LM2687MM资料

LM2687LowNoiseRegulatedSwitchedCapacitorVoltageInverterApril2003

LM2687

LowNoiseRegulatedSwitchedCapacitorVoltageInverter

GeneralDescription

TheLM2687CMOSNegativeRegulatedSwitchedCapacitorVoltageInverterdeliversaverylownoiseadjustableoutputforaninputvoltageintherangeof+2.7Vto+5.5V.Fourlowcostcapacitorsareusedinthiscircuittoprovideupto10mAofoutputcurrent.TheregulatedoutputfortheLM2687isadjustablebetween−1.5Vand−5.2V.TheLM2687operatesat100kHz(typical)switchingfrequencytoreduceoutputresistanceandvoltageripple.Withanoperatingcurrentofonly500µA(chargepumppowerefficiencygreaterthan90%withmostloads)and0.05µAtypicalshutdowncurrent,theLM2687providesidealperformanceforcellularphonepoweramplifierbiasandotherlowcurrent,lownoisenega-tivevoltageneeds.Thedevicecomesinasmall8-pinMSOPorLLPpackage.

Features

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InvertsandregulatestheinputsupplyvoltageSmallMSOP-8orLLP-8package

91%typicalchargepumppowerefficiencyat10mALowoutputripple(1mVtypical)

ShutdownlowersQuiescentcurrentto0.05µA(typical)

Applications

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WirelessCommunicationSystems

CellularPhonePowerAmplifierBiasingInterfacePowerSuppliesHandheldInstrumentationLaptopComputersandPDA’s

TypicalApplicationCircuit

10118001

ConnectionDiagrams

8-PinMSOP

8-PinLLP

10118002

10118025

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LM2687OrderingInformationforMSOPPackage

DeviceOrderNumber

LM2687MMLM2687MMX

PackageNumber

MUA08AMUA08A

PackageMarking*

S12AS12A

SuppliesAs

TapeandReel(1000units/reel)TapeandReel(3500units/reel)

OrderingInformationforLLPPackage

DeviceOrderNumber

LM2687LDLM2687LDX

PackageNumber

LDA08ALDA08A

PackageMarking*

L050BL050B

SuppliesAs

TapeandReel(1000units/reel)TapeandReel(3500units/reel)

Note:*ThesmallphysicalsizesoftheMSOP-8andLLP-8packagesdonot

allowforthefullpartnumbermarking.DeviceswillbemarkedwiththedesignationshowninthecolumnPackageMarking.

PinDescription

PinNo.12345678DAP

NameCap+GNDCap−SDVNEGVFBVOUTVINDieAttachPad

PositiveterminalforC1.Ground.

NegativeterminalforC1.

Activelow,logic-levelshutdowninput.Negativeunregulatedoutputvoltage.

Feedbackinput.ConnectVFBtoanexternalresistordividerbetweenVOUTandapositiveadjustvoltageVADJ(0≤VADJ≤VIN).DONOTleaveunconnected.Regulatednegativeoutputvoltage.Positivepowersupplyinput.

LLPpackageonly.ConnectthispadtoVNEG.

Function

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LM2687AbsoluteMaximumRatings

(Note1)

TJMAX(Note3)θJA(Note3)

OperatingInputVoltageRangeOperatingOutputCurrentRangeOperatingAmbientTemp.Range

OperatingJunctionTemp.RangeStorageTemperature

LeadTemp.(Soldering,10sec.)ESDRating(Note4)

150˚C250˚C/W2.7Vto5.5V0mAto10mA−40˚Cto85˚C−40˚Cto110˚C−65˚Cto150˚C

300˚C2kV

IfMilitary/Aerospacespecifieddevicesarerequired,pleasecontacttheNationalSemiconductorSalesOffice/Distributorsforavailabilityandspecifications.SupplyVoltage(VINtoGNDorGNDtoOUT)SD

VNEGandVOUTContinuousOutputCurrent

VOUTShort-CircuitDurationtoGND(Note2)

ContinuousPowerDissipation(TA=25˚C)(Note3)

+5.8V

(GND−0.3V)to

(VIN+0.3V)

10mA1sec.600mW

ElectricalCharacteristics

LimitswithstandardtypefaceapplyforTJ=25˚C,andlimitsinboldfacetypeapplyoverthefulltemperaturerange.UnlessotherwisespecifiedVIN=3.6V,C1=C2=1µF,C3=10µF.SymbolIQISDFSWηPOWERTSTARTRNEGVRVFBVOUTParameter

SupplyCurrent

ShutdownSupplyCurrentSwitchingFrequency(Note5)

PowerEfficiencyatVNEGStartUptime

OutputResistancetoVNEGOutputVoltageRipple(Note8)

FeedbackPinReferenceVoltage

AdjustableOutputVoltage

2.7V≤VIN≤.5.5VVIN=3.6VIL=3.6mAIL=10mA(Note6)(Note7)

