LM2587数据手册

LM2587

SIMPLESWITCHER®5AFlybackRegulator

GeneralDescription

TheLM2587seriesofregulatorsaremonolithicintegratedcircuitsspecificallydesignedforflyback,step-up(boost),andforwardconverterapplications.Thedeviceisavailablein4differentoutputvoltageversions:3.3V,5.0V,12V,andad-justable.

Requiringaminimumnumberofexternalcomponents,theseregulatorsarecosteffective,andsimpletouse.Includedinthedatasheetaretypicalcircuitsofboostandflybackregu-lators.Alsolistedareselectorguidesfordiodesandcapaci-torsandafamilyofstandardinductorsandflybacktrans-formersdesignedtoworkwiththeseswitchingregulators.Thepowerswitchisa5.0ANPNdevicethatcanstand-off65V.Protectingthepowerswitcharecurrentandthermallimitingcircuits,andanundervoltagelockoutcircuit.ThisICcontainsa100kHzfixed-frequencyinternaloscillatorthatpermitstheuseofsmallmagnetics.Otherfeaturesincludesoftstartmodetoreducein-rushcurrentduringstartup,currentmodecontrolforimprovedrejectionofinputvoltageandoutputloadtransientsandcycle-by-cyclecurrentlimit-ing.Anoutputvoltagetoleranceof±4%,withinspecifiedinputvoltagesandoutputloadconditions,isguaranteedforthepowersupplysystem.

Features

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Requiresfewexternalcomponents

FamilyofstandardinductorsandtransformersNPNoutputswitches5.0A,canstandoff65VWideinputvoltagerange:4Vto40V

Current-modeoperationforimprovedtransientresponse,lineregulation,andcurrentlimit100kHzswitchingfrequency

Internalsoft-startfunctionreducesin-rushcurrentduringstart-up

Outputtransistorprotectedbycurrentlimit,undervoltagelockout,andthermalshutdown

SystemOutputVoltageToleranceof±4%maxoverlineandloadconditions

TypicalApplications

nnnn

Flybackregulator

Multiple-outputregulatorSimpleboostregulatorForwardconverter

FlybackRegulator

01231601

OrderingInformation

PackageType

5-LeadTO-220Bent,StaggeredLeads5-LeadTO-263

5-LeadTO-263TapeandReel

NSCPackageDrawingT05DTS5BTS5B

LM2587T-3.3,LM2587T-5.0,LM2587T-12,LM2587T-ADJLM2587S-3.3,LM2587S-5.0,LM2587S-12,LM2587S-ADJLM2587SX-3.3,LM2587SX-5.0,LM2587SX-12,LM2587SX-ADJ

OrderNumber

SIMPLESWITCHER®andSwitchersMadeSimple®areregisteredtrademarksofNationalSemiconductorCorporation.

©2004NationalSemiconductorCorporationDS012316www.national.com

LM2587AbsoluteMaximumRatings(Note1)

IfMilitary/Aerospacespecifieddevicesarerequired,pleasecontacttheNationalSemiconductorSalesOffice/Distributorsforavailabilityandspecifications.InputVoltageSwitchVoltageSwitchCurrent(Note2)CompensationPinVoltageFeedbackPinVoltageStorageTemperatureRangeLeadTemperature(Soldering,10sec.)

260˚C

−0.4V≤VIN≤45V−0.4V≤VSW≤65VInternallyLimited−0.4V≤VCOMP≤2.4V−0.4V≤VFB≤2VOUT−65˚Cto+150˚C

MaximumJunctionTemperature(Note3)PowerDissipation(Note3)MinimumESDRating(C=100pF,R=1.5kΩ

2kV150˚C

InternallyLimited

OperatingRatings

SupplyVoltageOutputSwitchVoltageOutputSwitchCurrentJunctionTemperatureRange

4V≤VIN≤40V0V≤VSW≤60V

ISW≤5.0A

−40˚C≤TJ≤+125˚C

LM2587-3.3

ElectricalCharacteristics

SpecificationswithstandardtypefaceareforTJ=25˚C,andthoseinboldtypefaceapplyoverfullOperatingTemperatureRange.Unlessotherwisespecified,VIN=5V.SymbolVOUT∆VOUT/∆VIN∆VOUT/∆ILOADηVREF∆VREFGMAVOLEfficiencyOutputReferenceVoltage

ReferenceVoltageLineRegulationErrorAmpTransconductanceErrorAmpVoltageGain

ICOMP=−30µAto+30µAVCOMP=1.0VVCOMP=0.5Vto1.6VRCOMP=1.0MΩ(Note6)

260

151/75

V/V

1.193

0.678

2.259

mmho

LoadRegulation

ParametersOutputVoltageLineRegulation

Conditions

VIN=4Vto12V

ILOAD=400mAto1.75AVIN=4Vto12VILOAD=400mAVIN=12V

ILOAD=400mAto1.75AVIN=12V,ILOAD=1AMeasuredatFeedbackPinVCOMP=1.0VVIN=4Vto40V

2.0

mV

753.3

3.242/3.234

3.358/3.366

%V

20

50/100

mV

20

50/100

mV

Typical3.3

Min3.17/3.14

Max3.43/3.46

UnitsV

SYSTEMPARAMETERSTestCircuitofFigure2(Note4)

UNIQUEDEVICEPARAMETERS(Note5)

