtoNational’sAOQL(AverageOutgoingQualityLevel).

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LM4668ElectricalCharacteristicsfortheLM4668

(Note1)(Continued)

Note8:Datasheetsmin/maxspecificationlimitsareguaranteedbydesign,test,orstatisticalanalysis.

Note9:Shutdowncurrentismeasuredinanormalroomenvironment.TheSHUTDOWNpinshouldbedrivenascloseaspossibletoGNDforminimumshutdowncurrent.

Note10:Pleasereferto“UnderVoltageProtection”onpage8under“GeneralFeatures.”

TypicalPerformanceCharacteristics

THD+NvsFrequencyVDD=9V,RL=8Ω,PO=1W

THD+NvsFrequencyVDD=12V,RL=8Ω,PO=1W

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THD+NvsFrequencyVDD=14V,RL=8Ω,PO=1WTHD+NvsOutputPowerRL=8Ω,VDD=9V,f=1kHz

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20089109

THD+NvsOutputPowerRL=8Ω,VDD=12V,f=1kHzTHD+NvsOutputPowerRL=8Ω,VDD=14V,f=1kHz

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LM4668TypicalPerformanceCharacteristics

AmplifierOutputPowervsPowerSupplyVoltage

RL=8Ω,f=1kHz

(Continued)

AmplifierOutputMagnitude

vsFrequencyRL=8Ω,VDD=12V

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PowerRejectionRatiovsFrequencyVDD=9V,RL=8Ω,InputReferredPowerRejectionRatiovsFrequencyVDD=12V,RL=8Ω,InputReferred

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PowerRejectionRatiovsFrequencyVDD=14V,RL=8Ω,InputReferred

AmplifierPowerDissipationvsAmplifierLoadDissipationVDD=14V,RL=8Ω,f=1kHz

20089116

20089117

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LM4668TypicalPerformanceCharacteristics

AmplifierPowerDissipationvsLoadPowerDissipationVDD=12V,RL=8Ω,f=1kHz

(Continued)

AmplifierPowerDissipationvsTotalLoadPowerDissipationVDD=9V,RL=8Ω,f=1kHz

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OutputPowervsLoadResistanceVDD=14V,f=1kHzOutputPowervsLoadResistanceVDD=12V,f=1kHz

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OutputPowervsLoadResistanceVDD=9V,f=1kHzPowerSupplyCurrentvsPowerSupplyVoltage

VIN=0V,RL=8Ω

20089122

20089123

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LM4668TypicalPerformanceCharacteristics

PowerDissipationvsAmbientTemperature

(Continued)

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LM4668GeneralFeatures

SYSTEMFUNCTIONALINFORMATIONModulationTechnique

UnliketypicalClassDamplifiersthatusesingle-endedcom-paratorstogenerateapulse-widthmodulatedswitchingwaveformandRCtimingcircuitstosettheswitchingfre-quency,theLM4668usesabalanceddifferentialfloatingmodulator.Oscillationisaresultofinjectingcomplimentarycurrentsontotherespectiveplatesofafloating,on-dieca-pacitor.Thevalueofthefloatingcapacitorandvalueofthecomponentsinthemodulator’sfeedbacknetworkandsetsthenominalswitchingfrequencyat450kHz.Modulationre-sultsfromimbalancesintheinjectedcurrents.Theamountofcurrentimbalanceisdirectlyproportionaltotheappliedinputsignal’smagnitudeandfrequency.

Usingabalanced,floatingmodulatorproducesaClassDamplifierthatisimmunetocommonmodenoisesourcessuchassubstratenoise.Thisnoiseoccursbecauseofthehighfrequency,highcurrentswitchingintheamplifier’sout-putstage.TheLM4668isimmunetothistypeofnoisebecausethemodulator,thecomponentsthatsetitsswitch-ingfrequency,andeventheloadallfloatwithrespecttoground.

Thebalancedmodulator’spulsewidthmodulatedoutputdrivesthegatesoftheLM4668’sH-bridgeconfiguredoutputpowerMOSFETs.Thepulse-trainpresentatthepowerMOSFETs’outputisappliedtoanLClowpassfilterthatremovesthe450kHzenergycomponent.Thefilter’soutputsignal,whichisappliedtothedrivenload,isanamplifiedreplicaoftheaudioinputsignal.

ShutdownFunction

TheLM4668’sactive-lowshutdownfunctionallowstheusertoplacetheamplifierinashutdownmodewhilethesystempowersupplyremainsactive.Activatingshutdowndeacti-vatestheoutputswitchingwaveformandminimizesthequiescentcurrent.Applyinglogic0(GND)topin8enablestheshutdownfunction.Applyinglogic1(4V≤VLOGIC≤VDD)topin8disablestheshutdownfunctionandrestoresfullamplifieroperation.

