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2024-07-28 作者:

LM3915

LM3915 Dot/Bar Display Driver

Literature Number: SNVS740B

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LM3915

Dot/BarDisplayDriver

GeneralDescription

TheLM3915isamonolithicintegratedcircuitthatsensesanalogvoltagelevelsanddrivestenLEDs,LCDsorvacuumfluorescentdisplays,providingalogarithmic3dB/rentdriveisregulatedandprogrammable,ledisplaysystemcanoperatefromasinglesupplyaslowas3Vorashighas25V.

TheICcontainsr,itneedsnoprotectionagainstinputsof±utbuffcyistypicallybetterthan1dB.

TheLM3915’s3dB/stepdisplayissuitedforsignalswithwidedynamicrange,suchasaudiolevel,power,pplicationsincludeaverageorpeaklevelindicators,ingconventionalmeterswithanLEDbargraphresultsinafasterresponding,moreruggeddisplaywithhighvisibilitythatretainstheeaseofinterpretationofananalogdisplay.

ghtnessiseasilycontrolledwithasinglepot.

putscandriveLCDs,le3915scanalsobecascadedwithLM3914sforalinear/logdisplayorwithLM3916sforanextended-rangeVUmeter.

Features

3dB/step,30dBrange

DrivesLEDs,LCDs,orvacuumfluorescents

BarordotdisplaymodeexternallyselectablebyuserExpandabletodisplaysof90dB

Internalvoltagereferencefrom1.2Vto12VOperateswithsinglesupplyof3Vto25VInputsoperatedowntoground

Outputcurrentprogrammablefrom1mAto30mA

Inputwithstands±35VwithoutdamageorfalseoutputsOutputsarecurrentregulated,opencollectorsDirectlydrivesTTLorCMOS

Theinternal10-stepdividerisfloatingandcanbereferencedtoawiderangeofvoltages

TheLM3915isratedforoperationfrom0˚Cto+70˚nnnnnn

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0Vto10VLogDisplay

00510

Notes:CapacitorC1isrequiredifleadstotheLEDsupplyare6"orlonger.

mode,stbekeptbelow7VordroppingresistorshouldbeusedtolimitIdissipation.

2

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pleasecontacttheNationalSemiconductorSalesOffice/issipation(Note6)

MoldedDIP(N)SupplyVoltage

VoltageonOutputDrivers

1365mW

25V25V

ReferenceLoadCurrentStorageTemperatureRangeLeadTemperature(Soldering,10sec.)

10mA

−55˚Cto+150˚C

260˚C

ElectricalCharacteristics(Notes2,4)

Parameter

COMPARATOR

OffsetVoltage,BufferandFirstComparator

OffsetVoltage,BufferandAnyOtherComparatorGain(∆ILED/∆VIN)

InputBiasCurrent(atPin5)InputSignalOvervoltageVOLTAGE-DIVIDERDividerResistance

RelativeAccuracy(InputChangeBetweenAnyTwoThresholdPoints)

AbsoluteAccuracyatEachThresholdPoint

Total,Pin6to4(Note3)(Note3)VIN=−3,−6dBVIN=−9dB

VIN=−12,−15,−18dBVIH=−21,−24,−27dB

VOLTAGEREFERENCEOutputVoltageLineRegulationLoadRegulation

OutputVoltageChangewithTemperatureAdjustPinCurrentOUTPUTDRIVERSLEDCurrent

LEDCurrentDifference(BetweenLargestandSmallestLEDCurrents)LEDCurrentRegulationDropoutVoltageSaturationVoltage

OutputLeakage,EachCollectorOutputLeakagePins10–18Pin1

V

+Conditions(Note2)

0V≤VRLO=VRHI≤12V,ILED=1mA

0V≤VRLO=VRHI≤12V,ILED=1mA

IL(REF)=2mA,ILED=10mA0V≤VIN≤(V+−1.5V)NoChangeinDisplay

MinTypMaxUnits

33

3−35162.0

283.0825

1015

mVmVmA/mV

10035364.0

nAVkΩdB

−0.5−0.5−0.5−0.5

+0.5+0.65+1.0+1.5

dBdBdBdB

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+=VLED=5V

1.21.280.010.4175

1.340.032

V%/V%%

120130.430.2531.5

µAmAmAmAVVµAµAµA

=VLED=5V,IL(REF)=1mA

7100.121.20.11

VLED=5V,ILED=2mAVLED=5V,ILED20mA2V≤VLED≤17V,ILED=2mAILED=20mA

ILED(ON)=20mA,@VLED=5V,∆ILED=2mA

ILED=2.0mA,IL(REF)=0.4mA(BarMode)(Note5)(DotMode)(Note5)