LM2587-5.0

ElectricalCharacteristics

SpecificationswithstandardtypefaceareforTJ=25˚C,andthoseinboldtypefaceapplyoverfullOperatingTemperatureRange.Unlessotherwisespecified,VIN=5V.SymbolVOUT∆VOUT/∆VIN∆VOUT/∆ILOADηVREFEfficiencyOutputReferenceLoadRegulation

ParametersOutputVoltageLineRegulation

Conditions

VIN=4Vto12V

ILOAD=500mAto1.45AVIN=4Vto12VILOAD=500mAVIN=12V

ILOAD=500mAto1.45AVIN=12V,ILOAD=750mAMeasuredatFeedbackPin

805.0

4.913/4.900

5.088/5.100

%V

20

50/100

mV

20

50/100

mV

Typical5.0

Min4.80/4.75

Max5.20/5.25

UnitsV

SYSTEMPARAMETERSTestCircuitofFigure2(Note4)

UNIQUEDEVICEPARAMETERS(Note5)

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LM2587LM2587-5.0

ElectricalCharacteristics

Symbol∆VREFGMAVOLParametersVoltage

ReferenceVoltageLineRegulationErrorAmpTransconductanceErrorAmpVoltageGain

(Continued)Conditions

Typical3.30.750165

0.44799/49

1.491

Min

Max

UnitsmVmmhoV/V

VCOMP=1.0VVIN=4Vto40V

ICOMP=−30µAto+30µAVCOMP=1.0VVCOMP=0.5Vto1.6VRCOMP=1.0MΩ(Note6)

LM2587-12

ElectricalCharacteristics

SpecificationswithstandardtypefaceareforTJ=25˚C,andthoseinboldtypefaceapplyoverfullOperatingTemperatureRange.Unlessotherwisespecified,VIN=5V.SymbolVOUT∆VOUT/∆VIN∆VOUT/∆ILOADηVREF∆VREFGMAVOLEfficiencyOutputReferenceVoltage

ReferenceVoltageLineRegulationErrorAmpTransconductanceErrorAmpVoltageGain

ICOMP=−30µAto+30µAVCOMP=1.0VVCOMP=0.5Vto1.6VRCOMP=1.0MΩ(Note6)

70

41/21

V/V

0.328

0.186

0.621

mmho

LoadRegulation

ParametersOutputVoltageLineRegulation

Conditions

VIN=4Vto10VILOAD=300mAto1.2AVIN=4Vto10VILOAD=300mAVIN=10V

ILOAD=300mAto1.2AVIN=10V,ILOAD=1AMeasuredatFeedbackPinVCOMP=1.0VVIN=4Vto40V

7.8

mV

9012.0

11.79/11.76

12.21/12.24

%V

20

100/200

mV

20

100/200

mV

Typical12.0

Min11.52/11.40

Max12.48/12.60

UnitsV

SYSTEMPARAMETERSTestCircuitofFigure3(Note4)

UNIQUEDEVICEPARAMETERS(Note5)

LM2587-ADJ

ElectricalCharacteristics

SpecificationswithstandardtypefaceareforTJ=25˚C,andthoseinboldtypefaceapplyoverfullOperatingTemperatureRange.Unlessotherwisespecified,VIN=5V.SymbolVOUT∆VOUT/∆VIN∆VOUT/∆ILOADηVREFEfficiencyOutputReferenceVoltage

LoadRegulation

ParametersOutputVoltageLineRegulation

Conditions

VIN=4Vto10VILOAD=300mAto1.2AVIN=4Vto10VILOAD=300mAVIN=10V

ILOAD=300mAto1.2AVIN=10V,ILOAD=1AMeasuredatFeedbackPinVCOMP=1.0V

901.230

1.208/1.205

1.252/1.255

%V

20

100/200

mV

20

100/200

mV

Typical12.0

Min11.52/11.40

Max12.48/12.60

UnitsV

SYSTEMPARAMETERSTestCircuitofFigure3(Note4)

UNIQUEDEVICEPARAMETERS(Note5)

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LM2587LM2587-ADJ

ElectricalCharacteristics

Symbol∆VREFGMAVOLIBParametersReferenceVoltageLineRegulationErrorAmpTransconductanceErrorAmpVoltageGainErrorAmpInputBiasCurrent

(Continued)Conditions

Typical1.53.200670125

1.800400/200

425/6006.000

Min

Max

UnitsmVmmhoV/VnA

VIN=4Vto40V

ICOMP=−30µAto+30µAVCOMP=1.0VVCOMP=0.5Vto1.6VRCOMP=1.0MΩ(Note6)VCOMP=1.0V

AllOutputVoltageVersionsElectricalCharacteristics(Note5)

SpecificationswithstandardtypefaceareforTJ=25˚C,andthoseinboldtypefaceapplyoverfullOperatingTemperatureRange.Unlessotherwisespecified,VIN=5V.SymbolISParametersInputSupplyCurrent

(SwitchOff)(Note8)ISWITCH=3.0A

VUVfOInputSupply

UndervoltageLockoutOscillatorFrequency

MeasuredatSwitchPinRLOAD=100ΩVCOMP=1.0V

fSCShort-CircuitFrequency

VEAOErrorAmplifierOutputSwing

MeasuredatSwitchPinRLOAD=100ΩVFEEDBACK=1.15VUpperLimit(Note7)LowerLimit(Note8)

IEAOErrorAmpOutputCurrent(SourceorSink)