IL=2.5mA,VOUT=−2.7VIL=10mA,VOUT=−3.8VIL=2.5mA(Note9)

5.5V≥VIN≥2.7V,2.5mA≥IL5.5V≥VIN≥3.0V,10mA≥IL≥0mA

0to10mA,VOUT=−2.4V5.5V≥VIN≥2.7V,IL=2.5mA

2.2

0.5

−1.25−(VIN−0.3V)−(VIN−1.2V)

51

5060

Conditions

OpenCircuit,NoLoad

Min

Typ5000.0511010594911203012−1.20

−1.15600Max9501180170

UnitsµAµAkHz%µsΩmVVV

LoadRegulationLineRegulation

VIHVILmV/mAmV/VVV

ShutdownPinInputVoltage5.5V≥VIN≥2.7VHigh

ShutdownPinInputVoltage5.5V≥VIN≥2.7VLow

Note1:AbsoluteMaximumRatingsindicatelimitsbeyondwhichdamagetothedevicemayoccur.Electricalspecificationsdonotapplywhenoperatingthedevicebeyonditsratedoperatingconditions.

Note2:OUTmaybeshortedtoGNDforonesecondwithoutdamage.However,shortingOUTtoVINmaydamagethedeviceandmustbeavoided.Also,fortemperaturesaboveTA=85˚C,OUTmustnotbeshortedtoGNDorVINordevicemaybedamaged.

Note3:Themaximumpowerdissipationmustbede-ratedatelevatedtemperaturesandislimitedbyTJMAX(maximumjunctiontemperature),TA(ambienttemperature)andθJA(junction-to-ambientthermalresistance).Themaximumpowerdissipationatanytemperatureis:

PDissMAX=(TJMAX—TA)/θJAuptothevaluelistedintheAbsoluteMaximumRatings.

Note4:Ratingisforthehumanbodymodel,a100pFcapacitordischargedthrougha1.5kΩresistorintoeachpin.Note5:Theoutputswitchesoperateatonehalftheoscillatorfrequency,fOSC=2fSW.Note6:Allcapacitorsare1µF.

Note7:CurrentdrawnfromVNEGpindecreasespowerefficiencyandwillincreaseoutputvoltageripple.

Note8:Inthetestcircuit,capacitorsC1andC2are1µF,C3=10µF,0.30ΩmaximumESRcapacitors.CapacitorswithhigherESRwillincreaseoutputresistance,increaseoutputvoltageripple,andreduceefficiency.

Note9:ThefeedbackresistorsR1andR2are200kΩresistors.

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LM268710118021

FIGURE1.StandardApplicationCircuitforMinimumCapacitanceValues

10118022

FIGURE2.StandardApplicationCircuitforLowOutputNoise

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LM2687TypicalPerformanceCharacteristics

OutputVoltagevs.OutputCurrent

Figure2

Unlessotherwisespecified,TA=25˚C,VOUT=−2.5V.

OutputVoltagevs.OutputCurrent

Figure1

10118004

10118005

OutputVoltagevs.InputVoltageMaximumOutputCurrentvs.InputVoltage

1011800610118007

MaximumVNEGCurrentvs.InputVoltage

NoLoadSupplyCurrentvs.InputVoltage

1011800810118009

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LM2687TypicalPerformanceCharacteristicsUnlessotherwisespecified,TA=25˚C,

VOUT=−2.5V.(Continued)

Start-UpTimevs.InputVoltage

Figure1

SwitchingFrequencyvs.InputVoltage

1011801010118011

Start-UpfromShutdown(noload)

Figure2OutputRippleFigure1

10118012

10118013

OutputRippleFigure2

LineTransientResponse

1011801410118017

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LM2687TypicalPerformanceCharacteristicsUnlessotherwisespecified,TA=25˚C,

VOUT=−2.5V.(Continued)

LoadTransientResponse

VFBvs.Temperature

10118018

10118015

OutputNoiseSpectrum

Figure1OutputNoiseSpectrum

Figure2

1011802410118023

10118003

FIGURE3.FunctionalBlockDiagram

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LM2687DeviceDescription

TheLM2687isaninverting,regulatedcharge-pumppowerconverter.Itfeatureslownoise,smallphysicalsize,andissimpletouse.ItisanidealsolutionforbiasingGaAsFETdevicessuchaspoweramplifiermodulesfoundinportabledevicesandcellularphones.

Aswitchedcapacitorcharge-pumpcircuitisusedtoinverttheinputvoltageVINtoitscorrespondingnegativevaluewhichisseenatVNEG.ThisvoltageisregulatedbyalowdropoutlinearregulatoratVOUT(Figure3).Theoutputvolt-agecanberegulatedanywherefrom−1.5Vto−5.2Vandisdeterminedbyapairoffeedbackresistors(seeSettingtheOutputVoltage).ThePSRRofthelinearregulatorreducestheoutputvoltagerippleproducedbythecharge-pumpin-verterto1mVP-P(typical)attheoutputVOUT.TheregulatoralsoattenuatesnoisefromtheincomingsupplyduetoitshighPSRR.

