LM231资料

LM231A/LM231/LM331A/LM331PrecisionVoltage-to-FrequencyConvertersJune1999

LM231A/LM231/LM331A/LM331

PrecisionVoltage-to-FrequencyConverters

GeneralDescription

TheLM231/LM331familyofvoltage-to-frequencyconvertersareideallysuitedforuseinsimplelow-costcircuitsforanalog-to-digitalconversion,precisionfrequency-to-voltageconversion,long-termintegration,linearfrequencymodula-tionordemodulation,andmanyotherfunctions.Theoutputwhenusedasavoltage-to-frequencyconverterisapulsetrainatafrequencypreciselyproportionaltotheappliedin-putvoltage.Thus,itprovidesalltheinherentadvantagesofthevoltage-to-frequencyconversiontechniques,andiseasytoapplyinallstandardvoltage-to-frequencyconverterappli-cations.Further,theLM231A/LM331Aattainanewhighlevelofaccuracyversustemperaturewhichcouldonlybeat-tainedwithexpensivevoltage-to-frequencymodules.Addi-tionallytheLM231/331areideallysuitedforuseindigitalsystemsatlowpowersupplyvoltagesandcanprovidelow-costanalog-to-digitalconversioninmicroprocessor-controlledsystems.And,thefrequencyfromabatterypoweredvoltage-to-frequencyconvertercanbeeasilychanneledthroughasimplephotoisolatortoprovideisolationagainsthighcommonmodelevels.

TheLM231/LM331utilizeanewtemperature-compensatedband-gapreferencecircuit,toprovideexcellentaccuracy

overthefulloperatingtemperaturerange,atpowersuppliesaslowas4.0V.Theprecisiontimercircuithaslowbiascur-rentswithoutdegradingthequickresponsenecessaryfor100kHzvoltage-to-frequencyconversion.Andtheoutputarecapableofdriving3TTLloads,orahighvoltageoutputupto40V,yetisshort-circuit-proofagainstVCC.

Features

nGuaranteedlinearity0.01%max

nImprovedperformanceinexistingvoltage-to-frequencyconversionapplications

nSplitorsinglesupplyoperationnOperatesonsingle5Vsupply

nPulseoutputcompatiblewithalllogicforms

nExcellenttemperaturestability,±50ppm/˚CmaxnLowpowerdissipation,15mWtypicalat5V

nWidedynamicrange,100dBminat10kHzfullscalefrequency

nWiderangeoffullscalefrequency,1Hzto100kHznLowcost

TypicalApplications

DS005680-1

*Usestablecomponentswithlowtemperaturecoefficients.SeeTypicalApplicationssection.**0.1µFor1µF,See“PrinciplesofOperation.”

FIGURE1.SimpleStand-AloneVoltage-to-FrequencyConverter

with±0.03%TypicalLinearity(f=10Hzto11kHz)

Teflon®isaregisteredtrademarkofDuPont

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AbsoluteMaximumRatings(Note1)

IfMilitary/Aerospacespecifieddevicesarerequired,pleasecontacttheNationalSemiconductorSalesOffice/Distributorsforavailabilityandspecifications.SupplyVoltage

OutputShortCircuittoGroundOutputShortCircuittoVCCInputVoltage

OperatingAmbientTemperatureRangePowerDissipation(PDat25˚C)andThermalResistance(θjA)

(NPackage)PDθjALeadTemperature(Soldering,10sec.)Dual-In-LinePackage(Plastic)ESDSusceptibility(Note4)NPackage

LM231A/LM23140V

ContinuousContinuous−0.2Vto+VSTMINTMAX−25˚Cto+85˚C

LM331A/LM33140V

ContinuousContinuous−0.2Vto+VSTMINTMAX0˚Cto+70˚C

1.25W100˚C/W260˚C500V

1.25W100˚C/W260˚C500V

ElectricalCharacteristics

TA=25˚Cunlessotherwisespecified(Note2)

Parameter

VFCNon-Linearity(Note3)

Conditions

4.5V≤VS≤20VTMIN≤TA≤TMAXVFCNon-Linearity

InCircuitofFigure1ConversionAccuracyScaleFactor(Gain)

LM231,LM231ALM331,LM331ATemperatureStabilityofGain

LM231/LM331LM231A/LM331AChangeofGainwithVSRatedFull-ScaleFrequencyGainStabilityvsTime(1000Hrs)