ISSDILVSUSVSATICLSoftStartCurrentMaximumDutyCycleSwitchLeakageCurrent

SwitchSustainingVoltage

SwitchSaturationVoltageNPNSwitchCurrentLimit

COMMONDEVICEPARAMETERS(Note4)θJAθJAθJCwww.national.com

ConditionsTypical11853.30

MinMax15.5/16.5140/165

UnitsmAmAV

RLOAD=100Ω

3.053.75

10085/75115/125kHz

252.80.25

2.6/2.4

0.40/0.55

kHzVV

(Note9)

165

VFEEDBACK=0.92VVCOMP=1.0VRLOAD=100Ω(Note7)SwitchOffVSWITCH=60VdV/dT=1.5V/nsISWITCH=5.0A

0.76.5

5.065

1.1/1.49.5

VVA

15

300/600

µA

98

93/90

%

11.0

110/708.0/7.0

260/32017.0/19.0

µAµA

ThermalResistanceTPackage,JunctiontoAmbient(Note10)TPackage,JunctiontoAmbient(Note11)TPackage,JunctiontoCase

4

652

LM2587AllOutputVoltageVersionsElectricalCharacteristics(Note

SymbolθJAθJAθJAθJCParameters

5)(Continued)Conditions

Typical5635262

Min

Max

Units˚C/W

SPackage,JunctiontoAmbient(Note12)SPackage,JunctiontoAmbient(Note13)SPackage,JunctiontoAmbient(Note14)SPackage,JunctiontoCase

Note1:AbsoluteMaximumRatingsindicatelimitsbeyondwhichdamagetothedevicemayoccur.Operatingratingsindicateconditionsthedeviceisintendedtobefunctional,butdeviceparameterspecificationsmaynotbeguaranteedundertheseconditions.Forguaranteedspecificationsandtestconditions,seetheElectricalCharacteristics.

Note2:Notethatswitchcurrentandoutputcurrentarenotidenticalinastep-upregulator.OutputcurrentcannotbeinternallylimitedwhentheLM2587isusedasastep-upregulator.Topreventdamagetotheswitch,theoutputcurrentmustbeexternallylimitedto5A.However,outputcurrentisinternallylimitedwhentheLM2587isusedasaflybackregulator(seetheApplicationHintssectionformoreinformation).

Note3:Thejunctiontemperatureofthedevice(TJ)isafunctionoftheambienttemperature(TA),thejunction-to-ambientthermalresistance(θJA),andthepowerdissipationofthedevice(PD).Athermalshutdownwilloccurifthetemperatureexceedsthemaximumjunctiontemperatureofthedevice:PDxθJA+TA(MAX)≥TJ(MAX).Forasafethermaldesign,checkthatthemaximumpowerdissipatedbythedeviceislessthan:PD≤[TJ(MAX)−TA(MAX))]/θJA.Whencalculatingthemaximumallowablepowerdissipation,deratethemaximumjunctiontemperature—thisensuresamarginofsafetyinthethermaldesign.

Note4:Externalcomponentssuchasthediode,inductor,inputandoutputcapacitorscanaffectswitchingregulatorperformance.WhentheLM2587isusedasshowninFigure2andFigure3,systemperformancewillbeasspecifiedbythesystemparameters.

Note5:Allroomtemperaturelimitsare100%productiontested,andalllimitsattemperatureextremesareguaranteedviacorrelationusingstandardStatisticalQualityControl(SQC)methods.

Note6:A1.0MΩresistorisconnectedtothecompensationpin(whichistheerroramplifieroutput)toensureaccuracyinmeasuringAVOL.

Note7:Tomeasurethisparameter,thefeedbackvoltageissettoalowvalue,dependingontheoutputversionofthedevice,toforcetheerroramplifieroutputhigh.Adj:VFB=1.05V;3.3V:VFB=2.81V;5.0V:VFB=4.25V;12V:VFB=10.20V.

Note8:Tomeasurethisparameter,thefeedbackvoltageissettoahighvalue,dependingontheoutputversionofthedevice,toforcetheerroramplifieroutputlow.Adj:VFB=1.41V;3.3V:VFB=3.80V;5.0V:VFB=5.75V;12V:VFB=13.80V.

Note9:Tomeasuretheworst-caseerroramplifieroutputcurrent,theLM2587istestedwiththefeedbackvoltagesettoitslowvalue(specifiedinNote7)andatitshighvalue(specifiedinNote8).

Note10:Junctiontoambientthermalresistance(noexternalheatsink)forthe5leadTO-220packagemountedvertically,with1⁄2inchleadsinasocket,oronaPCboardwithminimumcopperarea.

Note11:Junctiontoambientthermalresistance(noexternalheatsink)forthe5leadTO-220packagemountedvertically,with1⁄2inchleadssolderedtoaPCboardcontainingapproximately4squareinchesof(1oz.)copperareasurroundingtheleads.

Note12:Junctiontoambientthermalresistanceforthe5leadTO-263mountedhorizontallyagainstaPCboardareaof0.136squareinches(thesamesizeastheTO-263package)of1oz.(0.0014in.thick)copper.

Note13:Junctiontoambientthermalresistanceforthe5leadTO-263mountedhorizontallyagainstaPCboardareaof0.46squareinches(3.6timestheareaoftheTO-263package)of1oz.(0.0014in.thick)copper.

