LM675PowerOperationalAmplifierMay1999
LM675
PowerOperationalAmplifier
GeneralDescription
TheLM675isamonolithicpoweroperationalamplifierfea-turingwidebandwidthandlowinputoffsetvoltage,makingitequallysuitableforACandDCapplications.
TheLM675iscapableofdeliveringoutputcurrentsinexcessof3amps,operatingatsupplyvoltagesofupto60V.Thede-viceoverloadprotectionconsistsofbothinternalcurrentlim-itingandthermalshutdown.Theamplifierisalsointernallycompensatedforgainsof10orgreater.
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1mVtypicaloffsetvoltageShortcircuitprotection
Thermalprotectionwithparolecircuit(100%tested)16V–60VsupplyrangeWidecommonmoderange
Internaloutputprotectiondiodes90dBripplerejection
PlasticpowerpackageTO-220
Features
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3AcurrentcapabilityAVOtypically90dB
5.5MHzgainbandwidthproduct8V/µsslewrate
Widepowerbandwidth70kHz
Applications
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HighperformancepoweropampBridgeamplifiersMotorspeedcontrolsServoamplifiersInstrumentsystems
ConnectionDiagram
TO-220PowerPackage(T)
TypicalApplications
Non-InvertingAmplifier
DS006739-1
*Thetabisinternallyconnectedtopin3(−VEE)
FrontView
OrderNumberLM675TSeeNSPackageT05D
DS006739-2
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AbsoluteMaximumRatings(Note1)
IfMilitary/Aerospacespecifieddevicesarerequired,pleasecontacttheNationalSemiconductorSalesOffice/Distributorsforavailabilityandspecifications.SupplyVoltageInputVoltage
OperatingTemperature
±30V
−VEEtoVCC0˚Cto+70˚C
StorageTemperatureJunctionTemperature
PowerDissipation(Note2)LeadTemperature
(Soldering,10seconds)ESDratingtobedetermined.
−65˚Cto+150˚C
150˚C30W
260˚C
ElectricalCharacteristics
VS=±25V,TA=25˚Cunlessotherwisespecified.
Parameter
SupplyCurrentInputOffsetVoltageInputBiasCurrentInputOffsetCurrentOpenLoopGainPSRRCMRR
OutputVoltageSwing
OffsetVoltageDriftVersusTemperatureOffsetVoltageDriftVersusOutputPowerOutputPower
GainBandwidthProductMaxSlewRate
InputCommonModeRange
THD=1%,fO=1kHz,RL=8ΩfO=20kHz,AVCL=1000POUT=0WVCM=0VVCM=0VVCM=0VRL=∞Ω∆VS=±5VVIN=±20VRL=8ΩRS<100kΩ
Conditions
Typical1810.250909090
TestedLimit50(max)10(max)2(max)500(max)70(min)70(min)70(min)
UnitsmAmVµAnAdBdBdBVµV/˚CµV/W
20
WMHzV/µs
±21
2525255.58
±18(min)
±22±20(min)V
Note1:AbsoluteMaximumRatingsindicatelimitsbeyondwhichdamagetothedevicemayoccur.OperatingRatingsindicateconditionsforwhichthedeviceisfunc-tional,butdonotguaranteespecificperformancelimits.ElectricalCharacteristicsstateDCandACelectricalspecificationsunderparticulartestconditionswhichguar-anteespecificperformancelimits.ThisassumesthatthedeviceiswithintheOperatingRatings.Specificationsarenotguaranteedforparameterswherenolimitisgiven,however,thetypicalvalueisagoodindicationofdeviceperformance.
Note2:AssumesTAequalto70˚C.Foroperationathighertabtemperatures,theLM675mustbederatedbasedonamaximumjunctiontemperatureof150˚C.
TypicalApplications
GeneratingaSplitSupplyFromaSingleSupply
DS006739-3
VS=±8V→±30V
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TypicalPerformanceCharacteristics
THDvsPowerOutput
InputCommonModeRangevsSupplyVoltage
SupplyCurrentvsSupplyVoltage
DS006739-10
DS006739-11
DS006739-12
PSRRvsFrequency
DeviceDissipationvsAmbientTemperature†CurrentLimitvsOutputVoltage*
DS006739-13
DS006739-14
DS006739-15
†θINTERFACE=1˚C/W
SeeApplicationHints.
