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AN-1490LM4702 Power Amplifier - TI.com

Application Information www.ti.com The LM4702 demonstration amplifier uses 0.5Ωdegeneration resistors in the emitter circuits of the Darlington transistors used in ...

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Text of AN-1490LM4702 Power Amplifier - TI.com

ApplicationReportSNAA031A May2006 + (BOM)................................... ........................................ ......................... , , , +NvsOutputPowerRL= 8 , Vsupply= May2006 RevisedMay2013AN-1490LM4702PowerAmplifie rSubmitDocumentationFeedbackCopyright 2006 2013, anamplifierthatmeasureswellin theuniversallyacceptedkeyparameterssucha sTHD+N( ),SNR,frequencyresponse, ,thesetechniqueswillalsoassistthedesigne rin creatinganaudioamplifierthathasperforman cecomparabletootheramplifiers, May2006 RevisedMay2013SubmitDocumentationFeedbac kCopyright 2006 2013, May2006 RevisedMay2013AN-1490LM4702PowerAmplifie rSubmitDocumentationFeedbackCopyright 2006 2013, ,highqualitycircuitboardlayouts, goodplacetostartis starconnectionis wherethereareindividualtracesfromeachcom ponentin thecircuitthatreturntoa goodexampleofthiscanbeseenin theartworkfortheLM4702demonstrationboard showninFigure2. Noticehowallthegroundtracesconvergeatthe leftsideoftheboard,nearRs1andRs2,andconn ecttothetwogroundpinsin theyarenotkeptseparate,thenthehighcurren tbeingdrawnbytheoutputstagecanaffect,ore venmodulate, groundplaneis a largeareaofcoppercommonlyusedin highfidelityamplifier,thiswillcreateconf usinggroundpaths(groundloops) veryaudiblehumis PCBwithseparategroundtracesandpowersuppl ytracesrequiresextralayoutdesigntime, theboardis kepttoa twolayersdesigninsteadofmulti-layerdesig ns,commonin therightandleftchannelareasofthePCBartwo rkis mirrorimageofthelefttotherightsidesofthe artworkonthecircuitboardcreatetheproperb alanced(identicalleftandrightchannel) +Nfortherightandleftchannelcircuits,theg roundconnectionsontheboardhadtobeidentic alin (.25mm) + mediocrelayoutoronewhichis morespecificpointabouttheLM4702demonstra tionboardartworktonoticeis onthetoplayeroftheamplifiercircuitboardw herea traceis connectedtoSink1 onpin3 oftheLM4702thatheadsofftotheoutputDarlin gtonTransistorsanda secondtraceis connectedtoSink2 wasdiscoveredthatthesetwotracesrequirea ( ) becausethisis ( ) May2006 RevisedMay2013SubmitDocumentationFeedbac kCopyright 2006 2013, ,TopLayer5SNAA031A May2006 RevisedMay2013AN-1490LM4702PowerAmplifie rSubmitDocumentationFeedbackCopyright 2006 2013, ,TopSilkscreen6AN-1490LM4702PowerAmplifi erSNAA031A May2006 RevisedMay2013SubmitDocumentationFeedbac kCopyright 2006 2013, , newTexasInstrumentswaferfabricationproce ssis + alsoprovidesinversethermaltrackingtomain tainthebiaslevelastheoutputstagetemperat urechanges, (presentlya D44C8ora TIP31A) arephysicallymountedontheheatsinkbetween theNPNandPNPDarlingtonoutputdevices, + moreClassA regionofoperationwastested,buttherewasno improvementin THD+ May2006 RevisedMay2013AN-1490LM4702PowerAmplifie rSubmitDocumentationFeedbackCopyright 2006 2013, degenerationresistorsin theemittercircuitsoftheDarlingtontransis torsusedin , theLM4702DemonstrationStereoPowerAmplifi eris a simpleunregulated, theenclosureandtheirabilitytoprovide100W perchannelintoan8 ,oneoneachsideoftheenclosure,togetthereq uiredVA(VoltsX Amp)ratingandstillfit in # s andsuppliers,seeTable1. Thisconfigurationofonetransformeroneachs ideoftheenclosureallowedtheuseofa separatetransformeranddiodebridgeforeach ofthe50VDC(positiveandnegative)supplyrai lsin ,thecloseproximityofthetwotoroidaltransf ormerstothecircuitboardnecessitatedshiel dingbothtransformerswith Mu-Metal , ,evenwiththelowerlevelmagneticfieldsthat theyradiate, onlyeffectivewhenit makesa completelooparoundtheentireperimeterofth etoroidaltransformerbutit F a F capacitoracrosstheplusandminus50VDCrails (fromthepositivetothenegativerail).Thisc apacitoris alsoa pairofthesamecapacitorsacrossthetwolarge 27,000 F mostoftenthecasein audiopoweramplifierdesign,theirvaluewasc