Overrange(BeyondFull-Scale)FrequencyINPUTCOMPARATOROffsetVoltage

LM231/LM331LM231A/LM331ABiasCurrentOffsetCurrentCommon-ModeRangeTIMER

TimerThresholdVoltage,Pin5InputBiasCurrent,Pin5

AllDevicesLM231/LM331LM231A/LM331A

VS=15V

0V≤VPIN5≤9.9VVPIN5=10VVPIN5MinTypMaxUnits%Full-Scale%Full-Scale%Full-Scale

±0.003±0.006±0.024

±0.01±0.02±0.14

VS=15V,f=10Hzto11kHzVIN=−10V,RS=14kΩ

0.950.90

TMIN≤TA≤TMAX,4.5V≤VS≤20V

1.001.00

1.051.10

kHz/VkHz/Vppm/˚Cppm/˚C%/V%/VkHz%Full-Scale%

±30±20

4.5V≤VS≤10V10V≤VS≤40VVIN=−10VTMIN≤TA≤TMAXVIN=−11V

1010.0

0.010.006

±150±50

0.10.06

±0.02

TMIN≤TA≤TMAXTMIN≤TA≤TMAX±3±4±3

−80

±10±14±10

−300

mVmVmVnAnAVxVSnAnAnA

±8

TMIN≤TA≤TMAX−0.20.63

0.667

±100

VCC−2.00.70

±10

200200

±100

1000500

=10V

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ElectricalCharacteristics

Parameter

TIMERVSATPIN5(Reset)

CURRENTSOURCE(Pin1)OutputCurrent

LM231,LM231ALM331,LM331AChangewithVoltage

CurrentSourceOFFLeakage

LM231,LM231A,LM331,LM331AAllDevices

OperatingRangeofCurrent(Typical)REFERENCEVOLTAGE(Pin2)LM231,LM231ALM331,LM331AStabilityvsTemperatureStabilityvsTime,1000HoursLOGICOUTPUT(Pin3)VSATOFFLeakageSUPPLYCURRENTLM231,LM231ALM331,LM331A

(Continued)

TA=25˚Cunlessotherwisespecified(Note2)

Conditions

I=5mA

RS=14kΩ,VPIN1=0

126116

0V≤VPIN1MinTyp0.22

Max0.5

UnitsV

1351360.20.02

1441561.010.050.0

µAµAµAnAnAµA

≤10V

TA=TMAX2.0(10to500)

1.761.70

1.1.

2.022.08

VDCVDCppm/˚C%

±60±0.1

I=5mA

I=3.2mA(2TTLLoads),TMIN≤TA≤TMAX0.150.10

0.500.401.04.06.06.08.0

VVµAmAmAmAmA

±0.05

VS=5VVS=40VVS=5VVS=40V

2.02.51.52.0

3.04.03.04.0

Note1:AbsoluteMaximumRatingsindicatelimitsbeyondwhichdamagetothedevicemayoccur.DCandACelectricalspecificationsdonotapplywhenoperatingthedevicebeyonditsspecifiedoperatingconditions.

Note2:AllspecificationsapplyinthecircuitofFigure4,with4.0V≤VS≤40V,unlessotherwisenoted.

Note3:NonlinearityisdefinedasthedeviationoffOUTfromVINx(10kHz/−10VDC)whenthecircuithasbeentrimmedforzeroerrorat10Hzandat10kHz,overthefrequencyrange1Hzto11kHz.Forthetimingcapacitor,CT,useNPOceramic,Teflon®,orpolystyrene.Note4:Humanbodymodel,100pFdischargedthrougha1.5kΩresistor.

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FunctionalBlockDiagram

DS005680-2

Pinnumbersapplyto8-pinpackagesonly.

FIGURE2.

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TypicalPerformanceCharacteristics

(AllelectricalcharacteristicsapplyforthecircuitofFigure4,unlessotherwisenoted.)NonlinearityErrorasPrecisionV-to-FConverter(Figure4)

NonlinearityError

NonlinearityErrorvsPowerSupplyVoltage

DS005680-26

DS005680-27

DS005680-25

FrequencyvsTemperatureVREFvsTemperature

OutputFrequencyvsVSUPPLYDS005680-28DS005680-29

DS005680-30

100kHzNonlinearityError(Figure5)NonlinearityError(Figure1)InputCurrent(Pins6,7)vsTemperature

DS005680-31DS005680-32

DS005680-33

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TypicalPerformanceCharacteristics