*VS=±25V
IBvsSupplyVoltage
OutputVoltage
SwingvsSupplyVoltage
DS006739-16
DS006739-17
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SchematicDiagram
DS006739-5www.national.com4
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ApplicationHints
STABILITY
TheLM675isdesignedtobestablewhenoperatedataclosed-loopgainof10orgreater,but,aswithanyotherhigh-currentamplifier,theLM675canbemadetooscillateundercertainconditions.Theseusuallyinvolveprintedcir-cuitboardlayoutoroutput/inputcoupling.
Whendesigningaprintedcircuitboardlayout,itisimportanttoreturntheloadground,theoutputcompensationground,andthelowlevel(feedbackandinput)groundstothecircuitboardgroundpointthroughseparatepaths.Otherwise,largecurrentsflowingalongagroundconductorwillgeneratevolt-agesontheconductorwhichcaneffectivelyactassignalsattheinput,resultinginhighfrequencyoscillationorexcessivedistortion.Itisadvisabletokeeptheoutputcompensationcomponentsandthe0.1µFsupplydecouplingcapacitorsascloseaspossibletotheLM675toreducetheeffectsofPCBtraceresistanceandinductance.Forthesamereason,thegroundreturnpathsforthesecomponentsshouldbeasshortaspossible.
Occasionally,currentintheoutputleads(whichfunctionasantennas)canbecoupledthroughtheairtotheamplifierin-put,resultinginhigh-frequencyoscillation.Thisnormallyhappenswhenthesourceimpedanceishighortheinputleadsarelong.Theproblemcanbeeliminatedbyplacingasmallcapacitor(ontheorderof50pFto500pF)acrossthecircuitinput.
Mostpoweramplifiersdonotdrivehighlycapacitiveloadswell,andtheLM675isnoexception.IftheoutputoftheLM675isconnecteddirectlytoacapacitorwithnoseriesre-sistance,thesquarewaveresponsewillexhibitringingifthecapacitanceisgreaterthanabout0.1µF.Theamplifiercantypicallydriveloadcapacitancesupto2µForsowithoutos-cillating,butthisisnotrecommended.Ifhighlycapacitiveloadsareexpected,aresistor(atleast1Ω)shouldbeplacedinserieswiththeoutputoftheLM675.Amethodcommonlyemployedtoprotectamplifiersfromlowimpedancesathighfrequenciesistocoupletotheloadthrougha10Ωresistorinparallelwitha5µHinductor.
CURRENTLIMITANDSAFEOPERATINGAREA(SOA)PROTECTION
Apoweramplifier’soutputtransistorscanbedamagedbyexcessiveappliedvoltage,currentflow,orpowerdissipation.Thevoltageappliedtotheamplifierislimitedbythedesignoftheexternalpowersupply,whilethemaximumcurrentpassedbytheoutputdevicesisusuallylimitedbyinternalcircuitrytosomefixedvalue.Short-termpowerdissipationisusuallynotlimitedinmonolithicoperationalpoweramplifiers,andthiscanbeaproblemwhendrivingreactiveloads,whichmaydrawlargecurrentswhilehighvoltagesappearontheoutputtransistors.TheLM675notonlylimitscurrenttoaround4A,butalsoreducesthevalueofthelimitcurrentwhenanoutputtransistorhasahighvoltageacrossit.
Whendrivingnonlinearreactiveloadssuchasmotorsorloudspeakerswithbuilt-inprotectionrelays,thereisapossi-bilitythatanamplifieroutputwillbeconnectedtoaloadwhoseterminalvoltagemayattempttoswingbeyondthepowersupplyvoltagesappliedtotheamplifier.Thiscancausedegradationoftheoutputtransistorsorcatastrophicfailureofthewholecircuit.Thestandardprotectionforthistypeoffailuremechanismisapairofdiodesconnectedbe-
tweentheoutputoftheamplifierandthesupplyrails.ThesearepartoftheinternalcircuitryoftheLM675,andneedn’tbeaddedexternallywhenstandardreactiveloadsaredriven.THERMALPROTECTION
TheLM675hasasophisticatedthermalprotectionschemetopreventlong-termthermalstresstothedevice.Whenthetemperatureonthediereaches170˚C,theLM675shutsdown.Itstartsoperatingagainwhenthedietemperaturedropstoabout145˚C,butifthetemperatureagainbeginstorise,shutdownwilloccuratonly150˚C.Therefore,thede-viceisallowedtoheatuptoarelativelyhightemperatureifthefaultconditionistemporary,butasustainedfaultwilllimitthemaximumdietemperaturetoalowervalue.ThisgreatlyreducesthestressesimposedontheICbythermalcycling,whichinturnimprovesitsreliabilityundersustainedfaultconditions.Thiscircuitryis100%testedwithoutaheatsink.Sincethedietemperatureisdirectlydependentupontheheatsink,theheatsinkshouldbechosenforthermalresis-tancelowenoughthatthermalshutdownwillnotbereachedduringnormaloperaton.Usingthebestheatsinkpossiblewithinthecostandspaceconstraintsofthesystemwillim-provethelong-termreliabilityofanypowersemiconductor.POWERDISSIPATIONANDHEATSINKING
TheLM675shouldalwaysbeoperatedwithaheatsink,eventhoughatidleworstcasepowerdissipationwillbeonly1.8W(30mAx60V)whichcorrespondstoariseindietem-peratureof97˚CaboveambientassumingθjA=54˚C/WforaTO-220package.Thisinitselfwillnotcausethethermalprotectioncircuitrytoshutdowntheamplifierwhenoperatingatroomtemperature,butamere0.9WofadditionalpowerdissipationwillshuttheamplifierdownsinceTJwillthenin-creasefrom122˚C(97˚C+25˚C)to170˚C.
