[LM334恒流芯片] 7136恒流芯片详解
LM134/LM234/LM3343-TerminalAdjustableCurrentSources
March2000
LM134/LM234/LM334
3-TerminalAdjustableCurrentSources
GeneralDescription
The
LM134/LM234/LM334are3-terminaladjustablecurrentsourcesfeaturing10,000:1rangeinoperatingcurrent,excel-lentcurrentregulationandawidedynamicvoltagerangeof1Vto40V.Currentisestablishedwithoneexternalresistorandnootherpartsarerequired.Initialcurrentaccuracyis±3%.TheLM134/LM234/LM334aretruefloatingcurrentsourceswithnoseparatepowersupplyconnections.Inaddi-tion,reverseappliedvoltagesofupto20Vwilldrawonlyafewdozenmicroamperesofcurrent,allowingthedevicestoactasbotharectifierandcurrentsourceinACapplications.ThesensevoltageusedtoestablishoperatingcurrentintheLM134is64mVat25˚Candisdirectlyproportionaltoabso-lutetemperature(˚K).Thesimplestoneexternalresistorconnection,then,generatesacurrentwith≈+0.33%/˚Ctem-peraturedependence.Zerodriftoperationcanbeobtainedbyaddingoneextraresistorandadiode.
Applicationsforthecurrentsourcesincludebiasnetworks,surgeprotection,lowpowerreference,rampgeneration,
LEDdriver,andtemperaturesensing.TheLM234-3andLM234-6arespecifiedastruetemperaturesensorswithguaranteedinitialaccuracyof±3˚Cand±6˚C,respectively.Thesedevicesareidealinremotesenseapplicationsbe-causeseriesresistanceinlongwirerunsdoesnotaffectac-curacy.Inaddition,only2wiresarerequired.
TheLM134isguaranteedoveratemperaturerangeof−55˚Cto+125˚C,theLM234from−25˚Cto+100˚CandtheLM334from0˚Cto+70˚C.ThesedevicesareavailableinTO-46hermetic,TO-92andSO-8plasticpackages.
Features
nnnnnn
Operatesfrom1Vto40V0.02%/Vcurrentregulation
Programmablefrom1µAto10mATrue2-terminaloperation
Availableasfullyspecifiedtemperaturesensor±3%initialaccuracy
ConnectionDiagrams
SO-8
SurfaceMountPackage
SO-8AlternativePinoutSurfaceMountPackage
TO-46
MetalCanPackage
DS005697-24
DS005697-12
DS005697-25
OrderNumberLM334Mor
LM334MX
SeeNSPackageNumberM08A
OrderNumberLM334SMor
LM334SMX
SeeNSPackageNumberM08A
VPiniselectricallyconnectedtocase.
−
BottomView
OrderNumberLM134H,LM234HorLM334HSeeNSPackageNumberH03H
TO-92PlasticPackage
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BottomView
OrderNumberLM334Z,LM234Z-3orLM234Z-6
SeeNSPackageNumberZ03A
2000NationalSemiconductorCorporationDS005697
LM134/LM234/LM334
AbsoluteMaximumRatings
(Note1)
IfMilitary/Aerospacespecifieddevicesarerequired,pleasecontacttheNationalSemiconductorSalesOffice/Distributorsforavailabilityandspecifications.V+toV−ForwardVoltageLM134/LM234/LM334LM234-3/LM234-6+
VtoV−ReverseVoltageRPintoV−VoltageSetCurrent
PowerDissipation
ESDSusceptibility(Note6)
OperatingTemperatureRange(Note5)LM134
40V30V20V5V10mA400mW2000V
−55˚Cto+125˚C
LM234/LM234-3/LM234-6−25˚Cto+100˚CLM3340˚Cto+70˚CSolderingInformation
TO-92Package(10sec.)260˚CTO-46Package(10sec.)300˚CSOPackage
VaporPhase(60sec.)215˚CInfrared(15sec.)220˚CSeeAN-450“SurfaceMountingMethodsandTheirEffectonProductReliability”(AppendixD)forothermethodsofsol-deringsurfacemountdevices.
