LM3914Dot/BarDisplayDriverJanuary2000
LM3914
Dot/BarDisplayDriver
GeneralDescription
TheLM3914isamonolithicintegratedcircuitthatsensesanalogvoltagelevelsanddrives10LEDs,providingalinearanalogdisplay.Asinglepinchangesthedisplayfromamov-ingdottoabargraph.CurrentdrivetotheLEDsisregulatedandprogrammable,eliminatingtheneedforresistors.Thisfeatureisonethatallowsoperationofthewholesystemfromlessthan3V.
Thecircuitcontainsitsownadjustablereferenceandaccu-rate10-stepvoltagedivider.Thelow-bias-currentinputbufferacceptssignalsdowntoground,orV−,yetneedsnoprotectionagainstinputsof35Vaboveorbelowground.Thebufferdrives10individualcomparatorsreferencedtotheprecisiondivider.Indicationnon-linearitycanthusbeheldtypicallyto1⁄2%,evenoverawidetemperaturerange.
VersatilitywasdesignedintotheLM3914sothatcontroller,visualalarm,andexpandedscalefunctionsareeasilyaddedontothedisplaysystem.ThecircuitcandriveLEDsofmanycolors,orlow-currentincandescentlamps.ManyLM3914scanbe“chained”toformdisplaysof20toover100seg-ments.Bothendsofthevoltagedividerareexternallyavail-ablesothat2driverscanbemadeintoazero-centermeter.TheLM3914isveryeasytoapplyasananalogmetercircuit.A1.2Vfull-scalemeterrequiresonly1resistorandasingle3Vto15Vsupplyinadditiontothe10displayLEDs.Ifthe1resistorisapot,itbecomestheLEDbrightnesscontrol.Thesimplifiedblockdiagramillustratesthisextremelysimpleex-ternalcircuitry.
Wheninthedotmode,thereisasmallamountofoverlapor“fade”(about1mV)betweensegments.ThisassuresthatatnotimewillallLEDsbe“OFF”,andthusanyambiguousdis-playisavoided.Variousnoveldisplaysarepossible.
Muchofthedisplayflexibilityderivesfromthefactthatalloutputsareindividual,DCregulatedcurrents.Variouseffectscanbeachievedbymodulatingthesecurrents.Theindi-vidualoutputscandriveatransistoraswellasaLEDatthesametime,socontrollerfunctionsincluding“staging”controlcanbeperformed.TheLM3914canalsoactasaprogram-mer,orsequencer.
TheLM3914isratedforoperationfrom0˚Cto+70˚C.TheLM3914N-1isavailableinan18-leadmolded(N)package.Thefollowingtypicalapplicationillustratesadjustingofthereferencetoadesiredvalue,andpropergroundingforaccu-rateoperation,andavoidingoscillations.
Features
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DrivesLEDs,LCDsorvacuumfluorescents
BarordotdisplaymodeexternallyselectablebyuserExpandabletodisplaysof100steps
Internalvoltagereferencefrom1.2Vto12VOperateswithsinglesupplyoflessthan3VInputsoperatedowntoground
Outputcurrentprogrammablefrom2mAto30mANomultiplexswitchingorinteractionbetweenoutputsInputwithstands±35VwithoutdamageorfalseoutputsLEDdriveroutputsarecurrentregulated,open-collectors
nOutputscaninterfacewithTTLorCMOSlogicnTheinternal10-stepdividerisfloatingandcanbereferencedtoawiderangeofvoltages
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LM3914TypicalApplications
0Vto5VBarGraphMeter
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Note:Groundingmethodistypicalofalluses.The2.2µFtantalumor10µFaluminumelectrolyticcapacitorisneededifleadstotheLEDsupplyare6\"orlonger.