Note14:Junctiontoambientthermalresistanceforthe5leadTO-263mountedhorizontallyagainstaPCboardcopperareaof1.00squareinches(7.4timestheareaoftheTO-263package)of1oz.(0.0014in.thick)copper.Additionalcopperareawillreducethermalresistancefurther.SeethethermalmodelinSwitchersMadeSimple®software.

TypicalPerformanceCharacteristics

SupplyCurrentvsTemperature

ReferenceVoltagevsTemperature

012318012319

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LM2587TypicalPerformanceCharacteristics

∆ReferenceVoltagevsSupplyVoltage

(Continued)

SupplyCurrentvsSwitchCurrent

0123165001231651

CurrentLimitvsTemperatureFeedbackPinBiasCurrentvsTemperature

0123165201231653

SwitchSaturationVoltagevsTemperatureSwitchTransconductance

vsTemperature

01231601231655

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LM2587TypicalPerformanceCharacteristics

OscillatorFrequencyvsTemperature

(Continued)

ErrorAmpTransconductance

vsTemperature

0123165601231657

ErrorAmpVoltageGainvsTemperatureShortCircuitFrequency

vsTemperature

0123165801231659

ConnectionDiagrams

Bent,StaggeredLeads5-LeadTO-220(T)

TopView

Bent,StaggeredLeads5-LeadTO-220(T)

SideView

01231604

01231603

OrderNumberLM2587T-3.3,LM2587T-5.0,

LM2587T-12orLM2587T-ADJSeeNSPackageNumberT05D

5-LeadTO-263(S)

TopView

5-LeadTO-263(S)

SideView

01231606

01231605

OrderNumberLM2587S-3.3,LM2587S-5.0,

LM2587S-12orLM2587S-ADJSeeNSPackageNumberTS5B

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LM2587BlockDiagram

01231607

ForFixedVersions3.3V,R1=3.4k,R2=2k5V,R1=6.15k,R2=2k12V,R1=8.73k,R2=1kForAdj.VersionR1=Short(0Ω),R2=Open

FIGURE1.

TestCircuits

01231608

CIN1—100µF,25VAluminumElectrolyticCIN2—0.1µFCeramicT—22µH,1:1Schott#67141450D—1N5820COUT—680µF,16VAluminumElectrolyticCC—0.47µFCeramicRC—2k

FIGURE2.LM2587-3.3andLM2587-5.0

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LM2587TestCircuits

(Continued)

01231609

CIN1—100µF,25VAluminumElectrolyticCIN2—0.1µFCeramicL—15µH,Renco#RL-72-5D—1N5820COUT—680µF,16VAluminum

ElectrolyticCC—0.47µFCeramicRC—2kFor12VDevices:R1=Short(0Ω)andR2=OpenForADJDevices:R1=48.75k,±0.1%andR2=5.62k,±1%

FIGURE3.LM2587-12andLM2587-ADJ

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LM2587FlybackRegulatorOperation

TheLM2587isideallysuitedforuseintheflybackregulatortopology.Theflybackregulatorcanproduceasingleoutputvoltage,suchastheoneshowninFigure4,ormultipleoutputvoltages.InFigure4,theflybackregulatorgeneratesanoutputvoltagethatisinsidetherangeoftheinputvoltage.Thisfeatureisuniquetoflybackregulatorsandcannotbeduplicatedwithbuckorboostregulators.

Theoperationofaflybackregulatorisasfollows(refertoFigure4):whentheswitchison,currentflowsthroughtheprimarywindingofthetransformer,T1,storingenergyinthemagneticfieldofthetransformer.Notethattheprimaryandsecondarywindingsareoutofphase,sonocurrentflowsthroughthesecondarywhencurrentflowsthroughthepri-mary.Whentheswitchturnsoff,themagneticfieldcol-

lapses,reversingthevoltagepolarityoftheprimaryandsecondarywindings.NowrectifierD1isforwardbiasedandcurrentflowsthroughit,releasingtheenergystoredinthetransformer.Thisproducesvoltageattheoutput.

Theoutputvoltageiscontrolledbymodulatingthepeakswitchcurrent.Thisisdonebyfeedingbackaportionoftheoutputvoltagetotheerroramp,whichamplifiesthediffer-encebetweenthefeedbackvoltageanda1.230Vreference.Theerrorampoutputvoltageiscomparedtoarampvoltageproportionaltotheswitchcurrent(i.e.,inductorcurrentdur-ingtheswitchontime).Thecomparatorterminatestheswitchontimewhenthetwovoltagesareequal,therebycontrollingthepeakswitchcurrenttomaintainaconstantoutputvoltage.

01231610

AsshowninFigure4,theLM2587canbeusedasaflybackregulatorbyusingaminimumnumberofexternalcomponents.TheswitchingwaveformsofthisregulatorareshowninFigure5.TypicalPerformanceCharacteristicsobservedduringtheoperationofthiscircuitareshowninFigure6.

FIGURE4.12VFlybackRegulatorDesignExample

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LM2587TypicalPerformanceCharacteristics

01231611

A:SwitchVoltage,10V/divB:SwitchCurrent,5A/divC:OutputRectifierCurrent,5A/divD:OutputRippleVoltage,100mV/divAC-CoupledHorizontal:2µs/div

FIGURE5.SwitchingWaveforms

01231612

FIGURE6.VOUTLoadCurrentStepResponse

TypicalFlybackRegulatorApplications

Figures7,8,9,11,12showsixtypicalflybackapplications,varyingfromsingleoutputtotripleoutput.Eachdrawingcontainsthepartnumber(s)andmanufacturer(s)forevery

componentexceptthetransformer.Forthetransformerpartnumbersandmanufacturersnames,seethetableinFigure13.Forapplicationswithdifferentoutputvoltages—requiringtheLM2587-ADJ—ordifferentoutputconfigurationsthatdonotmatchthestandardconfigurations,refertotheSwitchersMadeSimplesoftware.

