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LM4910

FEATURES

•

Eliminatesheadphoneamplifieroutputcouplingcapacitors

Eliminateshalf-supplybypasscapacitorAdvancedpop&clickcircuitryeliminatesnoisesduringturn-onandturn-offUltra-lowcurrentshutdownmodeUnity-gainstable2.2V-5.5Voperation

OutputCapacitor-lessStereo35mWHeadphoneAmplifier

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•

Availableinspace-savingMSOP,LLP,andSOICpackages

•••••

APPLICATIONS

••••

MobilePhonesPDAs

PortableelectronicsdevicesPortableMP3players

DESCRIPTION

TheLM4910isanaudiopoweramplifierprimarilydesignedforheadphoneapplicationsinportabledeviceapplications.Itiscapableofdelivering35mWofcontinuousaveragepowertoa32Ωloadwithlessthan1%distortion(THD+N)froma3.3VDCpowersupply.

TheLM4910utilizesanewcircuittopologythateliminatesoutputcouplingcapacitorsandhalf-supplybypasscapacitors.TheLM4910containsadvancedpop&clickcircuitrywhicheliminatesnoisescausedbytransientsthatwouldotherwiseoccurduringturn-onandturn-off.

Boomeraudiopoweramplifiersweredesignedspecificallytoprovidehighqualityoutputpowerwithaminimalamountofexternalcomponents.SincetheLM4910doesnotrequireanyoutputcouplingcapacitors,half-supplybypasscapacitors,orbootstrapcapacitors,itisideallysuitedforlow-powerportableapplicationswhereminimalspaceandpowerconsumptionareprimaryrequirements.

TheLM4910featuresalow-powerconsumptionshutdownmode,activatedbydrivingtheshutdownpinwithlogiclow.Additionally,theLM4910featuresaninternalthermalshutdownprotectionmechanism.TheLM4910isalsounity-gainstableandcanbeconfiguredbyexternalgain-settingresistors.

Table1.KeySpecifications

VALUE

PSRRatf=217Hz

PowerOutputatVDD=3.3V,RL=32Ω,andTHD≤1%ShutdownCurrent

65350.1

UNITdB(typ)mW(typ)µA(typ)

Pleasebeawarethatanimportantnoticeconcerningavailability,standardwarranty,anduseincriticalapplicationsofTexasInstrumentssemiconductorproductsanddisclaimerstheretoappearsattheendofthisdatasheet.

Alltrademarksarethepropertyoftheirrespectiveowners.

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PRODUCTIONDATAinformationiscurrentasofpublicationdate.ProductsconformtospecificationsperthetermsoftheTexasInstrumentsstandardwarranty.Productionprocessingdoesnotnecessarilyincludetestingofallparameters.

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TypicalApplication

Figure1.TypicalAudioAmplifierApplicationCircuit

ConnectionDiagram

Figure2.MSOP/SOPackageTopView

Figure3.MSOPMarkingTopView

G-BoomerFamilyC2-LM4910MM

Figure4.SOMarkingTopView

TT-DieTraceability

Bottom2lines-PartNumber

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Figure5.LLPPackageTopView

Thesedeviceshavelimitedbuilt-inESDprotection.TheleadsshouldbeshortedtogetherorthedeviceplacedinconductivefoamduringstorageorhandlingtopreventelectrostaticdamagetotheMOSgates.

AbsoluteMaximumRatings

SupplyVoltageInputVoltagePowerDissipationESDSusceptibilityESDSusceptibility

(3)

(4)

(2)

(1)

6.0V

−65°Cto+150°C-0.3VtoVDD+0.3VInternallyLimited

10kV2000V200V150°C56°C/W190°C/W35°C/W150°C/W57°C/W140°C/W

StorageTemperature

ESDSusceptibilityPin6

(5)(6)

JunctionTemperatureThermalResistanceθJC(MSOP)θJA(MSOP)θJC(SOP)θJA(SOP)θJC(LQ)θJA(LQ)(1)

(2)(3)(4)(5)(6)

AbsoluteMaximumRatingsindicatelimitsbeyondwhichdamagetothedevicemayoccur.OperatingRatingsindicateconditionsforwhichthedeviceisfunctionalbutdonotguaranteespecificperformancelimits.ElectricalCharacteristicsstateDCandACelectricalspecificationsunderparticulartestconditionswhichguaranteespecificperformancelimits.ThisassumesthatthedeviceiswithintheOperatingRatings.Specificationsarenotguaranteedforparameterswherenolimitisgiven,however,thetypicalvalueisagoodindicationofdeviceperformance.

IftheproductisinshutdownmodeandVDDexceeds6V(toamaxof8VVDD)thenmostoftheexcesscurrentwillflowthroughtheESDprotectioncircuits.Ifthesourceimpedancelimitsthecurrenttoamaxof10mathenthepartwillbeprotected.IfthepartisenabledwhenVDDisabove6Vcircuitperformancewillbecurtailedorthepartmaybepermanentlydamaged.