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LM3914AbsoluteMaximumRatings(Note1)
IfMilitary/Aerospacespecifieddevicesarerequired,pleasecontacttheNationalSemiconductorSalesOffice/Distributorsforavailabilityandspecifications.PowerDissipation(Note6)MoldedDIP(N)SupplyVoltage
VoltageonOutputDrivers
InputSignalOvervoltage(Note4)DividerVoltage
1365mW
25V25V±35V
−100mVtoV+ReferenceLoadCurrent10mAStorageTemperatureRange−55˚Cto+150˚CSolderingInformationDual-In-LinePackageSoldering(10seconds)260˚CPlasticChipCarrierPackageVaporPhase(60seconds)215˚CInfrared(15seconds)220˚CSeeAN-450“SurfaceMountingMethodsandTheirEffectonProductReliability”forothermethodsofsolderingsurfacemountdevices.
ElectricalCharacteristics(Notes2,4)
Parameter
COMPARATOR
OffsetVoltage,BufferandFirstComparator
OffsetVoltage,BufferandAnyOtherComparatorGain(∆ILED/∆VIN)
InputBiasCurrent(atPin5)InputSignalOvervoltageVOLTAGE-DIVIDERDividerResistanceAccuracy
VOLTAGEREFERENCEOutputVoltageLineRegulationLoadRegulation
OutputVoltageChangewithTemperatureAdjustPinCurrentOUTPUTDRIVERSLEDCurrent
LEDCurrentDifference(BetweenLargestandSmallestLEDCurrents)LEDCurrentRegulationDropoutVoltageSaturationVoltage
OutputLeakage,EachCollectorOutputLeakageSUPPLYCURRENTStandbySupplyCurrent(AllOutputsOff)
V+=5V,
IL(REF)=0.2mAV+=20V,
IL(REF)=1.0mA
2.46.1
4.29.2
mAmA
V+=VLED=5V,IL(REF)=1mA
ILED=2mAVLED=5V2V≤VLED≤17V
ILED=20mAILED=2mAILED=20mA
7
100.121.20.11
130.430.2531.5
0.150.1
Pins10–18Pin1
60
0.1150
0.41010450
mAmAmAVVµAµAµA
0.1mA≤IL(REF)≤4mA,V+=VLED=5V3V≤V+≤18V
0.1mA≤IL(REF)≤4mA,V+=VLED=5V
0˚C≤TA≤+70˚C,IL(REF)=1mA,V+=5V
1.2
1.280.010.4175
1201.340.032
V%/V%%µA
Total,Pin6to4(Note3)
8
120.5
172
kΩ%
0V≤VRLO=VRHI≤12V,ILED=1mA
0V≤VRLO=VRHI≤12V,ILED=1mA
IL(REF)=2mA,ILED=10mA0V≤VIN≤V−1.5VNoChangeinDisplay
−35
+Conditions(Note2)MinTypMaxUnits
33
3
825
1015
mVmVmA/mV
10035
nAV
ILED(ON)=20mA,VLED=5V,∆ILED=2mA
ILED=2.0mA,IL(REF)=0.4mA(BarMode)(Note5)(DotMode)(Note5)
Note1:AbsoluteMaximumRatingsindicatelimitsbeyondwhichdamagetothedevicemayoccur.OperatingRatingsindicateconditionsforwhichthedeviceisfunc-tional,butdonotguaranteespecificperformancelimits.ElectricalCharacteristicsstateDCandACelectricalspecificationsunderparticulartestconditionswhichguar-anteespecificperformancelimits.ThisassumesthatthedeviceiswithintheOperatingRatings.Specificationsarenotguaranteedforparameterswherenolimitisgiven,however,thetypicalvalueisagoodindicationofdeviceperformance.
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LM3914ElectricalCharacteristics(Notes2,4)
3VDC≤V+≤20VDC3VDC≤VLED≤V+
VREF,VRHI,VRLO≤(V+−1.5V)0V≤VIN≤V+−1.5V
(Continued)
Note2:Unlessotherwisestated,allspecificationsapplywiththefollowingconditions:
−0.015V≤VRLO≤12VDC−0.015V≤VRHI≤12VDC
TA=+25˚C,IL(REF)=0.2mA,VLED=3.0V,pin9connectedtopin3(BarMode).