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LM2587TypicalFlybackRegulatorApplications

(Continued)

01231613

FIGURE7.Single-OutputFlybackRegulator

01231614

FIGURE8.Single-OutputFlybackRegulator

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LM2587TypicalFlybackRegulatorApplications

(Continued)

01231615

FIGURE9.Single-OutputFlybackRegulator

01231616

FIGURE10.Dual-OutputFlybackRegulator

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LM2587TypicalFlybackRegulatorApplications

(Continued)

01231617

FIGURE11.Dual-OutputFlybackRegulator

01231618

FIGURE12.Triple-OutputFlybackRegulator

TRANSFORMERSELECTION(T)

Figure13liststhestandardtransformersavailableforfly-backregulatorapplications.Includedinthetablearetheturnsratio(s)foreachtransformer,aswellastheoutputvoltages,inputvoltageranges,andthemaximumloadcur-rentsforeachcircuit.

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LM2587TypicalFlybackRegulatorApplications

ApplicationsTransformersVINVOUT1IOUT1(Max)N1VOUT2IOUT2(Max)N2VOUT3IOUT3(Max)N3Figure7T14V–6V3.3V1.8A1

Figure8T14V–6V5V1.4A1

(Continued)

Figure9T18V–16V12V1.2A1

Figure10

T24V–6V12V0.3A2.5−12V0.3A2.5

Figure11

T318V–36V12V1A0.8−12V1A0.8

Figure12

T418V–36V5V2.5A0.3512V0.5A0.8−12V0.5A0.8

FIGURE13.TransformerSelectionTable

Transformer

Type

T1T2T3T4

Note15:CoilcraftInc.,:

Manufacturers’PartNumbers

Coilcraft(Note15)Q4434-BQ4337-BQ4343-BQ4344-B

Phone:(800)322-25

Phone:(619)674-8100

Fax:(619)674-8262

Phone:(800)5-5828

Fax:(516)586-5562

Fax:(612)475-1786

Coilcraft(Note15)SurfaceMountQ4435-BQ4436-B

——

Pulse(Note16)SurfaceMountPE-68411PE-68412PE-68421PE-68422

Renco(Note17)RL-5530RL-5531RL-5534RL-5535

Schott(Note18)67141450671408606714092067140930

1102SilverLakeRoad,Cary,IL60013:Fax:(708)639-1469Note16:PulseEngineeringInc.,:Note17:RencoElectronicsInc.,:Note18:SchottCorp.,:

12220WorldTradeDrive,SanDiego,CA92128:60JeffrynBlvd.East,DeerPark,NY11729:

Phone:(612)475-1173

1000ParkersLaneRoad,Wayzata,MN55391:

FIGURE14.TransformerManufacturerGuide

TRANSFORMERFOOTPRINTS

Figures15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30,31andFigure32showthefootprintsofeachtrans-former,listedinFigure14.

T1

T2

01231631

TopView

01231630

TopView

FIGURE15.CoilcraftQ4434-B

FIGURE16.CoilcraftQ4337-B

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LM2587TypicalFlybackRegulatorApplications(Continued)

T3

T2

01231635

TopView

01231632

TopView

FIGURE17.CoilcraftQ4343-B

FIGURE20.CoilcraftQ4436-B

(SurfaceMount)

T1

T4

01231636

TopView

01231633

TopView

FIGURE18.CoilcraftQ4344-B

FIGURE21.PulsePE-68411

(SurfaceMount)

T2

T1

01231634

TopView

FIGURE19.CoilcraftQ4435-B

(SurfaceMount)

01231637

TopView

FIGURE22.PulsePE-68412

(SurfaceMount)

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LM2587TypicalFlybackRegulatorApplications(Continued)

T3

T2

012311

TopView

01231638

TopView

FIGURE23.PulsePE-68421

(SurfaceMount)

FIGURE26.RencoRL-5531

T3

T4

012316

TopView

FIGURE27.RencoRL-5534

01231639

T4

TopView

FIGURE24.PulsePE-68422

(SurfaceMount)

T1

012312

TopView

FIGURE28.RencoRL-5535

012310

TopView

T1

FIGURE25.RencoRL-5530

012313

TopView

FIGURE29.Schott67141450

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LM2587TypicalFlybackRegulatorApplications(Continued)

T2

T4

012317

012314

TopView

FIGURE30.Schott67140860

TopView

FIGURE32.Schott67140930

T3

012315

TopView

FIGURE31.Schott67140920

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LM2587Step-Up(Boost)RegulatorOperation

Figure33showstheLM2587usedasastep-up(boost)regulator.Thisisaswitchingregulatorthatproducesanoutputvoltagegreaterthantheinputsupplyvoltage.AbriefexplanationofhowtheLM2587BoostRegulatorworksisasfollows(refertoFigure33).WhentheNPNswitchturnson,theinductorcurrentrampsupattherateof

VIN/L,storingenergyintheinductor.Whentheswitchturnsoff,thelowerendoftheinductorfliesaboveVIN,dischargingitscurrentthroughdiode(D)intotheoutputcapacitor(COUT)atarateof(VOUT−VIN)/L.Thus,energystoredintheinductorduringtheswitchontimeistransferredtotheoutputduringtheswitchofftime.Theoutputvoltageiscontrolledbyadjustingthepeakswitchcurrent,asdescribedintheflybackregulatorsection.