ThemaximumpowerdissipationmustbederatedatelevatedtemperaturesandisdictatedbyTJMAX,θJA,andtheambienttemperature,TA.ThemaximumallowablepowerdissipationisPDMAX=(TJMAX-TA)/θJAorthenumbergiveninAbsoluteMaximumRatings,whicheverislower.FortheLM4910,seepowerderatingcurrentsformoreinformation.Humanbodymodel,100pFdischargedthrougha1.5kΩresistor,Pin6toground.Humanbodymodel,100pFdischargedthrougha1.5kΩresistor.MachineModel,220pF-240pFdischargedthroughallpins.

OperatingRatings

TemperatureRangeTMIN≤TA≤TMAXSupplyVoltage(VDD)

−40°C≤TA≤85°C2.2V≤VCC≤5.5V

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(1)(2)

ElectricalCharacteristicsVDD=3.3V

Symbol

Parameter

ThefollowingspecificationsapplyforVDD=3.3V,AV=1,and32Ωloadunlessotherwisespecified.LimitsapplytoTA=25°C.

Conditions

Typ

(3)

LM4910

Limit

(4)(5)

Units(Limits)mA(max)µA(max)mV(max)mW(min)

%dB

IDDISDVOSPOTHD+NPSRRVIHVIL(1)(2)

QuiescentPowerSupplyCurrentStandbyCurrentOutputOffsetVoltageOutputPower

TotalHarmonicDistortion+NoisePowerSupplyRejectionRatioShutdownInputVoltageHighShutdownInputVoltageLow

VIN=0V,32ΩLoadVSHUTDOWN=GNDTHD=1%(max);f=1kHzPO=30mWrms;f=1kHz

VRIPPLE=200mVp-psinewave

Inputterminatedwith10Ωtoground

3.50.15350.365(f=217Hz)65(f=1kHz)

61.03030

1.50.4

V(min)V(max)

(3)(4)(5)

AllvoltagesaremeasuredwithrespecttotheGNDpinunlessotherwisespecified.

AbsoluteMaximumRatingsindicatelimitsbeyondwhichdamagetothedevicemayoccur.OperatingRatingsindicateconditionsforwhichthedeviceisfunctionalbutdonotguaranteespecificperformancelimits.ElectricalCharacteristicsstateDCandACelectricalspecificationsunderparticulartestconditionswhichguaranteespecificperformancelimits.ThisassumesthatthedeviceiswithintheOperatingRatings.Specificationsarenotguaranteedforparameterswherenolimitisgiven,however,thetypicalvalueisagoodindicationofdeviceperformance.

Typicalsaremeasuredat25°Candrepresenttheparametricnorm.

LimitsareguaranteedtoNational'sAOQL(AverageOutgoingQualityLevel).

Datasheetmin/maxspecificationlimitsareguaranteedbydesign,test,orstatisticalanalysis.

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(1)(2)

ElectricalCharacteristicsVDD=3V

Symbol

Parameter

ThefollowingspecificationsapplyforVDD=3V,AV=1,and32Ωloadunlessotherwisespecified.LimitsapplytoTA=25°C.

Conditions

Typ

(3)

LM4910

Limit

(4)(5)

Units(Limits)mA(max)µA(max)mV(max)mW(min)

%dB

IDDISDVOSPOTHD+NPSRRVIHVIL(1)(2)

QuiescentPowerSupplyCurrentStandbyCurrentOutputOffsetVoltageOutputPower

TotalHarmonicDistortion+NoisePowerSupplyRejectionRatioShutdownInputVoltageHighShutdownInputVoltageLow

VIN=0V,32ΩLoadVSHUTDOWN=GNDTHD=1%(max);f=1kHzPO=25mWrms;f=1kHz

VRIPPLE=200mVp-psinewave

Inputterminatedwith10Ωtoground

3.30.15300.365(f=217

Hz)65(f=1kHz)

61.03025

1.50.4

V(min)V(max)

(3)(4)(5)

AllvoltagesaremeasuredwithrespecttotheGNDpinunlessotherwisespecified.

AbsoluteMaximumRatingsindicatelimitsbeyondwhichdamagetothedevicemayoccur.OperatingRatingsindicateconditionsforwhichthedeviceisfunctionalbutdonotguaranteespecificperformancelimits.ElectricalCharacteristicsstateDCandACelectricalspecificationsunderparticulartestconditionswhichguaranteespecificperformancelimits.ThisassumesthatthedeviceiswithintheOperatingRatings.Specificationsarenotguaranteedforparameterswherenolimitisgiven,however,thetypicalvalueisagoodindicationofdeviceperformance.

Typicalsaremeasuredat25°Candrepresenttheparametricnorm.

LimitsareguaranteedtoNational'sAOQL(AverageOutgoingQualityLevel).

Datasheetmin/maxspecificationlimitsareguaranteedbydesign,test,orstatisticalanalysis.

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(1)(2)

ElectricalCharacteristicsVDD=2.6V

Symbol

Parameter

ThefollowingspecificationsapplyforVDD=2.6V,AV=1,and32Ωloadunlessotherwisespecified.LimitsapplytoTA=25°C.