PowerDrainvsVSUPPLY(Continued)

NonlinearityError,PrecisionF-to-VConverter(Figure7)

OutputSaturationVoltagevsIOUT(Pin3)

DS005680-34

DS005680-35

DS005680-36

TypicalApplications

PRINCIPLESOFOPERATIONOFASIMPLIFIEDVOLTAGE-TO-FREQUENCYCONVERTER

TheLM231/331aremonolithiccircuitsdesignedforaccu-racyandversatileoperationwhenappliedasvoltage-to-frequency(V-to-F)convertersorasfrequency-to-voltage(F-to-V)converters.AsimplifiedblockdiagramoftheLM231/331isshowninFigure3andconsistsofaswitchedcurrentsource,inputcomparator,and1-shottimer.

TheoperationoftheseblocksisbestunderstoodbygoingthroughtheoperatingcycleofthebasicV-to-Fconverter,Figure3,whichconsistsofthesimplifiedblockdiagramoftheLM231/331andthevariousresistorsandcapacitorscon-nectedtoit.

Thevoltagecomparatorcomparesapositiveinputvoltage,V1,atpin7tothevoltage,Vx,atpin6.IfV1isgreater,thecomparatorwilltriggerthe1-shottimer.TheoutputofthetimerwillturnONboththefrequencyoutputtransistorandtheswitchedcurrentsourceforaperiodt=1.1RtCt.Duringthisperiod,thecurrentiwillflowoutoftheswitchedcurrentsourceandprovideafixedamountofcharge,Q=ixt,intothecapacitor,CL.ThiswillnormallychargeVxuptoahigherlevelthanV1.Attheendofthetimingperiod,thecurrentiwillturnOFF,andthetimerwillresetitself.

Nowthereisnocurrentflowingfrompin1,andthecapacitorCLwillbegraduallydischargedbyRLuntilVxfallstothelevelofV1.Thenthecomparatorwilltriggerthetimerandstartan-othercycle.

ThecurrentflowingintoCLisexactlyIAVE=ix(1.1xRtCt)xf,andthecurrentflowingoutofCLisexactlyVx/RL≅VIN/RL.IfVINisdoubled,thefrequencywilldoubletomaintainthisbalance.EvenasimpleV-to-Fconvertercanprovideafre-quencypreciselyproportionaltoitsinputvoltageoverawiderangeoffrequencies.

DS005680-4

FIGURE3.SimplifiedBlockDiagramofStand-Alone

Voltage-to-FrequencyConverterand

ExternalComponentsDETAILOFOPERATION,FUNCTIONALBLOCKDIAGRAM(Figure2)

Theblockdiagramshowsabandgapreferencewhichpro-videsastable1.9VDCoutput.This1.9VDCiswellregulatedoveraVSrangeof3.9Vto40V.Italsohasaflat,lowtem-peraturecoefficient,andtypicallychangeslessthan1⁄2%overa100˚Ctemperaturechange.

Thecurrentpumpcircuitforcesthevoltageatpin2tobeat1.9V,andcausesacurrenti=1.90V/RStoflow.ForRs=14k,i=135µA.Theprecisioncurrentreflectorprovidesacurrentequaltoitothecurrentswitch.Thecurrentswitchswitchesthecurrenttopin1ortogrounddependingonthestateoftheRSflip-flop.

ThetimingfunctionconsistsofanRSflip-flop,andatimercomparatorconnectedtotheexternalRtCtnetwork.Whentheinputcomparatordetectsavoltageatpin7higherthanpin6,itsetstheRSflip-flopwhichturnsONthecurrentswitchandtheoutputdrivertransistor.Whenthevoltageatpin5risesto2⁄3VCC,thetimercomparatorcausestheRSflip-floptoreset.TheresettransistoristhenturnedONandthecurrentswitchisturnedOFF.

However,iftheinputcomparatorstilldetectspin7higherthanpin6whenpin5crosses2⁄3VCC,theflip-flopwillnotbereset,andthecurrentatpin1willcontinuetoflow,initsat-tempttomakethevoltageatpin6higherthanpin7.This

6

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TypicalApplications

(Continued)

conditionwillusuallyapplyunderstart-upconditionsorinthecaseofanoverloadvoltageatsignalinput.Itshouldbenotedthatduringthissortofoverload,theoutputfrequencywillbe0;assoonasthesignalisrestoredtotheworkingrange,theoutputfrequencywillberesumed.