Forhigherpowerdissipations,pulsetestingisused.
Note3:Accuracyismeasuredreferredto+10.000VDCatpin6,with0.000VDCatpin4.Atlowerfull-scalevoltages,bufferandcomparatoroffsetvoltagemayaddsignificanterror.
Note4:Pin5inputcurrentmustbelimitedto±3mA.Theadditionofa39kresistorinserieswithpin5allows±100Vsignalswithoutdamage.
Note5:Barmoderesultswhenpin9iswithin20mVofV+.Dotmoderesultswhenpin9ispulledatleast200mVbelowV+orleftopencircuit.LEDNo.10(pin10outputcurrent)isdisabledifpin9ispulled0.9VormorebelowVLED.
Note6:ThemaximumjunctiontemperatureoftheLM3914is100˚C.Devicesmustbederatedforoperationatelevatedtemperatures.Junctiontoambientthermalresistanceis55˚C/WforthemoldedDIP(Npackage).
DefinitionofTerms
Accuracy:Thedifferencebetweentheobservedthresholdvoltageandtheidealthresholdvoltageforeachcomparator.Specifiedandtestedwith10Vacrosstheinternalvoltagedi-vidersothatresistorratiomatchingerrorpredominatesovercomparatoroffsetvoltage.
AdjustPinCurrent:Currentflowingoutofthereferencead-justpinwhenthereferenceamplifierisinthelinearregion.ComparatorGain:Theratioofthechangeinoutputcurrent(ILED)tothechangeininputvoltage(VIN)requiredtopro-duceitforacomparatorinthelinearregion.
DropoutVoltage:Thevoltagemeasuredatthecurrentsourceoutputsrequiredtomaketheoutputcurrentfallby10%.
InputBiasCurrent:Currentflowingoutofthesignalinputwhentheinputbufferisinthelinearregion.
LEDCurrentRegulation:ThechangeinoutputcurrentoverthespecifiedrangeofLEDsupplyvoltage(VLED)asmeasuredatthecurrentsourceoutputs.Astheforwardvolt-ageofanLEDdoesnotchangesignificantlywithasmallchangeinforwardcurrent,thisisequivalenttochangingthevoltageattheLEDanodesbythesameamount.
LineRegulation:Theaveragechangeinreferenceoutputvoltageoverthespecifiedrangeofsupplyvoltage(V+).LoadRegulation:Thechangeinreferenceoutputvoltage(VREF)overthespecifiedrangeofloadcurrent(IL(REF)).OffsetVoltage:Thedifferentialinputvoltagewhichmustbeappliedtoeachcomparatortobiastheoutputinthelinearre-gion.Mostsignificanterrorwhenthevoltageacrossthein-ternalvoltagedividerissmall.Specifiedandtestedwithpin6voltage(VRHI)equaltopin4voltage(VRLO).