Conditions

Typ

(3)

LM4910

Limit

(4)(5)

Units(Limits)mA(max)µA(max)mV(max)mW%dB

IDDISDVOSPOTHD+NPSRR

QuiescentPowerSupplyCurrentStandbyCurrentOutputOffsetVoltageOutputPower

TotalHarmonicDistortion+NoisePowerSupplyRejectionRatio

VIN=0V,32ΩLoadVSHUTDOWN=GNDTHD=1%(max);f=1kHzPO=10mWrms;f=1kHz

VRIPPLE=200mVp-psinewave

Inputterminatedwith10Ωtoground

3.00.15130.355(f=217Hz)55(f=1kHz)

(1)(2)

(3)(4)(5)

AllvoltagesaremeasuredwithrespecttotheGNDpinunlessotherwisespecified.

AbsoluteMaximumRatingsindicatelimitsbeyondwhichdamagetothedevicemayoccur.OperatingRatingsindicateconditionsforwhichthedeviceisfunctionalbutdonotguaranteespecificperformancelimits.ElectricalCharacteristicsstateDCandACelectricalspecificationsunderparticulartestconditionswhichguaranteespecificperformancelimits.ThisassumesthatthedeviceiswithintheOperatingRatings.Specificationsarenotguaranteedforparameterswherenolimitisgiven,however,thetypicalvalueisagoodindicationofdeviceperformance.

Typicalsaremeasuredat25°Candrepresenttheparametricnorm.

LimitsareguaranteedtoNational'sAOQL(AverageOutgoingQualityLevel).

Datasheetmin/maxspecificationlimitsareguaranteedbydesign,test,orstatisticalanalysis.

ExternalComponentsDescription

(Figure1)

Components1.2.

RICI

FunctionalDescription

Invertinginputresistancewhichsetstheclosed-loopgaininconjunctionwithRf.Thisresistoralsoformsahigh-passfilterwithCiatfc=1/(2πRiCi).

InputcouplingcapacitorwhichblockstheDCvoltageattheamplifier'sinputterminals.Alsocreatesahigh-passfilterwithRiatfc=1/(2πRiCi).RefertothesectionProperSelectionofExternalComponents,foranexplanationofhowtodeterminethevalueofCi.

Feedbackresistancewhichsetstheclosed-loopgaininconjunctionwithRi.

Supplybypasscapacitorwhichprovidespowersupplyfiltering.RefertothePowerSupplyBypassingsectionforinformationconcerningproperplacementandselectionofthesupplybypasscapacitor.

3.4.

RfCS

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TypicalPerformanceCharacteristics

THD+NvsFrequency

THD+NvsFrequency

THD+NvsFrequencyTHD+NvsFrequency

THD+NvsFrequencyTHD+NvsFrequency

THD+Nvs

OutputPowerTHD+Nvs

OutputPower

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TypicalPerformanceCharacteristics(continued)

THD+Nvs

OutputPower

THD+Nvs

OutputPower

THD+Nvs

OutputPowerTHD+Nvs

OutputPower

OutputPower

vs

LoadResistance

OutputPowervsLoadResistance

OutputPowervsLoadResistanceOutputPowervsSupplyVoltage

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TypicalPerformanceCharacteristics(continued)

OutputPowervsSupplyVoltage

PowerDissipationvs

OutputPower

PowerDissipationvs

OutputPowerPowerDissipationvs

OutputPower

ChannelSeparationPowerSupplyRejectionRatio

PowerSupplyRejectionRatioPowerSupplyRejectionRatio

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TypicalPerformanceCharacteristics(continued)

OpenLoopFrequencyResponse

NoiseFloor

FrequencyResponsevsInputCapacitorSizeSupplyCurrentvsSupplyVoltage

ApplicationInformation

ELIMINATINGOUTPUTCOUPLINGCAPACITORS

Typicalsingle-supplyaudioamplifiersthatdrivesingle-ended(SE)headphonesuseacouplingcapacitoroneachSEoutput.Thisoutputcouplingcapacitorblocksthehalf-supplyvoltagetowhichtheoutputamplifiersaretypicallybiasedandcouplestheaudiosignaltotheheadphones.Thesignalreturntocircuitgroundisthroughtheheadphonejack'ssleeve.

TheLM4910eliminatestheseoutputcouplingcapacitors.Amp3isinternallyconfiguredtoapplyabandgapreferencedvoltage(VREF=1.58V)toastereoheadphonejack'ssleeve.ThisvoltagematchesthequiescentvoltagepresentontheAmp1andAmp2outputsthatdrivetheheadphones.Theheadphonesoperateinamannersimilartoabridge-tied-load(BTL).ThesameDCvoltageisappliedtobothheadphonespeakerterminals.ThisresultsinnonetDCcurrentflowthroughthespeaker.ACcurrentflowsthroughaheadphonespeakerasanaudiosignal'soutputamplitudeincreasesonthespeaker'sterminal.

Theheadphonejack'ssleeveisnotconnectedtocircuitground.Usingtheheadphoneoutputjackasaline-leveloutputwillplacetheLM4910'sbandgapreferencedvoltageonaplug'ssleeveconnection.Thispresentsnodifficultywhentheexternalequipmentusescapacitivelycoupledinputs.FortheverysmallminorityofequipmentthatisDC-coupled,theLM4910monitorsthecurrentsuppliedbytheamplifierthatdrivestheheadphonejack'ssleeve.Ifthiscurrentexceeds500mAPK,theamplifierisshutdown,protectingtheLM4910andtheexternalequipment.