Theoutputdrivertransistoractstosaturatepin3withanONresistanceofabout50Ω.Incaseofovervoltage,theoutputcurrentisactivelylimitedtolessthan50mA.

Thevoltageatpin2isregulatedat1.90VDCforallvaluesofibetween10µAto500µA.Itcanbeusedasavoltageref-erenceforothercomponents,butcaremustbetakentoen-surethatcurrentisnottakenfromitwhichcouldreducetheaccuracyoftheconverter.

PRINCIPLESOFOPERATIONOFBASICVOLTAGE-TO-FREQUENCYCONVERTER(Figure1)

Thesimplestand-aloneV-to-FconvertershowninFigure1includesallthebasiccircuitryofFigure3plusafewcompo-nentsforimprovedperformance.

Aresistor,RIN=100kΩ±10%,hasbeenaddedinthepathtopin7,sothatthebiascurrentatpin7(−80nAtypical)willcanceltheeffectofthebiascurrentatpin6andhelpprovideminimumfrequencyoffset.

TheresistanceRSatpin2ismadeupofa12kΩfixedresis-torplusa5kΩ(cermet,preferably)gainadjustrheostat.ThefunctionofthisadjustmentistotrimoutthegaintoleranceoftheLM231/331,andthetoleranceofRt,RLandCt.Forbestresults,allthecomponentsshouldbestablelow-temperature-coefficientcomponents,suchasmetal-filmresistors.Thecapacitorshouldhavelowdielectricabsorp-tion;dependingonthetemperaturecharacteristicsdesired,NPOceramic,polystyrene,Teflonorpolypropylenearebestsuited.

AcapacitorCINisaddedfrompin7togroundtoactasafilterforVIN.Avalueof0.01µFto0.1µFwillbeadequateinmostcases;however,incaseswherebetterfilteringisrequired,a

1µFcapacitorcanbeused.WhentheRCtimeconstantsarematchedatpin6andpin7,avoltagestepatVINwillcauseastepchangeinfOUT.IfCINismuchlessthanCL,astepatVINmaycausefOUTtostopmomentarily.

A47Ωresistor,inserieswiththe1µFCL,isaddedtogivehysteresiseffectwhichhelpstheinputcomparatorprovidetheexcellentlinearity(0.03%typical).

DETAILOFOPERATIONOFPRECISIONV-TO-FCONVERTER(Figure4)

Inthiscircuit,integrationisperformedbyusingaconven-tionaloperationalamplifierandfeedbackcapacitor,CF.Whentheintegrator’soutputcrossesthenominalthresholdlevelatpin6oftheLM231/331,thetimingcycleisinitiated.Theaveragecurrentfedintotheopamp’ssummingpoint(pin2)isix(1.1RtCt)xfwhichisperfectlybalancedwith−VIN/RIN.Inthiscircuit,thevoltageoffsetoftheLM231/331inputcomparatordoesnotaffecttheoffsetoraccuracyoftheV-to-Fconverterasitdoesinthestand-aloneV-to-Fcon-verter;nordoestheLM231/331biascurrentoroffsetcur-rent.Instead,theoffsetvoltageandoffsetcurrentoftheop-erationalamplifieraretheonlylimitsonhowsmallthesignalcanbeaccuratelyconverted.Sinceopampswithvoltageoff-setwellbelow1mVandoffsetcurrentswellbelow2nAareavailableatlowcost,thiscircuitisrecommendedforbestac-curacyforsmallsignals.Thiscircuitalsorespondsimmedi-atelytoanychangeofinputsignal(whichastand-alonecir-cuitdoesnot)sothattheoutputfrequencywillbeanaccuraterepresentationofVIN,asquicklyas2outputpulses’spacingcanbemeasured.

Intheprecisionmode,excellentlinearityisobtainedbe-causethecurrentsource(pin1)isalwaysatgroundpotentialandthatvoltagedoesnotvarywithVINorfOUT.(Inthestand-aloneV-to-Fconverter,amajorcauseofnon-linearityistheoutputimpedanceatpin1whichcausesitochangeasafunctionofVIN).

ThecircuitofFigure5operatesinthesamewayasFigure4,butwiththenecessarychangesforhighspeedoperation.