TypicalPerformanceCharacteristics
SupplyCurrentvsTemperature
OperatingInputBiasCurrentvsTemperature
ReferenceVoltagevsTemperature
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LM3914TypicalPerformanceCharacteristics
ReferenceAdjustPinCurrentvsTemperature
(Continued)
LEDCurrent-RegulationDropout
LEDDriverSaturationVoltage
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InputCurrentBeyondSignalRange(Pin5)
LEDCurrentvsReferenceLoading
LEDDriverCurrentRegulation
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TotalDividerResistancevsTemperature
Common-ModeLimitsOutputCharacteristics
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LM3914BlockDiagram
(ShowingSimplestApplication)
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LM3914FunctionalDescription
ThesimplifedLM3914blockdiagramistogivethegeneralideaofthecircuit’soperation.Ahighinputimpedancebufferoperateswithsignalsfromgroundto12V,andisprotectedagainstreverseandovervoltagesignals.Thesignalisthenappliedtoaseriesof10comparators;eachofwhichisbi-asedtoadifferentcomparisonlevelbytheresistorstring.Intheexampleillustrated,theresistorstringisconnectedtotheinternal1.25Vreferencevoltage.Inthiscase,foreach125mVthattheinputsignalincreases,acomparatorwillswitchonanotherindicatingLED.Thisresistordividercanbeconnectedbetweenany2voltages,providingthattheyare1.5VbelowV+andnolessthanV−.Ifanexpandedscalemeterdisplayisdesired,thetotaldividervoltagecanbeaslittleas200mV.Expanded-scalemeterdisplaysaremoreaccurateandthesegmentslightuniformlyonlyifbarmodeisused.At50mVormoreperstep,dotmodeisusable.INTERNALVOLTAGEREFERENCE
Thereferenceisdesignedtobeadjustableanddevelopsanominal1.25VbetweentheREFOUT(pin7)andREFADJ(pin8)terminals.ThereferencevoltageisimpressedacrossprogramresistorR1and,sincethevoltageisconstant,aconstantcurrentI1thenflowsthroughtheoutputsetresistorR2givinganoutputvoltageof:
MODEPINUSE
Pin9,theModeSelectinputcontrolschainingofmultipleLM3914s,andcontrolsbarordotmodeoperation.Thefol-lowingtabulationshowsthebasicwaysofusingthisinput.Othermorecomplexuseswillbeillustratedintheapplica-tions.
BarGraphDisplay:WireModeSelect(pin9)directlytopin3(V+pin).
DotDisplay,SingleLM3914Driver:LeavetheModeSelectpinopencircuit.
DotDisplay,20orMoreLEDs:Connectpin9ofthefirstdriverintheseries(i.e.,theonewiththelowestinputvoltagecomparisonpoints)topin1ofthenexthigherLM3914driver.Continueconnectingpin9oflowerinputdriverstopin1ofhigherinputdriversfor30,40,ormoreLEDdisplays.ThelastLM3914driverinthechainwillhavepin9wiredtopin11.Allpreviousdriversshouldhavea20kresistorinparallelwithLEDNo.9(pin11toVLED).
ModePinFunctionalDescription
Thispinactuallyperformstwofunctions.Refertothesimpli-fiedblockdiagrambelow.
BlockDiagramofModePinDescription
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Sincethe120µAcurrent(max)fromtheadjustterminalrep-resentsanerrorterm,thereferencewasdesignedtomini-mizechangesofthiscurrentwithV+andloadchanges.CURRENTPROGRAMMING
AfeaturenotcompletelyillustratedbytheblockdiagramistheLEDbrightnesscontrol.Thecurrentdrawnoutoftheref-erencevoltagepin(pin7)determinesLEDcurrent.Approxi-mately10timesthiscurrentwillbedrawnthrougheachlightedLED,andthiscurrentwillberelativelyconstantde-spitesupplyvoltageandtemperaturechanges.Currentdrawnbytheinternal10-resistordivider,aswellasbytheex-ternalcurrentandvoltage-settingdividershouldbeincludedincalculatingLEDdrivecurrent.TheabilitytomodulateLEDbrightnesswithtime,orinproportiontoinputvoltageandothersignalscanleadtoanumberofnoveldisplaysorwaysofindicatinginputovervoltages,alarms,etc.
DS007970-5
*Highforbar
DOTORBARMODESELECTION
Thevoltageatpin9issensedbycomparatorC1,nominallyreferencedto(V+−100mV).Thechipisinbarmodewhenpin9isabovethislevel;otherwiseit’sindotmode.Thecom-paratorisdesignedsothatpin9canbeleftopencircuitfordotmode.