ElectricalCharacteristics(Note2)
Parameter
SetCurrentError,V+=2.5V,(Note3)
RatioofSetCurrenttoBiasCurrent
MinimumOperatingVoltage
Conditions
Min
10µA≤ISET≤1mA1mA
1mA
AverageChangeinSetCurrentwithInputVoltage
2µA≤ISET≤1mA1.5≤V+≤5V5V≤V≤40V1mA
TemperatureDependenceofSetCurrent(Note4)EffectiveShuntCapacitance
15
15
pF
Note1:.“AbsoluteMaximumRatings”indicatelimitsbeyondwhichdamagetothedevicemayoccur.OperatingRatingsindicateconditionsforwhichthedeviceisfunctional,butdonotguaranteespecificperformancelimits.
Note2:Unlessotherwisespecified,testsareperformedatTj=25˚Cwithpulsetestingsothatjunctiontemperaturedoesnotchangeduringtest
Note3:SetcurrentisthecurrentflowingintotheV+pin.FortheBasic2-TerminalCurrentSourcecircuitshownonthefirstpageofthisdatasheet.ISETisdeterminedbythefollowingformula:ISET=67.7mV/RSET(@25˚C).Setcurrenterrorisexpressedasapercentdeviationfromthisamount.ISETincreasesat0.336%/˚C@Tj=25˚C(227µV/˚C).
Note4:ISETisdirectlyproportionaltoabsolutetemperature(˚K).ISETatanytemperaturecanbecalculatedfrom:ISET=Io(T/To)whereIoisISETmeasuredatTo(˚K).
Note5:Forelevatedtemperatureoperation,TJmaxis:
+
LM134/LM234
Typ
Max358
14
1814180.80.91.00.020.010.030.02
0.96T
T
1.04T
0.96T
0.050.032323
14Min
LM334Typ
Max6812
1814180.80.91.00.020.010.030.02T
1.04T0.10.052626
Units%%%
VVV%/V%/V%/V%/V
25µA≤ISET≤1mA
LM134LM234LM334
ThermalResistanceθja(JunctiontoAmbient)θjc(JunctiontoCase)
150˚C125˚C100˚C
TO-92
180˚C/W(0.4"leads)160˚C/W(0.125"leads)
N/A
32˚C/W
80˚C/W
TO-46440˚C/W
SO-8165˚C/W
Note6:Humanbodymodel,100pFdischargedthrougha1.5kΩresistor.
2
LM134/LM234/LM334
ElectricalCharacteristics(Note
2)
Parameter
SetCurrentError,V+=2.5V,(Note3)
EquivalentTemperatureErrorRatioofSetCurrenttoBiasCurrent
MinimumOperatingVoltageAverageChangeinSetCurrentwithInputVoltage
TemperatureDependenceofSetCurrent(Note4)andEquivalentSlopeErrorEffectiveShuntCapacitance
15
100µAISET≤1mA100µA≤ISET≤1mA
1.5≤V+≤5V5V≤V+≤30V100µA≤ISET≤1mA
0.98T
0.020.01T
0.050.031.02T
0.97T
0.020.01T
0.010.051.03T
%/V%/V
0.9
0.9
V
100µA≤ISET≤1mA
14
18
Conditions
Min
100µA≤ISET≤1mATJ=25˚
LM234-3Typ
Max
Min
LM234-6Typ
Max
Units
±1±2
%
±3
26
14
18
±6
26
˚C
±2
15
±3
%pF
3
LM134/LM234/LM334
TypicalPerformanceCharacteristics
OutputImpedance
MaximumSlewRateLinearOperation
DS005697-30
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Start-UpTransientResponse
DS005697-32
DS005697-33
VoltageAcrossRSET(VR)CurrentNoise
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DS005697-35
4
LM134/LM234/LM334
TypicalPerformanceCharacteristics
Turn-OnVoltage
(Continued)
RatioofISETtoIBIAS
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ApplicationHints
TheLM134hasbeendesignedforeaseofapplication,butageneraldiscussionofdesignfeaturesispresentedheretofamiliarizethedesignerwithdevicecharacteristicswhichmaynotbeimmediatelyobvious.Theseincludetheeffectsofslewing,powerdissipation,capacitance,noise,andcon-tactresistance.CALCULATINGRSET
ThetotalcurrentthroughtheLM134(ISET)isthesumofthecurrentgoingthroughtheSETresistor(IR)andtheLM134’sbiascurrent(IBIAS),asshowninFigure1.