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TypicalApplications

(Continued)

DS005680-5

*Usestablecomponentswithlowtemperaturecoefficients.SeeTypicalApplicationssection.**Thisresistorcanbe5kΩor10kΩforVS=8Vto22V,butmustbe10kΩforVS=4.5Vto8V.***UselowoffsetvoltageandlowoffsetcurrentopampsforA1:recommendedtypeLF411A

FIGURE4.StandardTestCircuitandApplicationsCircuit,PrecisionVoltage-to-FrequencyConverter

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TypicalApplications

(Continued)

DETAILSOFOPERATION,FREQUENCY-TO-VOLTAGECONVERTERS(Figure6andFigure7)

Intheseapplications,apulseinputatfINisdifferentiatedbyaC-Rnetworkandthenegative-goingedgeatpin6causestheinputcomparatortotriggerthetimercircuit.JustaswithaV-to-Fconverter,theaveragecurrentflowingoutofpin1isIAVERAGE=ix(1.1RtCt)xf.

InthesimplecircuitofFigure6,thiscurrentisfilteredinthenetworkRL=100kΩand1µF.Theripplewillbelessthan10mVpeak,buttheresponsewillbeslow,witha0.1secondtimeconstant,andsettlingof0.7secondto0.1%accuracy.

Intheprecisioncircuit,anoperationalamplifierprovidesabufferedoutputandalsoactsasa2-polefilter.Theripplewillbelessthan5mVpeakforallfrequenciesabove1kHz,andtheresponsetimewillbemuchquickerthaninFigure6.However,forinputfrequenciesbelow200Hz,thiscircuitwillhaveworseripplethanFigure6.Theengineeringofthefiltertime-constantstogetadequateresponseandsmallenoughripplesimplyrequiresastudyofthecompromisestobemade.Inherently,V-to-Fconverterresponsecanbefast,butF-to-Vresponsecannot.

DS005680-6

*Usestablecomponentswithlowtemperaturecoefficients.SeeTypicalApplicationssection.

**Thisresistorcanbe5kΩor10kΩforVS=8Vto22V,butmustbe10kΩforVS=4.5Vto8V.

***UselowoffsetvoltageandlowoffsetcurrentopampsforA1:recommendedtypesLF411AorLF356.

FIGURE5.PrecisionVoltage-to-FrequencyConverter,

100kHzFull-Scale,±0.03%Non-Linearity

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TypicalApplications

(Continued)

DS005680-7

DS005680-8

*Usestablecomponentswithlowtemperaturecoefficients.

FIGURE6.SimpleFrequency-to-VoltageConverter,

10kHzFull-Scale,±0.06%Non-Linearity

*Usestablecomponentswithlowtemperaturecoefficients.

FIGURE7.PrecisionFrequency-to-VoltageConverter,

10kHzFull-Scalewith2-PoleFilter,±0.01%

Non-LinearityMaximum

LightIntensitytoFrequencyConverter

DS005680-9

*L14F-1,L14G-1orL14H-1,phototransistor(GeneralElectricCo.)orsimilar

TemperaturetoFrequencyConverter

DS005680-10

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TypicalApplications

(Continued)

BasicAnalog-to-DigitalConverterUsing

Voltage-to-FrequencyConverter

Long-TermDigitalIntegratorUsingVFC

DS005680-11

DS005680-12

Analog-to-DigitalConverterwithMicroprocessor

DS005680-13

RemoteVoltage-to-FrequencyConverterwith2-WireTransmitterandReceiver

DS005680-14

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TypicalApplications

(Continued)

Voltage-to-FrequencyConverterwithSquare-WaveOutputUsing÷2Flip-Flop

DS005680-15

Voltage-to-FrequencyConverterwithIsolators

DS005680-16

Voltage-to-FrequencyConverterwithIsolators

DS005680-17

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TypicalApplications

(Continued)

Voltage-to-FrequencyConverterwithIsolators

DS005680-18

Voltage-to-FrequencyConverterwithIsolators

DS005680-19

ConnectionDiagram

Dual-In-LinePackage

DS005680-21

OrderNumberLM231AN,LM231N,LM331AN,

orLM331N

SeeNSPackageNumberN08E

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SchematicDiagram

DS005680-22www.national.com14

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LM231A/LM231/LM331A/LM331PrecisionVoltage-to-FrequencyConvertersPhysicalDimensions

inches(millimeters)unlessotherwisenoted

Dual-In-LinePackage(N)

OrderNumberLM231AN,LM231N,LM331AN,orLM331N

NSPackageN08E

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