01231619

Byaddingasmallnumberofexternalcomponents(asshowninFigure33),theLM2587canbeusedtoproducearegulatedoutputvoltagethatisgreaterthantheappliedinputvoltage.TheswitchingwaveformsobservedduringtheoperationofthiscircuitareshowninFigure34.TypicalperformanceofthisregulatorisshowninFigure35.

FIGURE33.12VBoostRegulator

TypicalPerformanceCharacteristics

01231620

A:SwitchVoltage,10V/divB:SwitchCurrent,5A/divC:InductorCurrent,5A/divD:OutputRippleVoltage,100mV/div,AC-CoupledHorizontal:2µs/div

FIGURE34.SwitchingWaveforms

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LM2587TypicalPerformanceCharacteristics

(Continued)

01231621

FIGURE35.VOUTResponsetoLoadCurrentStep

TypicalBoostRegulatorApplications

Figure36andFigures38,39andFigure40showfourtypicalboostapplications)—onefixedandthreeusingtheadjust-ableversionoftheLM2587.Eachdrawingcontainsthepart

number(s)andmanufacturer(s)foreverycomponent.Forthefixed12Voutputapplication,thepartnumbersandmanufacturers’namesfortheinductorarelistedinatableinFigure40.Forapplicationswithdifferentoutputvoltages,refertotheSwitchersMadeSimplesoftware.

01231622

FIGURE36.+5Vto+12VBoostRegulator

Figure37containsatableofstandardinductors,bypartnumberandcorrespondingmanufacturer,forthefixedout-putregulatorofFigure36.

Coilcraft(Note19)R4793-A

Note19:CoilcraftInc.,:

Phone:(800)322-25

Phone:(619)674-8100

Fax:(619)674-8262

Phone:(800)5-5828

Fax:(516)586-5562

Fax:(612)475-1786

1102SilverLakeRoad,Cary,IL60013:Fax:(708)639-1469Note20:PulseEngineeringInc.,:Note21:RencoElectronicsInc.,:Note22:SchottCorp.,:

12220WorldTradeDrive,SanDiego,CA92128:60JeffrynBlvd.East,DeerPark,NY11729:

Pulse(Note20)PE-53900

Renco(Note21)RL-72-5

Schott(Note22)67146520

Phone:(612)475-1173

1000ParkersLaneRoad,Wayzata,MN55391:

FIGURE37.InductorSelectionTable

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20

LM2587TypicalBoostRegulatorApplications

(Continued)

01231623

FIGURE38.+12Vto+24VBoostRegulator

01231624

FIGURE39.+24Vto+36VBoostRegulator

01231625

*TheLM2587willrequireaheatsinkintheseapplications.Thesizeoftheheatsinkwilldependonthemaximumambienttemperature.TocalculatethethermalresistanceoftheICandthesizeoftheheatsinkneeded,seethe“HeatSink/ThermalConsiderations”sectionintheApplicationHints.

FIGURE40.+24Vto+48VBoostRegulator

21www.national.com

LM2587ApplicationHints

01231626

FIGURE41.BoostRegulator

PROGRAMMINGOUTPUTVOLTAGE(SELECTINGR1ANDR2)

ReferringtotheadjustableregulatorinFigure41,theoutputvoltageisprogrammedbytheresistorsR1andR2bythefollowingformula:

whereVREF=1.23VVOUT=VREF(1+R1/R2)

ResistorsR1andR2dividetheoutputvoltagedownsothatitcanbecomparedwiththe1.23Vinternalreference.WithR2between1kand5k,R1is:

whereVREF=1.23VR1=R2(VOUT/VREF−1)

Forbesttemperaturecoefficientandstabilitywithtime,use1%metalfilmresistors.

SHORTCIRCUITCONDITION

Duetotheinherentnatureofboostregulators,whentheoutputisshorted(seeFigure41),currentflowsdirectlyfromtheinput,throughtheinductorandthediode,totheoutput,bypassingtheswitch.Thecurrentlimitoftheswitchdoesnotlimittheoutputcurrentfortheentirecircuit.Toprotecttheloadandpreventdamagetotheswitch,thecurrentmustbeexternallylimited,eitherbytheinputsupplyorattheoutputwithanexternalcurrentlimitcircuit.Theexternallimitshouldbesettothemaximumswitchcurrentofthedevice,whichis5A.

Inaflybackregulatorapplication(Figure42),usingthestan-dardtransformers,theLM2587willsurviveashortcircuitto

themainoutput.Whentheoutputvoltagedropsto80%ofitsnominalvalue,thefrequencywilldropto25kHz.Withalowerfrequency,offtimesarelarger.Withthelongerofftimes,thetransformercanreleaseallofitsstoredenergybeforetheswitchturnsbackon.Hence,theswitchturnsoninitiallywithzerocurrentatitscollector.Inthiscondition,theswitchcurrentlimitwilllimitthepeakcurrent,savingthedevice.