ELIMINATINGTHEHALF-SUPPLYBYPASSCAPACITOR

Typicalsingle-supplyaudioamplifersarenormallybiasedto1/2VDDinordertomaximizetheoutputswingoftheaudiosignal.ThisisusuallyachievedwithasimpleresistordividernetworkfromVDDtogroundthatprovidestheproperbiasvoltagetotheamplifier.However,thisschemerequirestheuseofahalf-supplybypasscapacitortoimprovethebiasvoltage'sstabilityandtheamplifier'sPSRRperformance.

TheLM4910utilizesaninternallygenerated,bufferedbandgapreferencevoltageastheamplifier'sbiasvoltage.ThisbandgapreferencevoltageisnotadirectfunctionofVDDandthereforeislesssusceptibletonoiseorrippleonthepowersupplyline.ThisallowsfortheLM4910tohaveastablebiasvoltageandexcellentPSRRperformanceevenwithoutahalf-supplybypasscapacitor.

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OUTPUTTRANSIENT('CLICKANDPOPS')ELIMINATED

TheLM4910containsadvancedcircuitrythatvirtuallyeliminatesoutputtransients('clicksandpops').Thiscircuitrypreventsalltracesoftransientswhenthesupplyvoltageisfirstappliedorwhenthepartresumesoperationaftercomingoutofshutdownmode.TheLM4910remainsinamutedconditionuntilthereissufficientinputsignalmagnitude(>5mVRMS,typ)tomaskanyremainingtransientthatmayoccur.Figure2showstheLM4910'slackoftransientsinthedifferentialsignal(TraceB)acrossa320load.TheLM4910'sactive-lowSHUTDOWNpinisdrivenbythelogicsignalshowninTraceA.TraceCistheVO1outputsignalandTraceDistheVO3outputsignal.

Toensureoptimalclickandpopperformanceunderlowgainconfigurations(lessthan0dB),itiscriticaltominimizetheRCcombinationofthefeedbackresistorRFandstrayinputcapacitanceattheamplifierinputs.AmorereliablewaytolowergainorreducepowerdeliveredtotheloadistoplaceacurrentlimitingresistorinserieswiththeloadasexplainedintheMinimizingOutputNoise/ReducingOutputPowersection.

AMPLIFIERCONFIGURATIONEXPLANATION

AsshowninFigure1,theLM4910hasthreeoperationalamplifiersinternally.Twooftheamplifier'shaveexternallyconfigurablegainwhiletheotheramplifierisinternallyfixedatthebiaspointactingasaunity-gainbuffer.Theclosed-loopgainofthetwoconfigurableamplifiersissetbyselectingtheratioofRftoRi.Consequently,thegainforeachchanneloftheICis

AV=-(Rf/Ri)

(1)

BydrivingtheloadsthroughoutputsVO1andVO2withVO3actingasabufferedbiasvoltagetheLM4910doesnotrequireoutputcouplingcapacitors.Thetypicalsingle-endedamplifierconfigurationwhereonesideoftheloadisconnectedtogroundrequireslarge,expensiveoutputcouplingcapacitors.

AconfigurationsuchastheoneusedintheLM4910hasamajoradvantageoversinglesupply,single-endedamplifiers.SincetheoutputsVO1,VO2,andVO3areallbiasedatVREF=1.58V,nonetDCvoltageexistsacrosseachload.Thiseliminatestheneedforoutputcouplingcapacitorsthatarerequiredinasingle-supply,single-endedamplifierconfiguration.Withoutoutputcouplingcapacitorsinatypicalsingle-supply,single-endedamplifier,thebiasvoltageisplacedacrosstheloadresultinginbothincreasedinternalICpowerdissipationandpossibleloudspeakerdamage.POWERDISSIPATION

Powerdissipationisamajorconcernwhendesigningasuccessfulamplifier.Adirectconsequenceoftheincreasedpowerdeliveredtotheloadbyabridgeamplifierisanincreaseininternalpowerdissipation.ThemaximumpowerdissipationforagivenapplicationcanbederivedfromthepowerdissipationgraphsorfromEquation1.

PDMAX=4(VDD)2/(π2RL)

(2)

ItiscriticalthatthemaximumjunctiontemperatureTJMAXof150°Cisnotexceeded.Sincethetypicalapplicationisforheadphoneoperation(32Ωimpedance)usinga3.3Vsupplythemaximumpowerdissipationisonly138mW.Therefore,powerdissipationisnotamajorconcern.

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POWERSUPPLYBYPASSING

Aswithanyamplifier,propersupplybypassingisimportantforlownoiseperformanceandhighpowersupplyrejection.Thecapacitorlocationonthepowersupplypinsshouldbeasclosetothedeviceaspossible.