0.150.10.1

60

150

0.41010450

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SUPPLYCURRENTStandbySupplyCurrent(AllOutputsOff)

V+=+5V,IL(REF)=0.2mAV+=+20V,IL(REF)=1.0mA

2.46.1

4.29.2

Note1:AbsoluteMingRatingsindicateconditionsforwhichthefunctional,icalCharacteristicsstateDCandACelectricalspecificatioicationsarenotguaranteedforparameterswhereisgiven,however,2:Unlessotherwisestated,allspecificationsapplywiththefollowingconditions:3VDC≤V+≤20VDC3VDC≤VLED≤

V+

−0.015V≤VRHI≤12VDC

−0.015V≤VRLO≤12VDCVREF,VRHI,VRLO≤

0V≤VIN≤

(V+

−1.5V)V+

−1.5V

TA=25˚C,IL(REF)=0.2mA,pin9connectedtopin3(barmode).Forhigherpowerdissipations,pulsetestingisused.

Note3:Accuracyismeasuredreferredto0dB=+10.000VDCatpin5,with+10.000VDCatpin6,rfullscalevoltages,leforthresholdvoltages.

Note4:Pin5inputcurrentmustbelimitedto±itionofa39kresistorinserieswithpin5allows±100Vsignalswithoutdamage.

Note5:Barmoderesultswhenpin9iswithin20mVofV+.Dotmoderesultswhenpin9ispulledatleast200mVbelowV+.LED#10(pin10outputcudisabledifpin9ispulled0.9VormorebelowVLED.

Note6:ThemaximumjunctiontemperatureoftheLM3915is100˚ontoambienresistanceis55˚C/WforthemoldedDIP(Npackage).

ThresholdVoltage(Note3)

Output

12345

dB−27−24−21−18−15

Min0.4220.5960.8411.1891.679

Typ0.4470.6310.8911.2591.778

Max0.5310.7501.0591.4131.995

Output

678910

dB−12−9−6−30

Min2.3723.3504.7326.6839.985

Typ2.5123.5485.0127.07910

2

3

5

7

1

4

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SupplyCurrentvsTemperatureOperatingInputBiasCurrentvsTemperature

10435

ReferenceVoltagevs

TemperatureReferenceAdjustPinCurrentvsTemperature

00510436

00510437

LEDCurrent-Regulation

DropoutLEDDriverSaturation

Voltage

00510438

00510439

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InputCurrentBeyondSignalRange(Pin5)LEDCurrentvsReferenceLoading

00510440

00510441

LEDDriverCurrent

RegulationTotalDividerResistance

vsTemperature

00510442

00510443

Common-ModeLimitsOutputCharacteristics

00510444

00510445

6

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00510404

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generalideaofthecircuit’nputimped-ancebufferoperateswithsignalsfromgroundto12V,-nalisthenappliedtoaseriesof10comparators;eachofwhichisbiasedtoadifferentcomparisonlevelbytheresistorstring.

Intheexampleillustrated,case,foreach3dBthattheinputsignalincreases,sistordividercanbecon-nectedbetweenany2voltages,providingthattheyareatleast1.5VbelowV+andnolowerthanV−.INTERNALVOLTAGEREFERENCE

Thereferenceisdesignedtobeadjustableanddevelopsanominal1.25VbetweentheREFOUT(pin7)andREFADJ(pin8)erencevoltageisimpressedacrossprogramresistorR1and,sincethevoltageisconstant,aconstantcurrentI1thenflowsthroughtheoutputsetresistorR2givinganoutputvoltageof:

00510406

Outputsmayberuectiverationresistanceoftheoutputtransistors,equaltoRthetransistors’collectorresistance,isabout50Ω.ItpossibletodriveLEDsfromrectifiedACwithnofilteravoidoscillations,theLEDsupplyshouldbebypassed2.2µFtantalumor10µFaluminumelectrolyticcapac

00510405

MODEPINUSE

Pin9,theModeSelectinput,permitschainingofmLM3915s,andcontrolsbarordotmodeoperationfollowingtabulationshowsthebasicwaysofusingthisOthermorecomplexuseswillbeillustratedintheations.

BarGraphDisplay:WireModeSelect(pin9)directly3(V+pin).

DotDisplay,SingleLM3915Driver:LeavetheModepinopencircuit.

DotDisplay,20orMoreLEDs:,theonewiththelowestinputvcomparisonpoints)topin1ofthenexthigherLM3915Continueconnectingpin3915driverinthechainwillhavepin9leftoppreviousdriversshouldhavea20kresistorinparallLED#9(pin11toVLED).

