LMx31x Precision Voltage-to-Frequency Converters (Rev. C)

1 ProductFolderSample &BuyTechnicalDocumentsTools &SoftwareSupport &CommunityLM231,LM331 SNOSBI2C JUNE1999 REVISEDSEPTEMBER2015 LMx31xPrecisionVoltage-to-FrequencyConve rters1 Features3 DescriptionThe LMx31familyof voltage -to-frequencyconverters1 ideallysuitedfor use in simplelow-costcircuits ImprovedPerformancein ExistingVoltage-to-for analog-to-digitalconversion,precisionfre quency-FrequencyConversionApplicationsto -voltageconversion,long-termintegration, linear Splitor Single-SupplyOperationfrequencymodulatio nor demodulation, outputwhenusedas a voltage - Operateson Single5-V Supplyto-frequencyconverteris a pulsetrainat a frequency PulseOutputCompatibleWithAll LogicFormspreciselyproportionalto the appliedinputvoltage. ExcellentTemperatureStability: 50 ppm/ CThus,it providesall the inherentadvantagesof theMaximumvoltage-to-frequencyconversion techniques,andiseasyto applyin all standardvoltage-to- frequency Low PowerConsumption:15 mW Typicalat 5 Vconverterapplications. WideDynamicRange,100 dB Minimumat 10-kHzFull ScaleFrequencyDeviceInformation(1) WideRangeof Full ScaleFrequency:PARTNUMBERPACKAGEBODYSIZE (NOM)1 Hz to 100 kHzLM231 PDIP(8) Low-CostLM331(1) For all availablepackages,see the orderableaddendumat2 Applicationsthe end of the datasheet.

2 Voltageto FrequencyConversions Frequencyto VoltageConversions Remote-SensorMonitoring TachometersSchematicDiagram1An IMPORTANTNOTICEat the end of this datasheetaddressesavailability,warranty, changes,use in safety-criticalapplications,intellectual propertymattersand ,LM331 SNOSBI2C JUNE1999 Applicationand Pin Configurationand Deviceand Mechanical,Packaging,and RevisionHistoryNOTE:Pagenumbersfor previousrevisionsmay differfrompagenumbersin the (March2013)to RevisionCPage AddedPin Configurationand Functionssection,ESDR atingstable,FeatureDescriptionsection,De viceFunctionalModes,Applicationand Implementationsection,PowerSupplyRecomme ndationssection,Layoutsection,Deviceand DocumentationSupportsection,andMechanica l,Packaging,and (March2013)to RevisionBPage Changedlayoutof NationalDataSheetto TI 1999 2015,TexasInstrumentsIncorporatedProduct FolderLinks:LM231LM331LM231, JUNE1999 REVISEDSEPTEMBER20155 DescriptioncontinuedFurther,the LMx31 Aattaina new highlevelof accuracyversustemperaturewhichcouldonly be LMx31are ideallysuitedfor use in digitalsystemsatlow powersupplyvoltagesand can providelow-costanalog-to-digitalconversi onin ,the frequencyfroma battery-poweredvoltage-to-frequencyconve rtercan be easilychanneledthrougha simplephotoisolatorto provideisolationagainsthigh LMx31usesa new temperature-compensatedband-gapreference circuit,to provideexcellentaccuracyoverthe full operatingtemperaturerange,at powersuppliesas low as 4 V.

3 The precisiontimercircuithas low biascurrentswithoutdegradingthe quickresponsenecessaryfor theoutputare capableof driving3 TTL loads,or a high-voltageoutputup to 40 V, yet is 1999 2015,TexasInstrumentsIncorporatedSubmitD ocumentationFeedback3 ProductFolderLinks:LM231LM331LM231,LM331 SNOSBI2C JUNE1999 Pin Configurationand FunctionsP Package8-PinPDIPTop ViewPin outputis an open-collectoroutputand requiresa filter inputTHRESH6 IThresholdinputCOMPIN7 IComparatorInputVS8 PSupplyVoltage7 (1)(2)(3)MINMAXUNITS upplyVoltage,VS40 VOutputShortCircuitto GroundContinuousOutputShortCircuitto VCCC ontinuousInputVoltage +VSVLeadTemperature(Soldering,10 sec.)PDIP260 C(1)StressesbeyondthoselistedunderAbsolu teMaximumRatingsmay causepermanentdamageto the stressratingsonly,whichdo not implyfunctionaloperationof the deviceat theseor any otherconditionsbeyondthoseindicatedunder RecommendedOperatingConditions. Exposureto absolute-maximum-ratedconditionsfor extendedperiodsmay affectdevicereliability.