Typicalapplicationsemploya3.3Vregulatorwith10µFtantalumorelectrolyticcapacitorandaceramicbypasscapacitorwhichaidinsupplystability.ThisdoesnoteliminatetheneedforbypassingthesupplynodesoftheLM4910.Abypasscapacitorvalueintherangeof0.1µFto1µFisrecommendedforCS.MICROPOWERSHUTDOWN

ThevoltageappliedtotheSHUTDOWNpincontrolstheLM4910'sshutdownfunction.Activatemicro-powershutdownbyapplyingalogic-lowvoltagetotheSHUTDOWNpin.Whenactive,theLM4910'smicro-powershutdownfeatureturnsofftheamplifier'sbiascircuitry,reducingthesupplycurrent.Thetriggerpointis0.4V(max)foralogic-lowlevel,and1.5V(min)foralogic-highlevel.Thelow0.1µA(typ)shutdowncurrentisachievedbyapplyingavoltagethatisasnearasgroundaspossibletotheSHUTDOWNpin.Avoltagethatishigherthangroundmayincreasetheshutdowncurrent.

Thereareafewwaystocontrolthemicro-powershutdown.Theseincludeusingasingle-pole,single-throwswitch,amicroprocessor,oramicrocontroller.Whenusingaswitch,connectanexternal100kΩpull-upresistorbetweentheSHUTDOWNpinandVDD.ConnecttheswitchbetweentheSHUTDOWNpinandground.Selectnormalamplifieroperationbyopeningtheswitch.ClosingtheswitchconnectstheSHUTDOWNpintoground,activatingmicro-powershutdown.TheswitchandresistorguaranteethattheSHUTDOWNpinwillnotfloat.Thispreventsunwantedstatechanges.Inasystemwithamicroprocessorormicrocontroller,useadigitaloutputtoapplythecontrolvoltagetotheSHUTDOWNpin.DrivingtheSHUTDOWNpinwithactivecircuitryeliminatesthepull-upresistor.

SELECTINGEXTERNALCOMPONENTS

Selectingproperexternalcomponentsinapplicationsusingintegratedpoweramplifiersiscriticaltooptimizedeviceandsystemperformance.WhiletheLM4910istolerantofexternalcomponentcombinations,considerationtocomponentvaluesmustbeusedtomaximizeoverallsystemquality.

TheLM4910isunity-gainstablewhichgivesthedesignermaximumsystemflexibility.TheLM4910shouldbeusedinlowgainconfigurationstominimizeTHD+Nvalues,andmaximizethesignaltonoiseratio.Lowgainconfigurationsrequirelargeinputsignalstoobtainagivenoutputpower.Inputsignalsequaltoorgreaterthan1Vrmsareavailablefromsourcessuchasaudiocodecs.Verylargevaluesshouldnotbeusedforthegain-settingresistors.ValuesforRiandRfshouldbelessthan1MΩ.Pleaserefertothesection,AudioPowerAmplifierDesign,foramorecompleteexplanationofpropergainselection

Besidesgain,oneofthemajorconsiderationsistheclosed-loopbandwidthoftheamplifier.Toalargeextent,thebandwidthisdictatedbythechoiceofexternalcomponentsshowninFigure1.Theinputcouplingcapacitor,Ci,formsafirstorderhighpassfilterwhichlimitslowfrequencyresponse.Thisvalueshouldbechosenbasedonneededfrequencyresponseandturn-ontime.SELECTIONOFINPUTCAPACITORSIZE

Amplifiyingthelowestaudiofrequenciesrequiresahighvalueinputcouplingcapacitor,Ci.Ahighvaluecapacitorcanbeexpensiveandmaycompromisespaceefficiencyinportabledesigns.Inmanycases,however,theheadphonesusedinportablesystemshavelittleabilitytoreproducesignalsbelow60Hz.Applicationsusingheadphoneswiththislimitedfrequencyresponsereaplittleimprovementbyusingahighvalueinputcapacitor.Inadditiontosystemcostandsize,turn-ontimeisaffectedbythesizeoftheinputcouplingcapacitorCi.AlargerinputcouplingcapacitorrequiresmorechargetoreachitsquiescentDCvoltage.ThischargecomesfromtheoutputviathefeedbackThus,byminimizingthecapacitorsizebasedonnecessarylowfrequencyresponse,turn-ontimecanbeminimized.AsmallvalueofCi(intherangeof0.1µFto0.39µF),isrecommended.

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USINGEXTERNALPOWEREDSPEAKERS

TheLM4910isdesignedspecificallyforheadphoneoperation.Oftentheheadphoneoutputofadevicewillbeusedtodriveexternalpoweredspeakers.TheLM4910hasadifferentialoutputtoeliminatetheoutputcouplingcapacitors.TheresultisaheadphonejacksleevethatisconnectedtoVO3insteadofGND.Forpoweredspeakersthataredesignedtohavesingle-endedsignalsattheinput,theclickandpopcircuitrywillnotbeabletoeliminatetheturn-on/turn-offclickandpop.Unlesstheinputstothepoweredspeakersarefullydifferentialtheturn-on/turn-offclickandpopwillbeverylarge.AUDIOPOWERAMPLIFIERDESIGNA30mW/32ΩAudioAmplifier

Given:PowerOutputLoadImpedanceInputLevelInputImpedance

30mWrms

32Ω1Vrms20kΩ

Adesignermustfirstdeterminetheminimumsupplyrailtoobtainthespecifiedoutputpower.ByextrapolatingfromtheOutputPowervsSupplyVoltagegraphsintheTypicalPerformanceCharacteristicssection,thesupplyrailcanbeeasilyfound.