Sincethe120µAcurrent(max)fromtheadjustterminalrepresentsanerrorterm,thereferencewasdesignedtominimizechangesofthiscurrentwithV+rectoperation,referenceloadcurrentshouldbebe-tween80µpacitanceshouldbelessthan0.05µF.

CURRENTPROGRAMMING

Afeaturenotrentdrawnoutofthereferencevoltagepin(pin7)-proximately10timesthiscurrentwillbedrawnthrougheachlightedLED,andthiscurrentwiltdrawnbytheinternal10-resistordivider,aswellasbytheexternalcurrentandvoltlitytomodu-lateLEDbrightnesswithtime,orinproportiontoinputvolt-ageandothersignalscanleadtoanumberofnoveldisplaysorwaysofindicatinginputovervoltages,alarms,etc.

currentisheldatabout10timesthereferenceloadcurrent,independentofoutputvoltageandprocessingvariables,aslongasthetransistorisnotsatu-rated.

8

ModePinFunctionalDescriptio

othefiedblockdiagrambelow.

BlockDiagramofModePinFunction

00510

*Highforbar

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DOTORBARMODESELECTION

Thevoltageatpin9issensedbycomparatorC1,nominallyreferencedto(V+−100mV).Thechipisinbarmodewhenpin9isabovethislevel;otherwiseit’paratorisdesignedsothatpin9canbeleftopencircuitfordotmode.

Takingintoaccountcomparatorgainandvariationinthe100mVreferencelevel,pin9shouldbenomorethan20mVbelowV+forbarmodeandmorethan200mVbelowV+(oropencircuit)applications,pin9iseitheropen(dotmode)ortiedtoV+(barmode).Inbarmode,urrentsdrawnfromthepowersupply(LEDcurrent,forexample)ECARRY

InorderforthedisplaytomakesensewhenmultipleLM3915sarecascadedindotmode,specialcircuitryhasbeenincludedtoshutoffLED#10ofthefirstdevicewhenLED#nectionforcascadingindotmodehasalreadybeendescribedandisdepictedbelow.

AslongastheinputsignalvoltageisbelowthethresholdofthesecondLM3915,LED#9ofLM3915#astheinputvoltagereachesthethresholdofLED#11,pin9ofLM3915#1ispulledanLEDdrop(1.5Vormore)nditionissensedbycomparatorC2,rcestheoutputofC2low,whichshutsoffoutputtransistorQ2,extinguishingLED#10.

ysmallcurrent(lessthan100µA)thatisdivertedfromLED#9doesnotnoticeablyaffectitsintensity.

Anauxiliarycurrentsourceatpin1keepsatleast100µAflowingthroughLED#suresthatpin9ofLM3915#1isheldlowenoughtoforceLED#100µAdoesnotnor-mallyproducesignificantLEDillumination,iisbothersome,thesimplecureistoshuntLED#1VIRdropismorethanthe900mV

OTHERDEVICECHARACTERISTICS

TheLM3915isrelativelylow-powereditself,andsinceanynumberofLEDscanbepoweredfromabout3V,lstandbysupplycurrent(allLEDsOFF)r,anyreferenceloadingadds4timesthatcurrentdraintotheV+(pin3)mple,anLM3916witha1mAreferencepinload(1.3k)wouldsupplyalmost10mAtoeveryLEDwhiledrawingonly10mAfromitsV+-scale,theICistypicallydrawinglessthan10%playdriverdoesnothavebuilt-inhyapidlychangingsignalconditions,“over-lap”ngemaybemuchmorerapidbetweenLED#10ofonedeviceandLED#1ofaseconddevice“chained”tothefirst.

ApplicationHints

ThemostdifficultproblemoccurswhenlargeLEDcurrentsarebeingdrawn,ur-rentsflowingoutofthegroundpincausevoltagedropsinexternalwiring,ngthereturnwiresfromsignalsources,referencegroundandbot-tomoftheresistorstringtoasinglepointverynearpin2isthebestsolution.

ingontheseverityoftheproblem0.05µFto2.2µnodelinewiringisinaccessible,oftensimilardecouplingfrompin1topin2willbesufficient.

IfLEDturnONseemsslow(barmode)orseveralLEDslight(dotmode),swhereproperwiringandbypassingfailtostoposcillations,V+edscalemeterapplicationsmayhaveoneorbothendsofthigh-impedanceendsshouldbebypassedtopin2withatleasta0.001µFcapaci-tor,orupto0.1µFinnoisyenvironments.

CascadingLM3915sinDotMode

00510408

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分销商库存信息:

NATIONAL-SEMICONDUCTORLM3915N-1/NOPB

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