Theswitchingfrequencyisfixedat100kHzandRSW(thecombinedresistanceoftheinternalswitches)istypically10Ω.ItisclearfromthisequationthatlowESRcapacitorsaredesirableandthatlargervaluesofC1willfurtherreducetheoutputresistance.Theoutputresistanceoftheentirecircuit(indropout)is:

ROUT=RNEG+RregulatorRregulator(theoutputimpedanceofthelinearregulator)isapproximately10Ω.Whenthecircuitisinregulation,theoveralloutputresistanceisequaltothelinearregulatorloadregulation(5mV/mA).Thedropoutvoltageisthereforeaf-fectedbythecapacitorsusedsinceitissimplydefinedasIOUT*ROUT.

AlargervalueofcapacitorandlowerESRforC2willlowertheoutputvoltagerippleofthecharge-pump.ThisripplewillthenbesubjecttothePSRRofthelinearregulatorandreducedatVOUT.AlargervalueandlowerESRforC3willfurtherreducethisripple.

TheLowDropoutLinearRegulatorusesanN-channelFETdevicewhichbehavessimilarlytoanNPNdevice.BecauseofthisandtheinternalcompensationtherearenostrictESRrequirementsfortheoutputcapacitortomaintainstability.Usingtheminimumrecommendedvalueswillensurestabil-ityunderallconditions.

Insummation,largervaluecapacitorswithlowerESRwillgivethelowestoutputnoiseandripple.C1,C2,andC3shouldbe1.0µFminimumwithlessthan0.3ΩESR.Largervaluesmaybeusedforanyorallcapacitors.Allcapacitorsshouldbeeitherceramic,surface-mountchiptantalum,orpolymerelectrolytic.

OUTPUTNOISEANDRIPPLE

LowoutputnoiseandoutputvoltageripplearetwooftheattractivefeaturesoftheLM2687.Becausetheyaresmall,thenoiseandripple(1mVtyp.)canbehardtomeasureaccurately.Groundlooperrorbetweenthecircuitandtheoscilloscopecausedbytheswitchingofthecharge-pumpproducesgroundcurrentsintheprobewires.Thiscausessharpvoltagespikesontheoscilloscopewaveform.Tore-ducethiserrormeasure,theoutputdirectlyattheoutputcapacitor(C3)andusetheshortestwirespossible.Also,donotusethegroundleadontheprobe.TakethetipcoveroffoftheprobeandtouchthegroundingringoftheprobedirectlytothegroundterminalofC3.Thisshouldgivethemostaccuratereadingoftheactualoutputwaveform.

Shutdown

TheLM2687featuresalogic-levelshutdownfeature.Thefunctionisactive-lowandwillreducethesupplycurrentto0.05µA(typical)whenengaged.WhenshutdownisactiveVOUTandVNEGareswitchedtoground.

ApplicationInformation

SETTINGTHEOUTPUTVOLTAGE

TheoutputvoltageontheLM2687issetbyusingaresistordividerbetweentheoutput,thefeedbackpin,andanarbi-traryvoltageVADJ(Figure3).VADJcanrangefromGNDtoanypositivevoltageuptoVIN.VADJisusuallychosentobeGNDandshouldnotbeconnectedtoadifferentvoltageunlessitiswellregulatedsotheoutputwillstayconstant.ThefeedbackpinisheldataconstantvoltageVFBwhichequals−1.2V.Theoutputvoltagecanbeselectedusingtheequation:

ThecurrentintothefeedbackpinIFBisintherangeof10nAto100nA.Thereforeusingavalueof500kΩorsmallerforR1shouldmakethiscurrentoflittleconcernwhensettingtheoutputvoltage.Forbestaccuracy,useresistorswith1%orbettertolerance.

CAPACITORSELECTION

Selectingtherightcapacitorsforyourcircuitisimportant.Thecapacitorsaffecttheoutputresistanceofthecharge-pump,theoutputvoltageripple,andtheoveralldropoutvoltage(VIN-|VOUT|)ofthecircuit.Theoutputresistanceofthecharge-pumpinverteris:

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LM2687PhysicalDimensions

inches(millimeters)unlessotherwisenoted

MSOP-8Package8-LeadMiniSO-8(MM)

ForOrdering,RefertoOrderingInformationTable

NSPackageNumberMUA08A

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LM2687LowNoiseRegulatedSwitchedCapacitorVoltageInverterPhysicalDimensions

inches(millimeters)unlessotherwisenoted(Continued)

LLP-8Package

8-LeadLeadlessLeadframePackage(LD)ForOrdering,RefertoOrderingInformationTable

NSPackageNumberLDA08A

LIFESUPPORTPOLICY

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