4 (2)All voltagesare measuredwith respectto GND= 0 V, unlessotherwisenoted.(3)If Military/Aerospacespecifieddevicesare required,pleasecontactthe TI SalesOffice/Distributorsfor availabilityand (ESD)ElectrostaticdischargeHumanbodymode l(HBM),per ANSI/ESDA/JEDECJS-001(1)(2) 500V(1)JEDEC documentJEP155statesthat 500-VHBM allowssafe manufacturingwith a standardESDcontrolprocess.(2)Humanbodymo del,100 pF dischargedthrougha 1999 2015,TexasInstrumentsIncorporatedProduct FolderLinks:LM231LM331LM231, JUNE1999 ,LM231A 2585 COperatingAmbientTemperatureLM331,LM331A 070 CSupplyVoltage,VS(1)440V(1)All voltagesare measuredwith respectto GND= 0 V, ,LM331 THERMALMETRIC(1)P (PDIP)UNIT8 PINSR JAJunction-to-ambientthermalresistance10 0 C/W(1)For moreinformationabouttraditionaland new thermalmetrics,see theSemiconductorand IC PackageThermalMetricsapplicationreport, specificationsapplyin the circuitof Figure16, with V VS 40 V, TA= 25 C, V VS 20 V (1)% Full-TMIN TA TMAX Circuitof Figure14VS= 15 V, f = 10 Hz to 11 kHz ,LM231 AVIN= 10 V, RS= 14 k (Gain)LM331, TA TMAXLMx31 30 150ppm/ V VS 20 Vof GainLMx31A 20 50ppm/ V VS 10 Gainwith VS10 V VS 40 10 Full-GainStabilityvs.

5 Time(1000 Hours)TMIN TA TMAX (BeyondFull-Scale)FrequencyVIN= 11 V10%INPUTCOMPARATORO ffsetVoltage 3 10mVLM231/LM331 TMIN TA TMAX 4 14mVLM231A/LM331 ATMIN TA TMAX 3 10mVBiasCurrent 80 300nAOffsetCurrent 8 100nACommon-ModeRangeTMIN TA TMAX 2 VTIMERT imerThresholdVoltage,Pin VSInputBiasCurrent,Pin 5VS= 15 VAll Devices0V VPIN 5 V 10 100nALM231/LM331 VPIN 5= 10 V2001000nALM231A/LM331 AVPIN 5= 10 V200500nAVSATPIN 5(Reset)I = 5 (1)Non-linearityis definedas the deviationof fOUTfromVIN (10 kHz/ 10 VDC) whenthe circuithas beentrimmedfor zeroerrorat 10 Hzand at 10 kHz,overthe frequencyrange1 Hz to 11 the timingcapacitor,CT, use NPOceramic,Teflon , or 1999 2015,TexasInstrumentsIncorporatedSubmitD ocumentationFeedback5 ProductFolderLinks:LM231LM331LM231,LM331 SNOSBI2C JUNE1999 (continued)All specificationsapplyin the circuitof Figure16, with V VS 40 V, TA= 25 C, (PIN1)LM231,LM231 ARS= 14 k , VPIN 1= 0126135144 AOutputCurrentLM331,LM331A116136156 AChangewith Voltage0V VPIN 1 10 ALM231,LM231A, ,LM331 ALeakageAll DevicesTA= TMAX250nAOperatingRangeof Current(Typical)(10 to 500) AREFERENCEVOLTAGE(PIN2)LM231, , Temperature 60ppm/ CStabilityvs.

6 Time,1000 Hours (PIN3)I = 5 = mA (2 TTL Loads), TA TMAXOFFL eakage ASUPPLYCURRENTVS= 5 V234mALM231,LM231 AVS= 40 5 ,LM331 AVS= 40 25 C(1) (1)The absolutemaximumjunctiontemperature(TJmax )for this deviceis 150 C. The maximumallowablepowerdissipationis dictatedbyTJmax,the junction-to-ambientthermalresistance( JA), and the ambienttemperatureTA, and can be calculatedusingthe formulaPDmax = (TJmax - TA) / JA. The valuesfor maximumpowerdissipationwill be reachedonly whenthe deviceis operatedin a severefault condition( ,wheninputor outputpins are drivenbeyondthe powersupplyvoltages,or the powersupplypolarityis reversed).Obviously,suchconditionsshould alwaysbe 1999 2015,TexasInstrumentsIncorporatedProduct FolderLinks:LM231LM331LM231, JUNE1999 (All electricalcharacteristicsapplyfor the circuitof Figure16, unlessotherwisenoted.)Figure1. Non-LinearityErroras PrecisionV-to-FConverterFigure2. Non-LinearityError(Figure16)Figure4. Frequencyvs. TemperatureFigure3. Non-LinearityErrorvs.

7 PowerSupplyVoltageFigure6. OutputFrequencyvs. VSUPPLYF igure5. VREFvs. TemperatureCopyright 1999 2015,TexasInstrumentsIncorporatedSubmitD ocumentationFeedback7 ProductFolderLinks:LM231LM331LM231,LM331 SNOSBI2C JUNE1999 (continued)(All electricalcharacteristicsapplyfor the circuitof Figure16, unlessotherwisenoted.)Figure8. Non-LinearityError(Figure14)Figure7. 100 kHz Non-LinearityError(Figure17)Figure9. InputCurrent(Pins6,7) vs. TemperatureFigure10. PowerDrainvs. VSUPPLYF igure12. Non-LinearityError,PrecisionF-to-VConver terFigure11. OutputSaturationVoltagevs. IOUT(Pin 3)(Figure19)8 SubmitDocumentationFeedbackCopyright 1999 2015,TexasInstrumentsIncorporatedProduct FolderLinks:LM231LM331LM231, JUNE1999 REVISEDSEPTEMBER20158 Operation,FunctionalBlockDiagramTheFunct ionalBlockDiagramshowsa bandgap referencewhichprovidesa VDCis well regulatedovera VSrangeof V to 40 V. It also has a flat, low temperaturecoefficient,and typicallychangesless than % overa 100 C currentpumpcircuitforcesthe voltageat pin 2 to be at V, and causesa currenti = RS=14 k, i=135 A.