Takingintoaccountcomparatorgainandvariationinthe100mVreferencelevel,pin9shouldbenomorethan20mVbelowV+forbarmodeandmorethan200mVbelowV+(oropencircuit)fordotmode.Inmostapplications,pin9isei-theropen(dotmode)ortiedtoV+(barmode).Inbarmode,pin9shouldbeconnecteddirectlytopin3.Largecurrentsdrawnfromthepowersupply(LEDcurrent,forexample)shouldnotsharethispathsothatlargeIRdropsareavoided.DOTMODECARRY
InorderforthedisplaytomakesensewhenmultipleLM3914sarecascadedindotmode,specialcircuitryhasbeenincludedtoshutoffLEDNo.10ofthefirstdevicewhen
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LM3914ModePinFunctionalDescription
(Continued)
LEDNo.1oftheseconddevicecomeson.Theconnectionforcascadingindotmodehasalreadybeendescribedandisdepictedbelow.
AslongastheinputsignalvoltageisbelowthethresholdofthesecondLM3914,LEDNo.11isoff.Pin9ofLM3914No.1thusseeseffectivelyanopencircuitsothechipisindotmode.Assoonastheinputvoltagereachesthethresh-oldofLEDNo.11,pin9ofLM3914No.1ispulledanLEDdrop(1.5Vormore)belowVLED.ThisconditionissensedbycomparatorC2,referenced600mVbelowVLED.ThisforcestheoutputofC2low,whichshutsoffoutputtransistorQ2,ex-tinguishingLEDNo.10.
VLEDissensedviathe20kresistorconnectedtopin11.Theverysmallcurrent(lessthan100µA)thatisdivertedfromLEDNo.9doesnotnoticeablyaffectitsintensity.
Anauxiliarycurrentsourceatpin1keepsatleast100µAflowingthroughLEDNo.11eveniftheinputvoltageriseshighenoughtoextinguishtheLED.Thisensuresthatpin9ofLM3914No.1isheldlowenoughtoforceLEDNo.10offwhenanyhigherLEDisilluminated.While100µAdoesnotnormallyproducesignificantLEDillumination,itmaybeno-ticeablewhenusinghigh-efficiencyLEDsinadarkenviron-ment.Ifthisisbothersome,thesimplecureistoshuntLEDNo.11witha10kresistor.The1VIRdropismorethanthe900mVworstcaserequiredtoholdoffLEDNo.10yetsmallenoughthatLEDNo.11doesnotconductsignificantly.OTHERDEVICECHARACTERISTICS
TheLM3914isrelativelylow-powereditself,andsinceanynumberofLEDscanbepoweredfromabout3V,itisaveryefficientdisplaydriver.Typicalstandbysupplycurrent(all
LEDsOFF)is1.6mA(2.5mAmax).However,anyreferenceloadingadds4timesthatcurrentdraintotheV+(pin3)sup-plyinput.Forexample,anLM3914witha1mAreferencepinload(1.3k),wouldsupplyalmost10mAtoeveryLEDwhiledrawingonly10mAfromitsV+pinsupply.Atfull-scale,theICistypicallydrawinglessthan10%ofthecurrentsuppliedtothedisplay.
Thedisplaydriverdoesnothavebuilt-inhysteresissothatthedisplaydoesnotjumpinstantlyfromoneLEDtothenext.Underrapidlychangingsignalconditions,thiscutsdownhighfrequencynoiseandoftenanannoyingflicker.An“over-lap”isbuiltinsothatatnotimebetweensegmentsareallLEDscompletelyOFFinthedotmode.Generally1LEDfadesinwhiletheotherfadesoutoveramVormoreofrange(Note3).Thechangemaybemuchmorerapidbe-tweenLEDNo.10ofonedeviceandLEDNo.1ofaseconddevice“chained”tothefirst.
TheLM3914featuresindividuallycurrentregulatedLEDdrivertransistors.Furtherinternalcircuitrydetectswhenanydrivertransistorgoesintosaturation,andpreventsothercir-cuitryfromdrawingexcesscurrent.ThisresultsintheabilityoftheLM3914todriveandregulateLEDspoweredfromapulsatingDCpowersource,i.e.,largelyunfiltered.(Duetopossibleoscillationsatlowvoltagesanominalbypassca-pacitorconsistingofa2.2µFsolidtantalumconnectedfromthepulsatingLEDsupplytopin2oftheLM3914isrecom-mended.)Thisabilitytooperatewithloworfluctuatingvolt-agesalsoallowsthedisplaydrivertointerfacewithlogiccir-cuitry,opto-coupledsolid-staterelays,andlow-currentincandescentlamps.