hosenbasedonwhatwasthelargestvalue,lowes tESRcapacitoravailablewitha thebox! , , outputlevelsata singlelocationfora singlelistenerisrecommended, May2006 RevisedMay2013SubmitDocumentationFeedbac kCopyright 2006 2013, POWER (W)THD+N (%) + 'ssoundroomevaluatingdifferentcircuitcom ponentsusedin theLM4702demoamplifier, ,withdifferentparticipantsandatvariouslo cationsaroundthecountry,thenegativeeffec tsofeventhebestfilmandfoilpolystyreneDCb lockinginputcapacitorsin is thereforerecommendedthatDCblockingcapaci torsnotbeusedin problemthentheuseofa DCservocircuitthatkeepsDCoffsetfromappea ringattheoutputoftheamplifieris significantamounthasbeenwrittenin thedemoamplifierarestandard, ,stargroundandstarpowerroutingofsupplywi reswillimprovenoisemeasurementsandhavean effectonperceived soundquality .LargegaugewirewillreduceIRlosses(Curren tX Resistancelosses) basicrequirementin + +NvsOutputPowerRL= 8 , Vsupply= 50VDC9SNAA031A May2006 RevisedMay2013AN-1490LM4702PowerAmplifie rSubmitDocumentationFeedbackCopyright 2006 2013,TexasInstrumentsIncorporatedBillofM aterials(BOM) (BOM)AnalogAudioLM4702TACompact100WAMPDe moBoardAssemblyPartNumber:980012762 5WResistorRep1a-2a,RenNewark02F13441a-2a 34Res68K 1% 2,Rf1 1% +,Rin-,DigikeyRin2+,Rin2 1% , 1% , 1% 1% , 1% , 1 TurnTopAdjustResistorPot1,Pot2Digikey334 5P-201 F 250VDCRadialCapacitorCs1,Cs2, F 100VDCRadialCapacitorSeeDrawingPanasonic ECQ-E4105KF134CapMica30pF500VRadialCapac itorCc1,Cc2,Cb2,DigikeyCb4338 1076 ND142CapMica30pF500VRadialCapacitorCrs1, Crs2Digikey338 1076 ND152ElectrolyticCap220 F 35VRadialCapacitorCi1a, F F F 630VDCRadialCapacitorCsn1,Csn2PanasonicE CQ-E6223KZ192TransistorTIP31ATransistorS eeDrawingFairchildD44C8202TransistorMN24 88DarlingtonSeeDrawingNewark37C2041212Tr ansistorMP1620DarlingtonSeeDrawingNewark 37C2111222ConnectorVertPCB3 PosConnectorSeeDrawingMolex26 61 4030234BindingPostConnectorSeeDrawingDig ikey111 2223 001244ConnectorVertPCB5 PosOutputConnectorSeeDrawingMolex26 61 4060251ConnectorVertPCB6 PosPowerConnectortoSeeDrawingMolex26 61 4060LM4702chip262Wire16AWGJumperL1,L210A N-1490LM4702PowerAmplifierSNAA031A May2006 RevisedMay2013SubmitDocumentationFeedbac kCopyright 2006 2013, s ownsetofuniqueconstraintsthatwillbehavet obedealtwithbythedesignerbutthesimplicit yoftheLM4702keepstheseconstraintstoa minimumandit doesthisata levelofdistortion( a completeamplifier)andaudibleaudioquality thatis unmatched!11SNAA031A May2006 RevisedMay2013AN-1490LM4702PowerAmplifie rSubmitDocumentationFeedbackCopyright 2006 2013,TexasInstrumentsIncorporatedIMPORTA NTNOTICETexasInstrumentsIncorporatedandi tssubsidiaries(TI)reservetherighttomakec orrections,enhancements,improvementsando therchangestoitssemiconductorproductsand servicesperJESD46,latestissue,andtodisco ntinueanyproductorserviceperJESD48, (alsoreferredtohereinas components ) aresoldsubjecttoTI s ,in accordancewiththewarrantyin TI s ,testingofallparametersofeachcomponentis productsandapplications, ,eitherexpressorimplied,is grantedunderanypatentright,copyright,mas kworkright,orotherintellectualpropertyri ghtrelatingtoanycombination,machine,orpr ocessin licensetousesuchproductsorservicesora licensefroma thirdpartyunderthepatentsorotherintellec tualpropertyofthethirdparty,ora TIdatabooksordatasheetsis permissibleonlyif reproductionis withoutalterationandis accompaniedbyallassociatedwarranties,con ditions,limitations, is solelyresponsibleforcompliancewithallleg al,regulatoryandsafety-relatedrequiremen tsconcerningitsproducts,andanyuseofTIcom ponentsin itsapplications, hasallthenecessaryexpertisetocreateandim plementsafeguardswhichanticipatedangerou sconsequencesoffailures,monitorfailuresa ndtheirconsequences, , ,TI s goalis , FDAClassIII(orsimilarlife-criticalmedica lequipment)unlessauthorizedofficersofthe partieshaveexecuteda enhancedplastic solelyattheBuyer's risk,andthatBuyeris solelyresponsibleforcompliancewithallleg alandregulatoryrequirementsin , , , :TexasInstruments,PostOfficeBox655303,Da llas,Texas75265Copyright 2013,TexasInstrumentsIncorporated

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