8 The precisioncurrentreflectorprovidesa currentequalto i to the currentto pin 1 or to ground,dependinguponthe stateof the R-S timingfunctionconsistsof an R-S flip-flopand a timercomparatorconnectedto the inputcomparatordetectsa voltageat pin 7 higherthanpin 6, it sets the R-S flip-flopwhichturnsONthe currentswitchand the voltageat pin 5 risesto VCC, the timercomparatorcausesthe R-S flip-flopto resettransistoris thenturnedON and the currentswitchis ,if the inputcomparatorstill detectsthe voltageon pin 7 as higherthanpin 6 whenpin 5 crosses VCC, the flip-flopwill not be reset,and the currentat pin 1 will continueto flow,tryingto makethe voltageat pin 6higherthanpin 7. This conditionwill usuallyapplyunderstart-upconditionsor in the caseof an overloadvoltageat sort of overloadthe outputfrequencywill be 0. As soonas the signalis restoredto theworkingrange,the outputfrequencywill be 1999 2015,TexasInstrumentsIncorporatedSubmitD ocumentationFeedback9 ProductFolderLinks:LM231LM331LM231,LM331 SNOSBI2C JUNE1999 LMx31operateovera widevoltagerangeof 4 V to 40 voltageat pin 2 is regulatedat all valuesof i between10 A to 500 A.

9 It can be usedas avoltagereferencefor othercomponents,but takecareto ensurethat currentis not takenfromit whichcouldreducethe accuracyof the outputdrivertransistoracts to saturatepin 3 with an ON resistanceof about50 . In caseof overvoltage,the outputcurrentis activelylimitedto less than50 the voltageon pin 7 is higherthanpin 6 whenpin 5 crosses VCC, the LMx31internalflip-flopwill not bereset,and the currentat pin 1 will continueto flow,tryingto makethe voltageat pin 6 higherthanpin 7. Thisconditionwill usuallyapplyunderstart-upconditionsor in the caseof an overloadvoltageat sort of overloadthe outputfrequencywill be 0. As soonas the signalis restoredto the workingrange,theoutputfrequencywill be 1999 2015,TexasInstrumentsIncorporatedProduct FolderLinks:LM231LM331LM231, JUNE1999 REVISEDSEPTEMBER20159 Applicationand ImplementationNOTEI nformationin the followingapplicationssectionsis not partof the TI componentspecification,and TI doesnot warrantits accuracyor s customersareresponsiblefor determiningsuitabilityof componentsfor test theirdesignimplementationto theseblocksis bestunderstoodby goingthroughthe operatingcycleof the basicV-to-Fconverter,Figure13, whichconsistsof the simplifiedblockdiagramof the LMx31and the variousresistorsandcapacitorsconnectedto voltagecomparatorcomparesa positiveinputvoltage,V1, at pin 7 to the voltage ,Vx, at pin 6.

10 If V1 isgreater,the comparatorwill triggerthe outputof the timerwill turn ON boththe frequencyoutputtransistorand the switchedcurrentsourcefor a periodt = RtCt. Duringthis period,the currenti willflow out of the switchedcurrentsourceand providea fixedamountof charge,Q = i t, into the capacitor, normallychargeVxup to a higherlevelthanV1. At the end of the timingperiod,the currenti will turnOFF,and the timerwill no currentflowingfrompin 1, and the capacitorCLwill be graduallydischargedby RLuntil Vxfallsto the levelof V1. Thenthe comparatorwill triggerthe timerand currentflowinginto CLis exactlyIAVE= i ( RtCt) f, and the currentflowingout of CLis exactlyVx/RL VIN/RL. If VINis doubled,the frequencywill doubleto maintainthis simpleV-to-Fconvertercanprovidea frequencypreciselyproportionalto its inputvoltageovera widerangeof OperationThe LMx31are monolithiccircuitsdesignedfor accuracyand versatileoperationwhenappliedas Voltage-to-Frequency (V-to-F)convertersor as frequency -to- voltage (F-to-V) simplifiedblockdiagramof theLMx31is shownin Figure13 and consistsof a switchedcurrentsource,inputcomparator,an d SimplifiedBlockDiagramof Stand-AloneVoltage-to-FrequencyConverter andExternalComponentsCopyright 1999 2015,TexasInstrumentsIncorporatedSubmitD ocumentationFeedback11 ProductFolderLinks:LM231LM331LM231,LM331 SNOSBI2C JUNE1999 simplestand-aloneV-to-Fconvertershownin Figure14 includesall the basiccircuitryof Figure13 plus afew componentsfor improvedperformance.