www.ti.com SNAS094D – APRIL 1995– REVISED MARCH 2013 ...

1 APRIL1995 REVISEDMARCH2013LM1972 Pot2-Channel78dBAudioAttenuatorwithMuteC heckforSamples:LM19721 FEATURESDESCRIPTIONTheLM1972isa digitallycontrolled2-channel78dB2 3-WireSerialInterfaceaudioattenuatorfabr icatedonaCMOS process. 104dBMuteAttenuation0dB , 78dB, PopandClickFreeAttenuationChangesattenua tioncurvecanbecustomizedthroughsoftwaret ofit Potisdemonstratedthrough AutomatedStudioMixingConsolesitsexcellen tSignal-to-NoiseRatio,extremelylow MusicReproductionSystems(THD+N), Pot SoundReinforcementSystemscontainsa mutefunctionthatdisconnectstheinputsigna lfromtheoutput,providingaminimum ElectronicMusic(MIDI) 's3-wireserialdigitalinterfaceisTTLKEYSP ECIFICATIONSandCMOS compatible;receivingdatathatselectsa TotalHarmonicDistortion+ (max)OutpinoftheLM1972allowsmultiple Potstobedaisy-chainedtogether,reducingth enumberof Frequencyresponse:100kHz( 3dB)(min)enableanddatalinestoberoutedfor agiven Attenuationrange( ):78dB(typ) Differentialattenuation: (max) Signal-to-noiseratio( Vrms):110dB(min) Channelseparation:100dB(min) TopViewCircuitSeeDWPackage1 Pleasebeawarethatanimportantnoticeconcer ningavailability,standardwarranty,anduse in 1995 2013, APRIL1995 (1)(2)(3)SupplyVoltage(VDD VSS)15 VVoltageatAnyPinVSS + (4)150mWESDS usceptabiIity(5)2000 VJunctionTemperature150 CSolderingInformationDWPackage(10sec.)

2 +260 CStorageTemperature 65 C to+150 C(1)AllvoltagesaremeasuredwithrespecttoG NDpins(1,3,5,6,14,16,19),unlessotherwise specified.(2) a goodindicationofdeviceperformance.(3)If Military/Aerospacespecifieddevicesarereq uired,pleasecontacttheTexasInstrumentsSa lesOffice/Distributorsforavailabilityand specifications.(4)Themaximumpowerdissipa tionmustbederatedatelevatedtemperaturesa ndis dictatedbyTJMAX, JA, andtheambienttemperatureTA. Themaximumallowablepowerdissipationis PD= (TJMAX TA)/ JAorthenumbergivenin theAbsoluteMaximumRatings,whicheveris ,TJMAX= +150 C,andthetypicaljunction-to-ambienttherma lresistance,whenboardmounted,is65 C/W.(5)Humanbodymodel,100pFdischargedthr ougha (1)(2)TMINTATMAXT emperatureRangeTMIN TA TMAX0 C TA +70 CSupplyVoltage(VDD VSS) (1)AllvoltagesaremeasuredwithrespecttoGN Dpins(1,3,5,6,14,16,19),unlessotherwises pecified.

3 (2) a 1995 2013, APRIL1995 REVISEDMARCH2013 ElectricalCharacteristics(1)(2)Thefollow ingspecificationsapplyforallchannelswith VDD= +6V,VSS= 6V,VIN= ,andf = 1 kHz, 25 (Limits)Typical(3)Limit(4)ISSupplyCurren tInputsareACGrounded24mA(max)THD+NTotalH armonicDistortionplusNoiseVIN= @ 78dBSNRS ignal-to-NoiseRatioInputsareACGrounded@ 12dBAttenuation120110dB(min)A-WeightedAM MuteAttenuation10496dB(min)AttenuationSt epSizeError0dBto (max) 48dBto 78dB @ (min)Attenuation@ (min)Attenuation@ (min)Attenuation@ (min)Channel-to-ChannelAttenuationAttenu ation@0dB, 20dB, 40dB, 60dB (max)TrackingErrorAttenuation@ 78dB (max) (max)RINACI nputImpedancePins4,20,VIN= ,f = 1 kHz4020k (min)60k (max)IINI nputCurrent@Pins9,10,11@0V< VIN< (max)Data-OutLevels(Pin12)VDD=6V,VSS= (max) (min)(1)Allvoltagesaremeasuredwithrespec ttoGNDpins(1,3,5,6,14,16,19),unlessother wisespecified.