Since3.3Visastandardsupplyvoltageinmostapplications,itischosenforthesupplyrailinthisexample.ExtrasupplyvoltagecreatesheadroomthatallowstheLM4910toreproducepeaksinexcessof30mWwithoutproducingaudibledistortion.Atthistime,thedesignermustmakesurethatthepowersupplychoicealongwiththeoutputimpedancedoesnoviolatetheconditionsexplainedinthePowerDissipationsection.

Oncethepowerdissipationequationshavebeenaddressed,therequireddifferentialgaincanbedeterminedfromEquation2.

(3)

FromEquation2,theminimumAVis0.98;useAV=1.Sincethedesiredinputimpedanceis20kΩ,andwithAVequalto1,aratioof1:1resultsfromEquation1forRftoRi.ThevaluesarechosenwithRi=20kΩandRf=20kΩ.

Thelaststepinthisdesignexampleissettingtheamplifier's−3dBfrequencybandwidth.Toachievethedesired±0.25dBpassbandmagnitudevariationlimit,thelowfrequencyresponsemustextendtoatleastone-fifththelowerbandwidthlimitandthehighfrequencyresponsemustextendtoatleastfivetimestheupperbandwidthlimit.Thegainvariationforbothresponselimitsis0.17dB,wellwithinthe±0.25dBdesiredlimit.Theresultsarean

fL=100Hz/5=20Hz

(4)(5)

andan

fH=20kHzx5=100kHz

AsmentionedintheSelectingProperExternalComponentssection,RiandCicreateahighpassfilterthatsetstheamplifier'slowerbandpassfrequencylimit.Findthecouplingcapacitor'svalueusingEquation(3).

Ci≥1/(2πRifL)

(6)

Theresultis

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1/(2π*20kΩ*20Hz)=0.397µF(7)

Usea0.39µFcapacitor,thecloseststandardvalue.

Thehighfrequencypoleisdeterminedbytheproductofthedesiredfrequencypole,fH,andthedifferentialgain,AV.WithanAV=1andfH=100kHz,theresultingGBWP=100kHzwhichismuchsmallerthantheLM4910GBWPof11MHz.Thisfiguredisplaysthatifadesignerhasaneedtodesignanamplifierwithhigherdifferentialgain,theLM4910canstillbeusedwithoutrunningintobandwidthlimitations.MINIMIZINGOUTPUTNOISE/REDUCINGOUTPUTPOWER

Figure6.

Outputnoisedeliveredtotheloadcanbeminimizedwiththeuseofanexternalresistor,RSERIES,placedinserieswitheachloadasshowninFigure6.RSERIESformsavoltagedividerwiththeimpedanceoftheheadphonedriverRL.Asaresult,outputnoiseisattenuatedbythefactorRL/(RL+RSERIES).Figure7illustratestherelationshipbetweenoutputnoiseandRSERIESfordifferentloads.RSERIESalsodecreasesoutputpowerdeliveredtotheloadbythefactorRL/(RL+RSERIES)2.However,thismaynotposeaproblemsincemostheadphoneapplicationsrequirelessthan10mWofoutputpower.Figure9illustratesoutputpower(@1%THD+N)vsRSERIESfordifferentloads.

Figure7showsanoptionalresistorconnectedbetweentheamplifieroutputthatdrivestheheadphonejacksleeveandground.Thisresistorprovidesagroundpaththatsupressedpowersupplyhum.Thishummayoccurinapplicationssuchasnotebookcomputersinashutdownconditionandconnectedtoanexternalpoweredspeaker.Theresistor's100Ωvalueisasuggestedstartingpoint.Itsfinalvaluemustbedeterminedbasedonthetradeoffbetweentheamountofnoisesuppressionthatmaybeneededandminimizingtheadditionalcurrentdrawnbytheresistor(25mAfora100Ωresistoranda5Vsupply).ESDPROTECTION

AsstatedintheAbsoluteMaximumRatings,pin6(Vo3)ontheLM4910hasamaximumESDsusceptibilityratingof10kV.ForhigherESDvoltages,theadditionofaPCDN042dualtransil(fromCaliforniaMicroDevices),asshowninFigure7,willprovideadditionalprotection.

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Figure7.ThePCDN042providesadditionalESDprotectionbeyondthe10kVshownintheAbsolute

MaximumRatingsfortheVo3output

Figure8.OutputNoisevsRSERIES

Figure9.

Figure10.OutputPowervsRSERIES

Figure11.