Inordertodeterminetheappropriateheatsinkforagivenapplication,thepowerdissipationoftheLM675inthatappli-cationmustbeknown.Whentheloadisresistive,themaxi-mumaveragepowerthattheICwillberequiredtodissipateisapproximately:
whereVSisthetotalpowersupplyvoltageacrosstheLM675,RListheloadresistanceandPQisthequiescentpowerdissipationoftheamplifier.Theaboveequationisonlyanapproximationwhichassumesan“ideal”classBout-putstageandconstantpowerdissipationinallotherpartsofthecircuit.Asanexample,iftheLM675isoperatedona50Vpowersupplywitharesistiveloadof8Ω,itcandevelopupto19Wofinternalpowerdissipation.Ifthedietemperatureistoremainbelow150˚Cforambienttemperaturesupto70˚C,thetotaljunction-to-ambientthermalresistancemustbelessthan
UsingθJC=2˚C/W,thesumofthecase-to-heatsinkinter-facethermalresistanceandtheheat-sink-to-ambientther-malresistancemustbelessthan2.2˚C/W.Thecase-to-heat-sinkthermalresistanceoftheTO-220packagevarieswiththemountingmethodused.Ametal-to-metalin-terfacewillbeabout1˚C/Wiflubricated,andabout1.2˚C/Wifdry.Ifamicainsulatorisused,thethermalresistancewillbeabout1.6˚C/Wlubricatedand3.4˚C/Wdry.Forthisex-
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ApplicationHints
(Continued)
ample,weassumealubricatedmicainsulatorbetweentheLM675andtheheatsink.Theheatsinkthermalresistancemustthenbelessthan
4.2˚C/W−2˚C/W−1.6˚C/W=0.6˚C/W.Thisisaratherlargeheatsinkandmaynotbepracticalinsomeapplications.Ifasmallerheatsinkisrequiredforrea-sonsofsizeorcost,therearetwoalternatives.Themaxi-mumambientoperatingtemperaturecanberestrictedto50˚C(122˚F),resultingina1.6˚C/Wheatsink,ortheheatsinkcanbeisolatedfromthechassissothemicawasherisnotneeded.Thiswillchangetherequiredheatsinktoa1.2˚C/Wunitifthecase-to-heat-sinkinterfaceislubricated.
Thethermalrequirementscanbecomemoredifficultwhenanamplifierisdrivingareactiveload.Foragivenmagnitudeofloadimpedance,ahigherdegreeofreactancewillcauseahigherlevelofpowerdissipationwithintheamplifier.Asageneralrule,thepowerdissipationofanamplifierdrivinga60˚reactiveloadwillberoughlythatofthesameamplifierdrivingtheresistivepartofthatload.Forexample,somere-activeloadsmayatsomefrequencyhaveanimpedancewithamagnitudeof8Ωandaphaseangleof60˚.Therealpartofthisloadwillthenbe8Ωxcos60˚or4Ω,andtheam-plifierpowerdissipationwillroughlyfollowthecurveofpowerdissipationwitha4Ωload.
TypicalApplications
Non-InvertingUnityGainOperation
DS006739-6
InvertingUnityGainOperation
DS006739-7
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TypicalApplications
(Continued)
ServoMotorControl
DS006739-8
HighCurrentSource/Sink
DS006739-9
IOUT=VINx2.5amps/volt
i.e.IOUT=1AwhenVIN=400mVTrimpotformaxROUT
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LM675PowerOperationalAmplifierPhysicalDimensions
inches(millimeters)unlessotherwisenoted
TO-220PowerPackage(T)OrderNumberLM675TNSPackageT05D
LIFESUPPORTPOLICY
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