4 (2) a goodindicationofdeviceperformance.(3)Typ icalsaremeasuredat25 C andrepresenttheparametricnorm.(4)Limitsa respecifiedtoTexasInstrument's AOQL(AverageOutputQualityLevel).Copyrigh t 1995 2013,TexasInstrumentsIncorporatedSubmitD ocumentationFeedback3 ProductFolderLinks:LM1972LM1972 SNAS094D APRIL1995 (3,19):Eachinputhasitsownindependentgrou nd, (4,20):Thereare2 independentsignalinputs, (2,17):Thereare2 independentsignaloutputs, (13,15):Positivevoltagesupplypins, (7,18):Negativevoltagesupplypins,VSS1and VSS2. Tobetiedtogroundin a (1,5,6,14,16):Thesefivepinsarenotphysica llyconnectedtothediein anyway( ,Nobondwires). , (8):Digitalsignalgroundfortheinterfaceli nes;CLOCK,LOAD/SHIFT, (9):Theclockinputacceptsa (10):Theload/shiftinputacceptsa theenablepinofthedevice,allowingdatatobe clockedin whilethisinputis low(0V).

5 Data-In(11):Thedata-ininputacceptsa usedtoacceptserialdatafroma microcontrollerthatwillbelatchedanddecod edtochangea channel' (12):Thispinis usedin daisy-chainmodewheremorethanone Potis clockedintothechainfromthe C,theprecedingdatain theshiftregisteris shiftedouttheDATA-OUTpintothenext Potin thechainortogroundif it is thelast Potin 1995 2013, APRIL1995 REVISEDMARCH2013 ConnectionDiagramCopyright 1995 2013,TexasInstrumentsIncorporatedSubmitD ocumentationFeedback5 ProductFolderLinks:LM1972LM1972 SNAS094D APRIL1995 VSS= KHzbyFFTVDD VSS= 1995 2013, APRIL1995 REVISEDMARCH2013 TypicalPerformanceCharacteristics(contin ued)THD+ N vsFrequencyandAmplitudeFFTof1 + + NTHD+ 1995 2013,TexasInstrumentsIncorporatedSubmitD ocumentationFeedback7 ProductFolderLinks:LM1972LM1972 SNAS094D APRIL1995 PotisshowninFigure16.

6 Thisattenuationstepscheme,however, constantlogarithmicattenuationschemeof1d Bstepsfora panningfunctionasshowninFigure17. Theonlyrestrictiontothecustomizationofat tenuationschemesarethegivenattenuationle velsandtheircorrespondingdatabitsshownin Table1. ,theattenuationlevelwillbechangedcorresp ondingtothedatabitsshowninTable1. AsshowninFigure19, anLM1972canbeconfiguredasa ( ) 1995 2013, APRIL1995 REVISEDMARCH2013LM1972 ChannelAttenuationvsDigitalStepValue( ) Potis constantata nominal40k . ToeliminateanyunwantedDCcomponentsfrompr opagatingthroughthedeviceit is commontouse1 F notnecessary,however, , Potvariestypicallybetween25k and35k Potismadeupofa resistorladdernetworkwitha logarithmicattenuation, ,a Potcannotbeconsideredasalinearpotentiome ter,butcanbeconsideredonlyasa shouldbenotedthatthelinearityofa Potcannotbemeasureddirectlywithouta bufferbecausetheinputimpedanceofmostmeas urementsystemsis ,theoutputofthe ,a Potis Potis itsabilitytomutetheinputsignaltoanattenu ationlevelof104dBasshowninFigure16.

7 Thisis accomplishedinternallybyphysicallyisolat ingtheoutputfromtheinputwhilealsogroundi ngtheoutputpinthroughapproximately2 k .Copyright 1995 2013,TexasInstrumentsIncorporatedSubmitD ocumentationFeedback9 ProductFolderLinks:LM1972LM1972 SNAS094D APRIL1995 (to11111111) mutebuttonontohissystemwhichcouldcausea microcontrollertosendtheappropriatedatat oa ,thedesignerhasa Potwasdesignedtobeusedasanattenuatorfors ignalswithintheaudiospectrum, bufferattheoutputofthe Pot, shouldalsoberememberedthattheoutputbuffe r'ssupplyvoltagedoesnothavetobethesameas the Pot' 3-wireserialcommunicationformatthatis easilycontrolledbya ,comprisedofDATA-IN,CLOCK,andLOAD/SHIFTi s showninFigure3. Figure3, theLOAD/SHIFT lineis bitsforchannelselectionand8 ,theMSBis sentfirstandthe8 bitsofaddressdataaretobesentbeforethe8 :LSBA ddressRegister(Byte0)00000000 Channel100000001 Channel200000010 Channel3 DataRegister(Byte1) : : : : :: : : : : :: : : : : :: :10 SubmitDocumentationFeedbackCopyright 1995 2013, APRIL1995 (continued) ( mute ) ( mute ): : : : :: ( mute ) ( mute ) PotSYSTEMARCHITECTUREThe Pot'sdigitalinterfaceisessentiallya shiftregister,whereserialdataisshiftedin ,latched, shiftedintotheDATA-INpin,thepreviouslyla tcheddatais ,theLOAD/SHIFT linegoeshigh, continuedeachandeverytimeanattenuationch angeis updated,only,whenthatchannelis selectedforanattenuatorchangeorthesystem is Potis poweredup,eachchannelis placedintothemutedmode.

