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Abstract:ONSemiconductor(OnSemi)CompanyA-B-typemainNCP2890audiopoweramplifierperformancecharacteristicsandthebasicworkingprinciple,givethedesignoftheNCP2890audioamplifierwithatypicalapplicationcircuitanddesignmethod.Keywords:NCP2890；ABtype；audioamplifier1outlinesONSemiconductorNCP2890are(OnSemi)hasintroducedcost-effective,full-featuredaudioSeriesProductsofthefirstaudiopoweramplifier,itisdesignedformobilephoneandPDA,suchasbattery-poweredwirelessdevicesdesignedforproduction,areonekindsofverygoodqualitywirelessapplicationsA-B-typeaudiopoweramplifiercanprovidecustomerswithsuperioraudioperformance.Thedevicehasasuperiorpowersupplyrejectionratio(PSRR)andtotalharmonicdistortionplusnoise(THD+N)characteristicsatthesametime,acombinationofexternalcontrolgaincharacteristicsandadjustablebootandshutdowntimedelayfunction,andhaveastartupandshutdowncontrolcircuitthatcaneliminatetheopeningandclosingofsuchaudiopoweramplifiergeneratedaudiblenoise,canbeflexiblyusedinportableaudioequipmentdesign.NCP2890allowslithium-ionorlithiumpolymerbatterydirectpowersupply,andthusobviatestheextraLowDropoutRegulators(LDO),whilereducingboardspaceandreducestheoverallcost.2-chipstructureandperformanceparametersTomeetthespecificneedsofthemarket,NCP2890currentlyhaveMi-crobump-9(2.25mm2)andMicro-8(14.7mm2)twodifferentkindsofpackagingforms,showninFigure1withitspindiagram,allcitedthefunctionofthefootsuchasTable1NCP2890include671internaltransistor,MOSgate1899,whichhasexcellentaudioperformance,Table2givetheNCP2890themainperformanceparameters.Table2NC2890mainperformanceparameters3ApplicationCircuitDesignFigure2showsatypicalNCP2890audioamplifierapplicationcircuit,Figure2canbeseenfrom,NCP2890externalonlyusedtoadjustthegainofthetworesistors,aninputcouplingcapacitor,abypasscapacitor,suchasasmallnumberofcomponents,thereforetheexternalrequirementsdevicesextremelyeasy3.1WorkingPrinciplecircuitNCP2890containstwoidenticalpoweramplifiers,theinputaudiosignalbythefirstpoweramplifieramplifiedtheoutputfromtheOUTA.VoltagegainbyexternalresistorRfandRintheratioofthedecision.TheaudiosignalamplifiedbythegainofoneandthenthesecondpoweramplifierRPenlarge,andOUTBoutput.BecauseofOUTAandOUTBclient-sideaudiooutputsignalpowerequaltothesize,phasecontrast,andtwooutputs(OUTAandOUTB)DCthesamestaticpotential(Vp/2),so,speakerscanbeconnecteddirectlytotheclientOUTAandOUTB,ratherthanincreasetheoutputcouplingcircuit.TwopoweramplifieroutputstageusingPMOSandNMOStransistorsbythespecialdesign.Normalconduction,thechannelresistanceoflessthan0.6,andthusitsoutputwaveformdistortionisverysmall.Generalpoweramplifierintheopenandturnofftheprocesswillproducethehumanearcanhearthenoise,inordertoeliminateaudiblenoise,in-housedesignedNCP2890noiseeliminationcircuit.Boottime,addtheswitchcontrollogichighendofbypasscapacitorCbyontheDCvoltagevaluesbegintoincreaseexponentiallywhenthevoltagevaluereachesthevalueofcommon-modevoltage(Vp/2)whenthebeginningofoutputpower(thisprocessaround50ms)；andshutdown,thecontrollow-leveltermination,loadtobeconnectedtothegroundingterminal,theoutputpowertozero,whentheDCcircuitquiescentcurrentlessthan100nA3.2circuitelementparametersRinandRfamplifierusedtosettheclosed-loopgain,NCP2890inordertooptimizetheperformanceoftheclosed-loopgainamplifiershouldbesetatarelativelylowlevel,THDatthistimethesmallest,thelargestsignaltonoiseratio,widefrequencyresponserange.Soinmostcases,theclosed-loopgainamplifierinstalledingeneralbetween25,therefore,inputresistance(Rin)valuesofDinthe20kmoreappropriate,andRfisusedtoadjusttheclosed-loopgaintocontroltheoutputpower.InputcouplingcapacitorCininputamplifierusedtoisolatetheDCvoltage,Rinsimultaneouslywiththeformationofahigh-passfilter,butitwillaffectthefiltercutofffrequencythreshold.Inordertoenablethelow-frequencysignalsdonotdecaytoogreat,intheory,Cinshouldtakealargervalue,whilethelargercapacitorchargeanddischargetimeislong,therefore,requiredalongerperiodoftimetomakeinputtoreachthestaticpotentialVp/2,whichiseasytomaketheoutputnoisegeneratedboot.Therefore,inmostcases,Cinvaluesgenerallybetween0.10.39Fmoreappropriate(Rin=20kpm).BypasscapacitorCbyarecommon-modevoltage(Vp/2)ofthefilter,istodeterminethelengthoftheboot,bootnoisereductionasakeycomponent,inmostcases,1.0FbypasscapacitorCbycheckmoreappropriate.R1andR2componentsofthepartialpressurecircuitchipsusedtoproducethestartvoltage,generalR1value100k,designedaccordingtovoltagevaluetoselecttheresistanceR2,aslongasthepressuresothatthevalueisgreaterthan1.2Vcanbeabout3.3CautionWhenthecircuitreachesthemaximumoutputpowerPorms=1.0W,Vp=5.0V,RL=8.0whentheloadonthepeakcurrentof500mA.Inordertopreventtheoutputloadcircuitwhentheoutputcurrentistoolarge,setupchipoutputcurrentdetectioncircuit,itcanbelimitedtoamaximumoutputcircuit800mA.Inthisway,oncetheoutputcurrentofover800mA,theoutputsideofthefourMOStransistorswillbegatedoffandnolongervoltageoutputcurrent.Whenthechiptemperatureexceeds160,theinternalamplifierwillbeshutdownandstopworkinguntilthetemperatureisbelow140,theinternalamplifiertobeginworktorestart.DespitetheNCP2890containsaninternalover-currentandover-temperatureprotectioncircuit,butwheninuse,wemustpayattentiontopowersupplyvoltageshouldnotexceedtheirlimits,soastoavoidchipdamage.摘要：介紹了安森美半導(dǎo)體(OnSemi)公司類音頻功率放大器NCP2890的主要性能特點(diǎn)和基本工作原理，給出了用NCP2890設(shè)計(jì)音頻功放的典型應(yīng)用電路和設(shè)計(jì)方法。關(guān)鍵詞：NCP2890；A-B類；音頻放大器1概述是安森美半導(dǎo)體()公司推出的經(jīng)濟(jì)高效、功能齊備的音頻系列產(chǎn)品中的第一款音頻功率放大器，它是專為手機(jī)和等電池供電的無(wú)線設(shè)備而設(shè)計(jì)生產(chǎn)的，是一種質(zhì)量非常優(yōu)秀的無(wú)線應(yīng)用類音頻功率放大器，可為客戶提供卓越的音頻性能。該器件在具有出眾的電源抑制比()和總諧波失真加噪聲()特性的同時(shí)，綜合了外部控制增益特征和可調(diào)式開(kāi)機(jī)與關(guān)機(jī)延時(shí)功能，并具有“開(kāi)機(jī)和關(guān)機(jī)”控制電路，能消除開(kāi)啟和關(guān)閉此類音頻功率放大器時(shí)產(chǎn)生的可聽(tīng)噪聲，可靈活應(yīng)用于便攜式音頻設(shè)備的設(shè)計(jì)中。允許鋰離子或鋰聚合物電池直接供電，因而省卻了額外的低壓降穩(wěn)壓器()，同時(shí)減少了電路板的占用空間并降低了整體成本.2芯片結(jié)構(gòu)與性能參數(shù)為滿足特定市場(chǎng)的需求，目前有-()和()兩種不同的封裝形式，圖所示為其引腳排列圖，各引腳的功能如表列.內(nèi)部包括個(gè)晶體管、個(gè)門電路，因而具有極佳的音頻性能，表給出了的主要性能參數(shù).應(yīng)用電路設(shè)計(jì)圖所示為音頻功放的典型應(yīng)用電路，由圖可見(jiàn)，外圍只有用來(lái)調(diào)節(jié)增益的兩個(gè)電阻、一個(gè)輸入耦合電容、一個(gè)旁路電容等少數(shù)幾個(gè)元件，因此所需外圍器件極其簡(jiǎn)單電路工作原理內(nèi)含兩個(gè)完全一樣的功率放大器，輸入的音頻信號(hào)經(jīng)第一個(gè)功率放大器放大后從輸出。電壓增益由外接電阻與的比值決定。放大后的音頻信號(hào)再經(jīng)增益為的第二個(gè)功率放大器進(jìn)行反相放大，并從輸出。由于端與端輸出的音頻功率信號(hào)大小相等、相位相反，且兩個(gè)輸出端(和)的直流靜態(tài)電位相同（），所以，揚(yáng)聲器可以直接連接到與端，而不用增加輸出耦合電路。兩個(gè)功率放大器的輸出級(jí)均采用和晶體管特殊設(shè)計(jì)而成。正常導(dǎo)通時(shí)，其溝道電阻小于，因而其輸出波形失真非常小.一般的功率放大器在開(kāi)啟和關(guān)閉過(guò)程中會(huì)產(chǎn)生人耳可聽(tīng)到的噪聲，為了消除這種可聽(tīng)噪聲，在內(nèi)部專門設(shè)計(jì)了消噪聲電路。開(kāi)機(jī)時(shí)，邏輯高電平加到開(kāi)關(guān)控制端，旁路電容上的直流電壓值開(kāi)始按指數(shù)規(guī)律增加，當(dāng)電壓值達(dá)到共模電壓值（）時(shí)，開(kāi)