UnderVoltageProtection

Theundervoltageprotectiondisablestheoutputdriversec-tionoftheLM4668whilethesupplyvoltageisbelow8V.Thisconditionmayoccuraspowerisfirstappliedorduringlowlineconditions,changesinloadresistance,orwhenpowersupplysagoccurs.TheundervoltageprotectionensuresthatalloftheLM4668’spowerMOSFETsareoff.Thisactioneliminatesshoot-throughcurrentandminimizesoutputtran-sientsduringturn-onandturn-off.Theundervoltageprotec-tiongivesthedigitallogictimetostabilizeintoknownstates,furtherminimizingturnoutputtransients.

Turn-OnTime

TheLM4668hasaninternaltimerthatdeterminestheam-plifier’sturn-ontime.Afterpowerisfirstappliedorthepartreturnsfromshutdown,thenominalturn-ontimeis600ms.ThisdelayallowsallexternallyappliedcapacitorstochargetoafinalvalueofVDD/2.Further,duringturn-on,theoutputsaremuted.Thisminimizesoutputtransientsthatmayoccurwhilethepartsettlesintoisquiescentoperatingmode.

OutputStageFaultDetectionAndProtection

TheoutputstageMOSFETsareprotectedagainstoutputconditionsthatcouldotherwisecompromisetheiroperationalstatus.Anonboardfaultdetectioncircuitcontinuouslymoni-torsthesignaloneachoutputMOSFET’sgateandcom-paresitagainsttherespectivedrainvoltage.Whenacondi-tionisdetectedthatviolatesaMOSFET’sSafeOperatingArea(SOA),thedrivesignalisdisconnectedfromtheoutputMOSFETs’gates.Thefaultdetectcircuitmaintainsthispro-tectiveconditionforapproximately600ms,atwhichtimethedrivesignalisreconnected.Ifthefaultconditionisnolongerpresent,normaloperationresumes.

Ifthefaultconditionremains,however,thedrivesignalisagaindisconnected.

ThermalProtection

TheLM4668hasthermalshutdowncircuitrythatmonitorsthedietemperature.OncetheLM4668dietemperaturereaches170˚C,theLM4668disablestheoutputswitchingwaveformandremainsdisableduntilthedietemperaturefallsbelow140˚C(typ).

Over-ModulationProtection

TheLM4668’sover-modulationprotectionisaresultofthepreamplifier’s(AMP1andAMP2,Figure1)inabilitytopro-ducesignalmagnitudesthatequalthepowersupplyvolt-ages.Sincethepreamplifier’soutputmagnitudewillalwaysbelessthanthesupplyvoltage,thedutycycleoftheampli-fier’sswitchingoutputwillneverreachzero.Peakmodula-tionislimitedtoanominal95%.

ApplicationHints

SUPPLYBYPASSING

Correctpowersupplybypassinghastwoimportantgoals.Thefirstistoreducenoiseonthepowersupplylinesandminimizedeleteriouseffectsthatthenoisemaycausetotheamplifier’soperation.Thesecondistohelpstabilizeanunregulatedpowersupplyandtoimprovethesupply’stran-sientresponseunderheavycurrentdemands.Thesetwogoalsrequiredifferentcapacitorvalueranges.Therefore,varioustypesandvaluesarerecommendedforsupplyby-passing.Fornoisede-coupling,generallysmallceramicca-pacitors(0.01µFto0.1µF)arerecommended.Largervalue(1µFto10µF)tantalumcapacitorsareneededforthetran-sientcurrentdemands.Thesetwocapacitorsinparallelwilldoanadequatejobofremovingmostnoisefromthesupplyrailsandprovidingthenecessarytransientcurrent.ThesecapacitorsshouldbeplacedascloseaspossibletoeachIC’ssupplypin(s)usingleadsasshortaspossible.

TheLM4668hastwoVDDpins:apowerVDD(PVDD)andasignalVDD(SVDD).Theparallelcombinationofthelowvalueceramic(0.1µF)andhighvaluetantalum(10µF)shouldbeusedtobypassthePVDDpin.Asmallvalue(0.1µF)ceramicortantalumcanbeusedtobypasstheSVDDpin.

AMPLIFIEROUTPUTFILTERING

TheLM4668requiresalowpassfilterconnectedbetweentheamplifier’sbridgeoutputandtheload.Thesecond-orderLCoutputfiltershowninFigure1createsthelowpassre-sponsethatisnecessarytoattenuatesignalenergyattheamplifier’sswitchingfrequency.ItalsoservestosuppressEMI.Together,theoutputfilter’s0.27µFcapacitorsandtherecommendedminimuminductorvalueof27µHproducea

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LM4668ApplicationHints

(Continued)