CascadingLM3914sinDotMode
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LM3914TypicalApplications
Zero-CenterMeter,20-Segment
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LM3914TypicalApplications
(Continued)
ExpandedScaleMeter,DotorBar
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*ThisapplicationillustratesthattheLEDsupplyneedspracticallynofiltering
Calibration:Withaprecisionmeterbetweenpins4and6adjustR1forvoltageVDof1.20V.Apply4.94Vtopin5,andadjustR4untilLEDNo.5justlights.Theadjustmentsarenon-interacting.
ApplicationExample:Grading5VRegulatorsHighestNo.LEDon
10987654321
ColorRedRedYellowGreenGreen5VGreenGreenYellowRedRed
4.944.824.74.584.46VOUT(MIN)5.545.425.305.185.06
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LM3914TypicalApplications
(Continued)
“ExclamationPoint”Display
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LEDslightupasillustratedwiththeupperlitLEDindicatingtheactualinputvoltage.Thedisplayappearstoincreaseresolutionandprovidesananalogindicationofoverrange.
IndicatorandAlarm,Full-ScaleChangesDisplayfromDottoBar
DS007970-10
*TheinputtotheDot-BarSwitchmaybetakenfromcathodesofotherLEDs.DisplaywillchangetobarassoonastheLEDsoselectedbeginstolight.
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LM3914TypicalApplications
(Continued)
BarDisplaywithAlarmFlasher
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Full-scalecausesthefullbardisplaytoflash.IfthejunctionofR1andC1isconnectedtoadifferentLEDcathode,thedisplaywillflashwhenthatLEDlights,andatanyhigherinputsignal.
AddingHysteresis(SingleSupply,BarModeOnly)
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Hysteresisis0.5mVto1mV
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LM3914TypicalApplications
(Continued)
OperatingwithaHighVoltageSupply(DotModeOnly)
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TheLEDcurrentsareapproximately10mA,andtheLM3914outputsoperateinsaturationforminimumdissipation.
*Thispointispartiallyregulatedanddecreasesinvoltagewithtemperature.VoltagerequirementsoftheLM3914alsodecreasewithtemperature.
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LM3914TypicalApplications
(Continued)
20-SegmentMeterwithModeSwitch
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*TheexactwiringarrangementofthisschematicshowstheneedforModeSelect(pin9)tosensetheProgramsLEDsto10mA
V+
voltageexactlyasitappearsonpin3.
ApplicationHints
ThreeofthemostcommonlyneededprecautionsforusingtheLM3914areshowninthefirsttypicalapplicationdrawingshowinga0V–5Vbargraphmeter.Themostdifficultprob-lemoccurswhenlargeLEDcurrentsarebeingdrawn,espe-ciallyinbargraphmode.Thesecurrentsflowingoutofthegroundpincausevoltagedropsinexternalwiring,andthuserrorsandoscillations.Bringingthereturnwiresfromsignalsources,referencegroundandbottomoftheresistorstring(asillustrated)toasinglepointverynearpin2isthebestso-lution.
LongwiresfromVLEDtoLEDanodecommoncancauseos-cillations.Dependingontheseverityoftheproblem0.05µFto2.2µFdecouplingcapacitorsfromLEDanodecommontopin2willdampthecircuit.IfLEDanodelinewiringisinac-cessible,oftensimilardecouplingfrompin1topin2willbesufficient.