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HIGHERGAINAUDIOAMPLIFIER

TheLM4910isunity-gainstableandrequiresnoexternalcomponentsbesidesgain-settingresistors,inputcouplingcapacitors,andpropersupplybypassinginthetypicalapplication.However,ifaverylargeclosed-loopdifferentialgainisrequired,afeedbackcapacitor(Cf)maybeneededasshowninFigure11tobandwidthlimittheamplifier.Thisfeedbackcapacitorcreatesalowpassfilterthateliminatespossiblehighfrequencyoscillations.Careshouldbetakenwhencalculatingthe-3dBfrequencyinthatanincorrectcombinationofRfandCfwillcausefrequencyresponserolloffbefore20kHz.AtypicalcombinationoffeedbackresistorandcapacitorthatwillnotproduceaudiobandhighfrequencyrolloffisRf=20kΩandCf=25pF.Thesecomponentsresultina-3dBpointofapproximately320kHz.

REFERENCEDESIGNBOARDandLAYOUTGUIDELINESMSOP&SOBOARDS

(Note:RPU2isnotrequired.Itisusedfortestmeasurementpurposesonly.)

16

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LM4910SODEMOBOARDARTWORK

Figure12.CompositeView

Figure13.SilkScreen

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Figure14.TopLayer

Figure15.BottomLayer

18SubmitDocumentationFeedback

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LM4910

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LM4910MSOPDEMOBOARDARTWORK

Figure16.CompositeView

Figure17.SilkScreen

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Figure18.TopLayer

Figure19.BottomLayer

20SubmitDocumentationFeedback

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LM4910LLPDEMOBOARDARTWORK

Figure20.CompositeView

Figure21.SilkScreen

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Figure22.TopLayer

Figure23.BottomLayer

LM4910ReferenceDesignBoardsBillofMaterials

PartDescription

LM4910MonoReferenceDesignBoard

LM4910AudioAMPTantalumCap1µF16V10CeramicCap0.39µF50VZ5020

Resistor20kΩ1/10W5Resistor100kΩ1/10W5

JumperHeaderVerticalMount2X1,0.100

Qty1112411

U1CsCiRi,RfRpuJ1

RefDesignator

PCBLAYOUTGUIDELINES

ThissectionprovidespracticalguidelinesformixedsignalPCBlayoutthatinvolvesvariousdigital/analogpowerandgroundtraces.Designersshouldnotethattheseareonly\"rule-of-thumb\"recommendationsandtheactualresultswilldependheavilyonthefinallayout.

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SNAS151G–MAY2004–REVISEDMARCH2007

MinimizationofTHD

PCBtraceimpedanceonthepower,ground,andalloutputtracesshouldbeminimizedtoachieveoptimalTHDperformance.Therefore,usePCBtracesthatareaswideaspossiblefortheseconnections.Asthegainoftheamplifierisincreased,thetraceimpedancewillhaveaneverincreasingadverseaffectonTHDperformance.Atunity-gain(0dB)theparasitictraceimpedanceeffectonTHDperformanceisreducedbutstillanegativefactorintheTHDperformanceoftheLM4910inagivenapplication.GENERALMIXEDSIGNALLAYOUTRECOMMENDATIONPowerandGroundCircuits

Fortwolayermixedsignaldesign,itisimportanttoisolatethedigitalpowerandgroundtracepathsfromtheanalogpowerandgroundtracepaths.Startraceroutingtechniques(bringingindividualtracesbacktoacentralpointratherthandaisychainingtracestogetherinaserialmanner)cangreatlyenhancelowlevelsignalperformance.Startraceroutingreferstousingindividualtracestofeedpowerandgroundtoeachcircuitorevendevice.Thistechniquewillrequireagreateramountofdesigntimebutwillnotincreasethefinalpriceoftheboard.Theonlyextrapartsrequiredmaybesomejumpers.Single-PointPower/GroundConnections

Theanalogpowertracesshouldbeconnectedtothedigitaltracesthroughasinglepoint(link).A\"PI-filter\"canbehelpfulinminimizinghighfrequencynoisecouplingbetweentheanaloganddigitalsections.Further,placedigitalandanalogpowertracesoverthecorrespondingdigitalandanaloggroundtracestominimizenoisecoupling.

PlacementofDigitalandAnalogComponents

Alldigitalcomponentsandhigh-speeddigitalsignaltracesshouldbelocatedasfarawayaspossiblefromanalogcomponentsandcircuittraces.

AvoidingTypicalDesign/LayoutProblems

Avoidgroundloopsorrunningdigitalandanalogtracesparalleltoeachother(side-by-side)onthesamePCBlayer.Whentracesmustcrossovereachotherdoitat90degrees.Runningdigitalandanalogtracesat90degreestoeachotherfromthetoptothebottomsideasmuchaspossiblewillminimizecapacitivenoisecouplingandcrosstalk.

RevisionHistory

Rev1.01.1

Date7/12/0501/16/07

DescriptionReleasedtotheWEB.

Deletedthephrase“patentpending”onpage

1.