THD+NMEASUREMENTSANDOUTOFAUDIOBANDNOISE

THD+N(TotalHarmonicDistortionplusNoise)isaveryimportantparameterbywhichallaudioamplifiersaremea-sured.Oftenitisshownasagraphwhereeithertheoutputpowerorfrequencyischangedovertheoperatingrange.AveryimportantvariableinthemeasurementofTHD+Nisthebandwidth-limitingfilterattheinputofthetestequipment.ClassDamplifiers,bydesign,switchtheiroutputpowerdevicesatamuchhigherfrequencythantheacceptedaudiorange(20Hz-20kHz).Alternatelyswitchingtheoutputvolt-agebetweenVDDandGNDallowstheLM4668tooperateatmuchhigherefficiencythanthatachievedbytraditionalClassABamplifiers.Switchingtheoutputsathighfrequencyalsoincreasestheout-of-bandnoise.Undernormalcircum-stancestheoutputlowpassfiltersignificantlyreducesthisout-of-bandnoise.Ifthelowpassfilterisnotoptimizedforagivenswitchingfrequency,therecanbesignificantincreaseinout-of-bandnoise.THD+Nmeasurementscanbesignifi-cantlyaffectedbyout-of-bandnoise,resultinginahigherthanexpectedTHD+Nmeasurement.ToachieveamoreaccuratemeasurementofTHD,thetestequipment’sinputbandwidthofthemustbelimited.Somecommonupperfilterpointsare22kHz,30kHz,and80kHz.TheinputfilterlimitsthenoisecomponentoftheTHD+Nmeasurementtoasmallerbandwidthresultinginamorereal-worldTHD+Nvalue.

RECOMMENDEDPRINTEDCIRCUITBOARDLAYOUTFigures2through4showtherecommendedtwo-layerPCboardlayoutthatisoptimizedforthe14-pinMH-packagedLM4668andassociatedexternalcomponents.Figures5through7showtherecommendedtwo-layerPCboardlay-outthatisoptimizedforthe14-pinLD-packagedLM4668andassociatedexternalcomponents.Thesecircuitsarede-signedforusewithanexternal12Vsupplyand8Ωspeakers(orloadresistors).Thiscircuitboardiseasytouse.Apply12Vandgroundtotheboard’sVDDandGNDterminals,respectively.Connectspeakers(orloadresistors)betweentheboard’s-OUTand+OUTterminals.Applytheinputsignaltotheinputpinlabeled-IN.

nominalcutofffrequencyof47kHz.Thiscutofffrequencyensuresthattheattenuationismuchlessthan3dBat20kHz.Theoutputfiltercutofffrequencyandtopologyarealsooptimizedforoperationalefficiency.Ahighercutofffrequencycompromisesefficiency,whereasalowercutofffrequencycompromisesthehighfrequencieswithintheaudiofre-quencyrange.Thefilter’stopologyalsominimizeshighfre-quencypeaking,whichcanalsodecreasetheamplifier’sefficiency.

Theoutputfilterinductorsmusthaveacurrentratingthatexceedstheamplifier’soutputcurrentwhendrivingtheloadtomaximumdissipation.Assumingaloaddissipationof10Winan8Ωloadwiththeamplifieroperatingona14Vsupply,theRMScurrentis1.1A.Inthiscase,theinductors’currentratingshouldbeatleast1.2ARMSor1.6APEAK.

Ifadifferentoutputfiltercutofffrequency(fC)isdesired,thefollowingbriefdiscussioncoverstheselectionofthecapaci-torandinductorvalues.Inthefollowingequations,RListheloadresistanceandCListhreetimesthefinalvalueofthethreecommon-modefiltercapacitorfoundbetweenthetwooutputfilterinductors(eachinductorisL)asshowninFigure1.WhencalculatingvaluesforLandCL,RLshouldbe8Ω,sincetheLM4668isspecifiedfor8Ωloads.Thefilter’stwoinductorsareequalto

L=RL/2πfCandeachofthethreecapacitorsareequalto

C=L/1.5R2(2)(1)

SCHOTTKYDIODEAMPLIFIEROUTPUTOVERDRIVEPROTECTION

TheSchottkydiodesshowninFigure1provideprotectionagainstanover-voltageconditionthatmaybecausedbyinductor-inducedtransients.Thesediodesarenecessarywhenthenominalsupplyvoltageexceeds12V,theloadimpedancefallsbelow6Ωortheambienttemperatureintheoperatingenvironmentrisesabove50˚C.

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LM4668DemonstrationBoardLayout

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FIGURE2.RecommendedMHPCBLayout

TopSilkscreen

20089104

FIGURE3.RecommendedMHPCBLayout

TopLayer

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LM4668DemonstrationBoardLayout

(Continued)

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FIGURE4.RecommendedMHPCBLayout

BottomLayer

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FIGURE5.RecommendedLDPCBLayout

TopSilkscreenLayer

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LM4668DemonstrationBoardLayout

(Continued)

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FIGURE6.RecommendedLDPCBLayout

TopLayer

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FIGURE7.RecommendedLDPCBLayout

BottomLayer

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LM4668PhysicalDimensions

unlessotherwisenoted

inches(millimeters)

LDPackage

OrderNumberLM4668LDNSPackageNumberLDC14A

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LM466810WHigh-EfficiencyMonoBTLAudioPowerAmplifierPhysicalDimensions

inches(millimeters)unlessotherwisenoted(Continued)

MHPackage

OrderNumberLM4668MHNSPackageNumberMXA20A

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