IfLEDturnONseemsslow(barmode)orseveralLEDslight(dotmode),oscillationorexcessivenoiseisusuallytheprob-lem.Incaseswhereproperwiringandbypassingfailtostoposcillations,V+voltageatpin3isusuallybelowsuggestedlimits.Expandedscalemeterapplicationsmayhaveoneorbothendsoftheinternalvoltagedividerterminatedatrela-
tivelyhighvalueresistors.Thesehigh-impedanceendsshouldbebypassedtopin2withatleasta0.001µFcapaci-tor,orupto0.1µFinnoisyenvironments.
Powerdissipation,especiallyinbarmodeshouldbegivenconsideration.Forexample,witha5VsupplyandallLEDsprogrammedto20mAthedriverwilldissipateover600mW.Inthiscasea7.5ΩresistorinserieswiththeLEDsupplywillcutdeviceheatinginhalf.Thenegativeendoftheresistorshouldbebypassedwitha2.2µFsolidtantalumcapacitortopin2oftheLM3914.
TurningOFFofmostoftheinternalcurrentsourcesisac-complishedbypullingpositiveonthereferencewithacur-rentsourceorresistancesupplying100µAorso.Alternately,theinputsignalcanbegatedOFFwithatransistorswitch.Otherspecialfeaturesandapplicationscharacteristicswillbeillustratedinthefollowingapplicationsschematics.Noteshavebeenaddedinmanycases,attemptingtocoveranyspecialproceduresorunusualcharacteristicsoftheseappli-cations.Aspecialsectioncalled“ApplicationTipsfortheLM3914AdjustableReference”hasbeenincludedwiththeseschematics.
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LM3914ApplicationHints
(Continued)
GreatlyExpandedScale(BarModeOnly)
APPLICATIONTIPSFORTHELM3914ADJUSTABLEREFERENCE
GREATLYEXPANDEDSCALE(BARMODEONLY)
PlacingtheLM3914internalresistordividerinparallelwithasection(≅230Ω)ofastable,lowresistancedividergreatlyreducesvoltagechangesduetoICresistorvaluechangeswithtemperature.VoltageV1shouldbetrimmedto1.1VfirstbyuseofR2.ThenthevoltageV2acrosstheICdividerstringcanbeadjustedto200mV,usingR5withoutaffectingV1.LEDcurrentwillbeapproximately10mA.
NON-INTERACTINGADJUSTMENTSFOREXPANDEDSCALEMETER(4.5Vto5V,BarorDotMode)
ThisarrangementallowsindependentadjustmentofLEDbrightnessregardlessofmeterspanandzeroadjustments.First,V1isadjustedto5V,usingR2.Thenthespan(voltageacrossR4)canbeadjustedtoexactly0.5VusingR6withoutaffectingthepreviousadjustment.
R9programsLEDcurrentswithinarangeof2.2mAto20mAaftertheabovesettingsaremade.
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ADJUSTINGLINEARITYOFSEVERALSTACKEDDIVIDERS
Threeinternalvoltagedividersareshownconnectedinse-riestoprovidea30-stepdisplay.Iftheresultinganalogmeteristobeaccurateandlinearthevoltageoneachdividermustbeadjusted,preferablywithoutaffectinganyotheradjust-ments.Todothis,adjustR2first,sothatthevoltageacrossR5isexactly1V.ThenthevoltagesacrossR3andR4canbeindependentlyadjustedbyshuntingeachwithselectedresistorsof6kΩorhigherresistance.Thisispossiblebe-causethereferenceofLM3914No.3isactingasaconstantcurrentsource.
ThereferencesassociatedwithLM3914sNo.1andNo.2shouldhavetheirRefAdjpins(pin8)wiredtoground,andtheirRefOutputsloadedbya620Ωresistortoground.Thismakesavailablesimilar20mAcurrentoutputstoalltheLEDsinthesystem.
IfanindependentLEDbrightnesscontrolisdesired(asinthepreviousapplication),aunitygainbuffer,suchastheLM310,shouldbeplacedbetweenpin7andR1,similartothepreviousapplication.