8 PotLADDERARCHITECTUREE achchannelofa , theladderconsistsofmultipleR1 Table1. It canbeseeninFigure21thattheinputimpedance forthechannelis a constantvalueregardlessofwhichtapswitchi s selected, PotLadderArchitectureDIGITALLINECOMPATIB ILITYThe Pot'sdigitalinterfacesectionis compatiblewitheitherTTLorCMOS logicduetotheshiftregisterinputsactingup ona thresholdvoltageof2 1995 2013,TexasInstrumentsIncorporatedSubmitD ocumentationFeedback11 ProductFolderLinks:LM1972LM1972 SNAS094D APRIL1995 availablefordaisy-chainsystemconfigurati onswheremultiple , ,theDATA-OUTpinshouldbeterminatedthrough a 2 k resistorif ,however, PotSystemArchitectureDAISY-CHAINCAPABILI TYS incethe Pot'sdigitalinterfaceisessentiallya shiftregister,multiple Figure24, forann- Potdaisy-chain, Potsasit isforone ,thenthedataisclockedinsequentiallywhile theprecedingdataineach PotisshiftedouttheDATA-OUTpintothenext Potinthechainortogroundif it is thelast.

9 Latchingthedataintoeachoftheircorrespond ing (channelselection)andtheappropriatetapsw itchcontrollingtheattenuationlevelis Potasshownin theTypicalPerformanceCharacteristicswaso btainedbyplacinga is importanttobesurethatthesignallevelbeing measuredisofthesamefrequencysuchthata ,toensureanaccuratemeasurement,themeasur edchannel'sinputshouldbeACgroundedthroug ha 1 F 1995 2013, APRIL1995 REVISEDMARCH2013 CLICKSANDPOPSSo,whyisthatoutputbuffernee dedanyway?Therearethreeanswerstothisques tion,allofwhichareimportantfroma buffer/amplifierattheoutputofa Potis toensurethattherearenoaudibleclicksorpop sduetoattenuationstepchangesin anon-boardbipolaropamphadbeenusedfortheo utputstage,itsrequirementofa finiteamountofDCbiascurrentforoperationw ouldcausea DCvoltage pop whentheoutputimpedanceofthe ,thisphenomenonis duetothefactthattheoutputimpedanceofthe Potis changingwithstepchangesanda bipolaramplifierrequiresa ,sodoestheDCbiascurrentandthusthereis a DCvoltage pop.

10 Secondly,the Pothasnodrivecapability,soanydesiredgain needstobeaccomplishedthrougha ,theoutputofa Potneedstoseea JFET inputbufferprovidesa highinputimpedancetotheoutputofthe lownoisefloorandlowTHD+ Potis capableofbeingusedin thefeedbackloopofanamplifier,however,ass tatedpreviously,theoutputofthe Potneedstoseea highimpedancein , , a Potusedinthefeedbackloopcreatesa , ,however,becauseofthe Pot'sversatilitythegaincanbecontrolledth roughprogrammingsuchthattheclippinglevel ofthesystemis thatwheninmutemodetheinputis ,thusresultingin ,a PotDaisy-ChainedCircuitCopyright 1995 2013,TexasInstrumentsIncorporatedSubmitD ocumentationFeedback13 ProductFolderLinks:LM1972LM1972 SNAS094D APRIL1995 (March2013)toRevisionDPage 1995 2013,TexasInstrumentsIncorporatedProduct FolderLinks:LM1972 PACKAGE OPTION 1 PACKAGING INFORMATIONO rderable DeviceStatus(1)Package TypePackageDrawingPinsPackageQtyEco Plan(2)Lead/Ball Finish(6)MSL Peak Temp(3)Op Temp ( C)Device Marking(4/5)SamplesLM1972 MLIFEBUYSOICDW2036 TBDCall TICall TI0 to 70LM1972 MLM1972M/NOPBACTIVESOICDW2036 Green (RoHS& no Sb/Br)CU SNLevel-3-260C-168 HR0 to 70LM1972 MLM1972MX/NOPBACTIVESOICDW201000 Green (RoHS& no Sb/Br)CU SNLevel-3-260C-168 HR0 to 70LM1972M (1) The marketing status values are defined as follows:ACTIVE: Product device recommended for new : TI has announced that the device will be discontinued, and a lifetime-buy period is in : Not recommended for new designs.