wherenistheratioofISETtoIBIASasspecifiedintheElec-tricalCharacteristicsSectionandshowninthegraph.Sincenistypically18for2µA≤ISET≤1mA,theequationcanbefurthersimplifiedto
formostsetcurrents.
SLEWRATE
Atslewratesaboveagiventhreshold(seecurve),theLM134mayexhibitnon-linearcurrentshifts.TheslewingrateatwhichthisoccursisdirectlyproportionaltoISET.AtISET=10µA,maximumdV/dtis0.01V/µs;atISET=1mA,thelimitis1V/µs.SlewratesabovethelimitdonotharmtheLM134,orcauselargecurrentstoflow.
THERMALEFFECTS
Internalheatingcanhaveasignificanteffectoncurrentregu-lationforISETgreaterthan100µA.Forexample,each1Vin-creaseacrosstheLM134atISET=1mAwillincreasejunc-tiontemperatureby≈0.4˚Cinstillair.Outputcurrent(ISET)hasatemperaturecoefficientof≈0.33%/˚C,sothechangeincurrentduetotemperaturerisewillbe(0.4)(0.33)=0.132%.Thisisa10:1degradationinregulationcomparedtotrueelectricaleffects.Thermaleffects,therefore,mustbetakenintoaccountwhenDCregulationiscriticalandISETexceeds100µA.HeatsinkingoftheTO-46packageortheTO-92leadscanreducethiseffectbymorethan3:1.
SHUNTCAPACITANCE
Incertainapplications,the15pFshuntcapacitanceoftheLM134mayhavetobereduced,eitherbecauseofloadingproblemsorbecauseitlimitstheACoutputimpedanceofthecurrentsource.ThiscanbeeasilyaccomplishedbybufferingtheLM134withanFETasshownintheapplications.Thiscanreducecapacitancetolessthan3pFandimproveregu-lationbyatleastanorderofmagnitude.DCcharacteristics(withtheexceptionofminimuminputvoltage),arenotaf-fected.
DS005697-27
FIGURE1.BasicCurrentSource
AgraphshowingtheratioofthesetwocurrentsissuppliedunderRatioofISETtoIBIASintheTypicalPerformanceCharacteristicssection.ThecurrentflowingthroughRSETisdeterminedbyVR,whichisapproximately214µV/˚K(64mV/298˚K∼214µV/˚K).
Since(foragivensetcurrent)IBIASissimplyapercentageofISET,theequationcanberewritten
5
LM134/LM234/LM334
ApplicationHints
NOISE
(Continued)
APPLICATIONASAZEROTEMPERATURECOEFFICENTCURRENTSOURCE
AddingadiodeandaresistortothestandardLM134con-figurationcancancelthetemperature-dependentcharacter-isticoftheLM134.ThecircuitshowninFigure3balancesthepositivetempcooftheLM134(about+0.23mV/˚C)withthenegativetempcoofaforward-biasedsilicondiode(about−2.5mV/˚C).