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PACKAGE OPTION ADDENDUM

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24-Jan

PACKAGING INFORMATION

Orderable DeviceLM4910LQ/NOPBLM4910LQX/NOPBLM4910MM/NOPB (1)

Status(1)Package TypePackagePinsPackage QtyDrawingWQFNWQFNVSSOPNGPNGPDGK888100045001000Eco Plan(2)Lead/Ball FinishCU SNCU SNCU SNMSL Peak Temp(3)Op Temp (°C)-40 to 85-40 to 85-40 to 85Top-Side Markings(4)SamplesACTIVEACTIVEACTIVEGreen (RoHS& no Sb/Br)Green (RoHS& no Sb/Br)Green (RoHS& no Sb/Br)Level-3-260C-168 HRLevel-3-260C-168 HRLevel-1-260C-UNLIMGA4GA4GC2 The marketing status values are defined as follows:ACTIVE: Product device recommended for new designs.

LIFEBUY: TI has announced that the device will be discontinued, and a lifetime-buy period is in effect.

NRND: Not recommended for new designs. Device is in production to support existing customers, but TI does not recommend using this part in a new design.PREVIEW: Device has been announced but is not in production. Samples may or may not be available.OBSOLETE: TI has discontinued the production of the device.

(2)

Eco Plan - The planned eco-friendly classification: Pb-Free (RoHS), Pb-Free (RoHS Exempt), or Green (RoHS & no Sb/Br) - please check http://www.ti.com/productcontent for the latest availabilityinformation and additional product content details.

TBD: The Pb-Free/Green conversion plan has not been defined.

Pb-Free (RoHS): TI's terms \"Lead-Free\" or \"Pb-Free\" mean semiconductor products that are compatible with the current RoHS requirements for all 6 substances, including the requirement thatlead not exceed 0.1% by weight in homogeneous materials. Where designed to be soldered at high temperatures, TI Pb-Free products are suitable for use in specified lead-free processes.

Pb-Free (RoHS Exempt): This component has a RoHS exemption for either 1) lead-based flip-chip solder bumps used between the die and package, or 2) lead-based die adhesive used betweenthe die and leadframe. The component is otherwise considered Pb-Free (RoHS compatible) as defined above.

Green (RoHS & no Sb/Br): TI defines \"Green\" to mean Pb-Free (RoHS compatible), and free of Bromine (Br) and Antimony (Sb) based flame retardants (Br or Sb do not exceed 0.1% by weightin homogeneous material)

(3)

MSL, Peak Temp. -- The Moisture Sensitivity Level rating according to the JEDEC industry standard classifications, and peak solder temperature. Only one of markings shown within the brackets will appear on the physical device.

(4)

Important Information and Disclaimer:The information provided on this page represents TI's knowledge and belief as of the date that it is provided. TI bases its knowledge and belief on informationprovided by third parties, and makes no representation or warranty as to the accuracy of such information. Efforts are underway to better integrate information from third parties. TI has taken andcontinues to take reasonable steps to provide representative and accurate information but may not have conducted destructive testing or chemical analysis on incoming materials and chemicals.TI and TI suppliers consider certain information to be proprietary, and thus CAS numbers and other limited information may not be available for release.

In no event shall TI's liability arising out of such information exceed the total purchase price of the TI part(s) at issue in this document sold by TI to Customer on an annual basis.

Addendum-Page 1

PACKAGEMATERIALSINFORMATION

www.ti.com

21-Mar-2013

TAPEANDREELINFORMATION

*Alldimensionsarenominal

Device

PackagePackagePinsTypeDrawingWQFNWQFNVSSOP

NGPNGPDGK

888

SPQ

ReelReelA0DiameterWidth(mm)(mm)W1(mm)178.0330.0178.0

12.412.412.4

2.22.25.3

B0(mm)2.22.23.4

K0(mm)1.01.01.4

P1(mm)8.08.08.0

WPin1(mm)Quadrant12.012.012.0

Q1Q1Q1

LM4910LQ/NOPBLM4910LQX/NOPBLM4910MM/NOPB

100045001000

PackMaterials-Page1

PACKAGEMATERIALSINFORMATION

www.ti.com

21-Mar-2013

*Alldimensionsarenominal

DeviceLM4910LQ/NOPBLM4910LQX/NOPBLM4910MM/NOPB

PackageType

WQFNWQFNVSSOP

PackageDrawing

NGPNGPDGK

Pins888

SPQ100045001000

Length(mm)

213.0358.0210.0

Width(mm)191.0343.0185.0

Height(mm)

55.063.035.0

PackMaterials-Page2

MECHANICAL DATA

NGP0008A

LQB08A (Rev B)www.ti.com

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Insomecases,TIcomponentsmaybepromotedspecificallytofacilitatesafety-relatedapplications.Withsuchcomponents,TI’sgoalistohelpenablecustomerstodesignandcreatetheirownend-productsolutionsthatmeetapplicablefunctionalsafetystandardsandrequirements.Nonetheless,suchcomponentsaresubjecttotheseterms.

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TIhasspecificallydesignatedcertaincomponentsasmeetingISO/TS16949requirements,mainlyforautomotiveuse.Inanycaseofuseofnon-designatedproducts,TIwillnotberesponsibleforanyfailuretomeetISO/TS16949.ProductsAudioAmplifiersDataConvertersDLP®ProductsDSP

ClocksandTimersInterfaceLogicPowerMgmtMicrocontrollersRFID

OMAPApplicationsProcessorsWirelessConnectivity

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