FLYBACKREGULATORINPUTCAPACITORS

Aflybackregulatordrawsdiscontinuouspulsesofcurrentfromtheinputsupply.Therefore,therearetwoinputcapaci-torsneededinaflybackregulator;oneforenergystorageandoneforfiltering(seeFigure42).Botharerequiredduetotheinherentoperationofaflybackregulator.TokeepastableorconstantvoltagesupplytotheLM2587,astoragecapacitor(≥100µF)isrequired.IftheinputsourceisarecitifiedDCsupplyand/ortheapplicationhasawidetem-peraturerange,therequiredrmscurrentratingofthecapaci-tormightbeverylarge.Thismeansalargervalueofcapaci-tanceorahighervoltageratingwillbeneededoftheinputcapacitor.Thestoragecapacitorwillalsoattenuatenoisewhichmayinterferewithothercircuitsconnectedtothesameinputsupplyvoltage.

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LM2587ApplicationHints

(Continued)

01231627

FIGURE42.FlybackRegulator

Inaddition,asmallbypasscapacitorisrequiredduetothenoisegeneratedbytheinputcurrentpulses.Toeliminatethenoise,inserta1.0µFceramiccapacitorbetweenVINandgroundascloseaspossibletothedevice.

SWITCHVOLTAGELIMITS

Inaflybackregulator,themaximumsteady-statevoltageappearingattheswitch,whenitisoff,issetbythetrans-formerturnsratio,N,theoutputvoltage,VOUT,andthemaximuminputvoltage,VIN(Max):

VSW(OFF)=VIN(Max)+(VOUT+VF)/N

whereVFistheforwardbiasedvoltageoftheoutputdiode,andis0.5VforSchottkydiodesand0.8Vforultra-fastrecov-erydiodes(typically).Incertaincircuits,thereexistsavolt-agespike,VLL,superimposedontopofthesteady-statevoltage(seeFigure5,waveformA).Usually,thisvoltagespikeiscausedbythetransformerleakageinductanceand/ortheoutputrectifierrecoverytime.To“clamp”thevoltageattheswitchfromexceedingitsmaximumvalue,atransientsuppressorinserieswithadiodeisinsertedacrossthetransformerprimary(asshowninthecircuitonthefrontpageandotherflybackregulatorcircuitsthroughoutthedatasheet).TheschematicinFigure42showsanothermethodofclampingtheswitchvoltage.Asinglevoltagetransientsuppressor(theSA51A)isinsertedattheswitchpin.Thismethodclampsthetotalvoltageacrosstheswitch,notjustthevoltageacrosstheprimary.

Ifpoorcircuitlayouttechniquesareused(seethe“CircuitLayoutGuideline”section),negativevoltagetransientsmayappearontheSwitchpin(pin4).Applyinganegativevoltage(withrespecttotheIC’sground)toanymonolithicICpincauseserraticandunpredictableoperationofthatIC.ThisholdstruefortheLM2587ICaswell.Whenusedinaflybackregulator,thevoltageattheSwitchpin(pin4)cangonega-tivewhentheswitchturnson.The“ringing”voltageatthe

23

switchpiniscausedbytheoutputdiodecapacitanceandthetransformerleakageinductanceformingaresonantcircuitatthesecondary(ies).Theresonantcircuitgeneratesthe“ring-ing”voltage,whichgetsreflectedbackthroughthetrans-formertotheswitchpin.Therearetwocommonmethodstoavoidthisproblem.OneistoaddanRCsnubberaroundtheoutputrectifier(s),asinFigure42.ThevaluesoftheresistorandthecapacitormustbechosensothatthevoltageattheSwitchpindoesnotdropbelow−0.4V.Theresistormayrangeinvaluebetween10Ωand1kΩ,andthecapacitorwillvaryfrom0.001µFto0.1µF.Addingasnubberwill(slightly)reducetheefficiencyoftheoverallcircuit.

Theothermethodtoreduceoreliminatethe“ringing”istoinsertaSchottkydiodeclampbetweenpins4and3(ground),alsoshowninFigure42.Thispreventsthevoltageatpin4fromdroppingbelow−0.4V.Thereversevoltageratingofthediodemustbegreaterthantheswitchoffvoltage.

01231628

FIGURE43.InputLineFilter

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LM2587ApplicationHints

(Continued)

OUTPUTVOLTAGELIMITATIONS

Themaximumoutputvoltageofaboostregulatoristhemaximumswitchvoltageminusadiodedrop.Inaflybackregulator,themaximumoutputvoltageisdeterminedbytheturnsratio,N,andthedutycycle,D,bytheequation:

VOUT≈NxVINxD/(1−D)Thedutycycleofaflybackregulatorisdeterminedbythefollowingequation:

ThecircuitinFigure43demonstratesthelayoutofthefilter,withthecapacitorplacedfromtheinputpintogroundandtheresistorplacedbetweentheinputsupplyandtheinputpin.NotethatthevaluesofRINandCINshowninthesche-maticaregoodenoughformostapplications,butsomereadjustingmightberequiredforaparticularapplication.Ifefficiencyisamajorconcern,replacetheresistorwithasmallinductor(say10µHandratedat100mA).STABILITY

Allcurrent-modecontrolledregulatorscansufferfromaninstability,knownassubharmonicoscillation,iftheyoperatewithadutycycleabove50%.Toeliminatesubharmonicoscillations,aminimumvalueofinductanceisrequiredtoensurestabilityforallboostandflybackregulators.Theminimuminductanceisgivenby:

Theoretically,themaximumoutputvoltagecanbeaslargeasdesired—justkeepincreasingtheturnsratioofthetrans-former.However,thereexistssomephysicallimitationsthatpreventtheturnsratio,andthustheoutputvoltage,fromincreasingtoinfinity.Thephysicallimitationsarecapaci-tancesandinductancesintheLM2587switch,theoutputdiode(s),andthetransformer—suchasreverserecoverytimeoftheoutputdiode(mentionedabove).