CurrentnoisegeneratedbytheLM134isapproximately4timestheshotnoiseofatransistor.IftheLM134isusedasanactiveloadforatransistoramplifier,inputreferrednoisewillbeincreasedbyabout12dB.Inmanycases,thisisac-ceptableandasinglestageamplifiercanbebuiltwithavolt-agegainexceeding2000.LEADRESISTANCE
ThesensevoltagewhichdeterminesoperatingcurrentoftheLM134islessthan100mV.Atthislevel,thermocoupleorleadresistanceeffectsshouldbeminimizedbylocatingthecurrentsettingresistorphysicallyclosetothedevice.Sock-etsshouldbeavoidedifpossible.Ittakesonly0.7Ωcontactresistancetoreduceoutputcurrentby1%atthe1mAlevel.SENSINGTEMPERATURE
TheLM134makesanidealremotetemperaturesensorbe-causeitscurrentmodeoperationdoesnotloseaccuracyoverlongwireruns.OutputcurrentisdirectlyproportionaltoabsolutetemperatureindegreesKelvin,accordingtothefol-lowingformula:
CalipationoftheLM134isgreatlysimplifiedbecauseofthefactthatmostoftheinitialinaccuracyisduetoagainterm(slopeerror)andnotanoffset.Thismeansthatacalipationconsistingofagainadjustmentonlywilltrimbothslopeandzeroatthesametime.Inaddition,gainadjustmentisaonepointtrimbecausetheoutputoftheLM134extrapolatestozeroat0˚K,independentofRSEToranyinitialinaccuracy.
DS005697-28
FIGURE3.ZeroTempcoCurrentSource
Thesetcurrent(ISET)isthesumofI1andI2,eachcontribut-ingapproximately50%ofthesetcurrent,andIBIAS.IBIASisusuallyincludedintheI1termbyincreasingtheVRvalueusedforcalculationsby5.9%.(SeeCALCULATINGRSET.)
Thefirststepistominimizethetempcoofthecircuit,usingthefollowingequations.Anexampleisgivenusingavalueof+227µV/˚CasthetempcooftheLM134(whichincludestheIBIAScomponent),and−2.5mV/˚Casthetempcoofthedi-ode(forbestresults,thisvalueshouldbedirectlymeasuredorobtainedfromthemanufacturerofthediode).
DS005697-4
FIGURE2.GainAdjustment
ThispropertyoftheLM134isillustratedintheaccompanyinggraph.Lineabcisthesensorcurrentbeforetrimming.Linea"b"c"isthedesiredoutput.AgaintrimdoneatT2willmovetheoutputfrombtob"andwillsimultaneouslycorrecttheslopesothattheoutputatT1andT3willbecorrect.ThisgaintrimcanbedoneonRSETorontheloadresistorusedtoterminatetheLM134.Slopeerroraftertrimwillnormallybelessthan±1%.Tomaintainthisaccuracy,however,alowtemperaturecoefficientresistormustbeusedforRSET.A33ppm/˚CdriftofRSETwillgivea1%slopeerrorbecausetheresistorwillnormallyseeaboutthesametemperaturevariationsastheLM134.SeparatingRSETfromtheLM134requires3wiresandhasleadresistanceproblems,soisnotnormallyrecommended.Metalfilmresistorswithlessthan20ppm/˚Cdriftarereadilyavailable.Wirewoundresistorsmayalsobeusedwherebeststabilityisrequired.
6
WiththeR1toR2ratiodetermined,valuesforR1andR2shouldbedeterminedtogivethedesiredsetcurrent.TheformulaforcalculatingthesetcurrentatT=25˚Cisshownbelow,followedbyanexamplethatassumestheforwardvoltagedropacrossthediode(VD)is0.6V,thevoltageacrossR1is67.7mV(64mV+5.9%toaccountforIBIAS),andR2/R1=10(fromthepreviouscalculations).