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LM3914ApplicationHints
(Continued)
Non-InteractingAdjustmentsforExpandedScaleMeter(4.5Vto5V,BarorDotMode)
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AdjustingLinearityofSeveralStackedDividers
OtherApplications
••••••••
“Slow”—fadebarordotdisplay(doublesresolution)20-stepmeterwithsinglepotbrightnesscontrol10-step(ormultiples)programmerMulti-stepor“staging”controller
CombinedcontrollerandprocessdeviationmeterDirectionandrateindicator(toaddtoDVMs)Exclamationpointdisplayforpowersaving
Graduationscanbeaddedtodotdisplays.Dimlylightev-eryotherLEDusingaresistortoground
•Electronic“meter-relay”—displaycouldbecircleorsemi-circle
•Moving“hole”display—indicatorLEDisdark,restofbarlit
•Drivesvacuum-fluorescentandLCDsusingaddedpas-siveparts
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LM3914ConnectionDiagrams
PlasticChipCarrierPackage
Dual-in-LinePackage
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TopView
OrderNumberLM3914VSeeNSPackageNumberV20A
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TopView
OrderNumberLM3914N-1SeeNSPackageNumberNA18A
OrderNumberLM3914N*SeeNSPackageNumberN18A
*Discontinued,LifeTimeBuydate12/20/99
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LM3914PhysicalDimensions
inches(millimeters)unlessotherwisenoted
Note:Unlessotherwisespecified.1.StandardLeadFinish:
200microinches/5.08micrometerminimum
lead/tin37/63or15/85onalloy42orequivalentorcopper
2.ReferenceJEDECregistrationMS-001,VariationAC,datedMay1993.
Dual-In-LinePackage(N)OrderNumberLM3914N-1NSPackageNumberNA18A
PlasticChipCarrierPackage(V)
OrderNumberLM3914VNSPackageNumberV20A
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LM3914Dot/BarDisplayDriverPhysicalDimensions
inches(millimeters)unlessotherwisenoted(Continued)
Dual-In-LinePackage(N)OrderNumberLM3914N*NSPackageNumberN18A
*Discontinued,LifeTimeBuydate12/20/99
LIFESUPPORTPOLICY
NATIONAL’SPRODUCTSARENOTAUTHORIZEDFORUSEASCRITICALCOMPONENTSINLIFESUPPORTDEVICESORSYSTEMSWITHOUTTHEEXPRESSWRITTENAPPROVALOFTHEPRESIDENTANDGENERALCOUNSELOFNATIONALSEMICONDUCTORCORPORATION.Asusedherein:1.Lifesupportdevicesorsystemsaredevicesorsystemswhich,(a)areintendedforsurgicalimplantintothebody,or(b)supportorsustainlife,andwhosefailuretoperformwhenproperlyusedinaccordancewithinstructionsforuseprovidedinthelabeling,canbereasonablyexpectedtoresultinasignificantinjurytotheuser.
NationalSemiconductorCorporationAmericas
Tel:1-800-272-9959Fax:1-800-737-7018Email:support@nsc.com
www.national.com
NationalSemiconductorEurope
Fax:+49(0)180-5308586Email:europe.support@nsc.com
DeutschTel:+49(0)180-5308585EnglishTel:+49(0)180-5327832FrançaisTel:+49(0)180-5329358ItalianoTel:+49(0)180-5341680
2.Acriticalcomponentisanycomponentofalifesupportdeviceorsystemwhosefailuretoperformcanbereasonablyexpectedtocausethefailureofthelifesupportdeviceorsystem,ortoaffectitssafetyoreffectiveness.
NationalSemiconductorAsiaPacificCustomerResponseGroupTel:65-2544466Fax:65-2504466
Email:sea.support@nsc.com
NationalSemiconductorJapanLtd.
Tel:81-3-5639-7560Fax:81-3-5639-7507
Nationaldoesnotassumeanyresponsibilityforuseofanycircuitrydescribed,nocircuitpatentlicensesareimpliedandNationalreservestherightatanytimewithoutnoticetochangesaidcircuitryandspecifications.
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