NOISYINPUTLINECONDITION)

Asmall,low-passRCfiltershouldbeusedattheinputpinoftheLM2587iftheinputvoltagehasanunusuallargeamountoftransientnoise,suchaswithaninputswitchthatbounces.

whereVSATistheswitchsaturationvoltageandcanbefoundintheCharacteristicCurves.

01231629

FIGURE44.CircuitBoardLayout

CIRCUITLAYOUTGUIDELINES

Asinanyswitchingregulator,layoutisveryimportant.Rap-idlyswitchingcurrentsassociatedwithwiringinductancegeneratevoltagetransientswhichcancauseproblems.Forminimalinductanceandgroundloops,keepthelengthoftheleadsandtracesasshortaspossible.Usesinglepointgroundingorgroundplaneconstructionforbestresults.Separatethesignalgroundsfromthepowergrounds(asindicatedinFigure44).WhenusingtheAdjustableversion,physicallylocatetheprogrammingresistorsasneartheregulatorICaspossible,tokeepthesensitivefeedbackwiringshort.

HEATSINK/THERMALCONSIDERATIONS

Inmanycases,noheatsinkisrequiredtokeeptheLM2587junctiontemperaturewithintheallowedoperatingrange.Foreachapplication,todeterminewhetherornotaheatsinkwillberequired,thefollowingmustbeidentified:

1)Maximumambienttemperature(intheapplication).2)Maximumregulatorpowerdissipation(intheapplication).3)Maximumallowedjunctiontemperature(125˚CfortheLM2587).Forasafe,conservativedesign,atemperatureapproximately15˚Ccoolerthanthemaximumjunctiontem-peratureshouldbeselected(110˚C).

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LM2587ApplicationHints

(Continued)

4)LM2587packagethermalresistancesθJAandθJC(givenintheElectricalCharacteristics).

Totalpowerdissipated(PD)bytheLM2587canbeestimatedasfollows:Boost:

Iftheoperatingjunctiontemperatureexceedsthemaximumjunctiontemperatueinitem3above,thenaheatsinkisrequired.Whenusingaheatsink,thejunctiontemperaturerisecanbedeterminedbythefollowing:

∆TJ=PDx(θJC+θInterface+θHeatSink)Again,theoperatingjunctiontemperaturewillbe:

TJ=∆TJ+TAAsbefore,ifthemaximumjunctiontemperatureisexceeded,alargerheatsinkisrequired(onethathasalowerthermalresistance).

IncludedintheSwitchersMadeSimpledesignsoftwareisamoreprecise(non-linear)thermalmodelthatcanbeusedtodeterminejunctiontemperaturewithdifferentinput-outputparametersordifferentcomponentvalues.Itcanalsocalcu-latetheheatsinkthermalresistancerequiredtomaintaintheregulatorjunctiontemperaturebelowthemaximumoperat-ingtemperature.

VINistheminimuminputvoltage,VOUTistheoutputvoltage,Nisthetransformerturnsratio,Disthedutycycle,andILOADisthemaximumloadcurrent(and∑ILOADisthesumofthemaximumloadcurrentsformultiple-outputflybackregula-tors).Thedutycycleisgivenby:Boost:

Tofurthersimplifytheflybackregulatordesignprocedure,NationalSemiconductorismakingavailablecomputerde-signsoftware.SwitchersMadeSimplesoftwareisavailableona(31⁄2\")disketteforIBMcompatablecomputersfromaNationalSemiconductorsalesofficeinyourareaortheNationalSemiconductorCustomerResponseCenter(1-800-272-9959).

EuropeanMagneticVendorContacts

Pleasecontactthefollowingaddressesfordetailsoflocaldistributorsorrepresentatives:

whereVFistheforwardbiasedvoltageofthediodeandistypically0.5VforSchottkydiodesand0.8Vforfastrecoverydiodes.VSATistheswitchsaturationvoltageandcanbefoundintheCharacteristicCurves.

Whennoheatsinkisused,thejunctiontemperatureriseis:

∆TJ=PDxθJA.

Addingthejunctiontemperaturerisetothemaximumambi-enttemperaturegivestheactualoperatingjunctiontempera-ture:

TJ=∆TJ+TA.

Coilcraft

21NapierPlace

WardparkNorthCumbernauld,ScotlandG680LLPhone:+441236730595Fax:+441236730627

PulseEngineering

DunmoreRoad

TuamCo.Galway,IrelandPhone:+3539324107Fax:+3539324459

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LM2587PhysicalDimensions

unlessotherwisenoted

inches(millimeters)

OrderNumberLM2587T-3.3,LM2587T-5.0,

LM2587T-12orLM2587T-ADJNSPackageNumberT05D

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LM2587SIMPLESWITCHER5AFlybackRegulatorPhysicalDimensions

inches(millimeters)unlessotherwisenoted(Continued)

OrderNumberLM2587S-3.3,LM2587S-5.0,

LM2587S-12orLM2587S-ADJNSPackageNumberTS5B

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