LM134/LM234/LM334
ApplicationHints
(Continued)
Iftheestimateforthetempcoofthediode’sforwardvoltagedropwasoff,thetempcocancellationisstillreasonablyef-fective.Assumethetempcoofthediodeis2.6mV/˚Cinsteadof2.5mV/˚C(anerrorof4%).Thetempcoofthecircuitisnow:
ThiscircuitwilleliminatemostoftheLM134’stemperaturecoefficient,anditdoesagoodjobeveniftheestimatesofthediode’scharacteristicsarenotaccurate(asthefollowingex-amplewillshow).ForlowesttempcowithaspecificdiodeatthedesiredISET,however,thecircuitshouldbebuiltandtestedovertemperature.IfthemeasuredtempcoofISETispositive,R2shouldbereduced.Iftheresultingtempcoisnegative,R2shouldbeincreased.Therecommendeddiodeforuseinthiscircuitisthe1N457becauseitstempcoiscen-teredat11timesthetempcooftheLM134,allowingR2=10R1.Youcanalsousethiscircuittocreateacurrentsourcewithnon-zerotempcosbysettingthetempcocomponentofthetempcoequationtothedesiredvalueinsteadof0.EXAMPLE:A1mA,Zero-TempcoCurrentSourceFirst,solveforR1andR2:
A1mALM134currentsourcewithnotemperaturecompen-sationwouldhaveasetresistorof68Ωandaresultingtempcoof
Soevenifthediode’stempcovariesasmuchas±4%fromitsestimatedvalue,thecircuitstilleliminates98%oftheLM134’sinherenttempco.
TypicalApplications
GroundReferredFahrenheitThermometer
ThevaluesofR1andR2canbechangedtostandard1%re-sistorvalues(R1=133ΩandR2=1.33kΩ)withlessthana0.75%error.
Iftheforwardvoltagedropofthediodewas0.65Vinsteadoftheestimateof0.6V(anerrorof8%),theactualsetcurrentwillbe
DS005697-15
*SelectR3=VREF/583µA.VREFmaybeanystablepositivevoltage≥2V
TrimR3tocalipate
anerroroflessthan5%.
7
TypicalApplications
(Continued)
LowOutputImpedance
Thermometer
TerminatingRemoteSensorforVoltage
Output
DS005697-6
*OutputimpedanceoftheLM134atthe“R”pinis
approximately
DS005697-14
LM134/LM234/LM334
TypicalApplications
(Continued)
LowInputVoltageReferenceDriver
MicropowerBias
DS005697-17
DS005697-18
RampGenerator
DS005697-19
9
LM134/LM234/LM334
TypicalApplications
(Continued)
1.2VRegulatorwith1.8VMinimumInput
1.2VReferenceOperateson10µAand2V
DS005697-20
*SelectratioofR1toR2toobtainzerotemperaturedrift
DS005697-7
*SelectratioofR1toR2forzerotemperaturedrift
ZenerBiasingAlternateTrimmingTechniqueBufferforPhotoconductiveCell
DS005697-51
DS005697-49
DS005697-50
*For±10%adjustment,selectRSET10%high,andmakeR1≈3RSET
FETCascodingforLowCapacitanceand/orUltraHighOutputImpedance
DS005697-21
*SelectQ1orQ2toensureatleast1VacrosstheLM134.Vp(1−ISET/IDSS)≥1.2V.
DS005697-22
10
LM134/LM234/LM334
TypicalApplications
(Continued)
In-LineCurrentLimiter
GeneratingNegativeOutputImpedance
DS005697-23
*ZOUT≈−16•R1(R1/VINmustnotexceedISET)
DS005697-9
*Useminimumvaluerequiredtoensurestabilityofprotecteddevice.Thisminimizesinrushcurrenttoadirectshort.
SchematicDiagram
DS005697-11
11
LM134/LM234/LM334
PhysicalDimensions
inches
(millimeters)unlessotherwisenoted
OrderNumberLM134H,LM234HorLM334H
NSPackageNumberH03H
12
LM134/LM234/LM334
PhysicalDimensions
inches
(millimeters)unlessotherwisenoted(Continued)
SOPackage(M)
OrderNumberLM334M,LM334MX,
LM334SMorLM334SMXNSPackageNumberM08A
OrderNumberLM334Z,LM234Z-3orLM234Z-6
NSPackageNumberZ03A
13
LM134/LM234/LM3343-TerminalAdjustableCurrentSources
Notes
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