开关稳压芯片-LM2577

LM1577󰁋LM2577Series

SIMPLESWITCHER󰀃Step-UpVoltageRegulator

GeneralDescription

TheLM1577󰁋LM2577aremonolithicintegratedcircuitsthatprovideallofthepowerandcontrolfunctionsforstep-up(boost)󰀷flyback󰀷andforwardconverterswitchingregulators󰀟Thedeviceisavailableinthreedifferentoutputvoltagever-sions󰀌12V󰀷15V󰀷andadjustable󰀟

Requiringaminimumnumberofexternalcomponents󰀷theseregulatorsarecosteffective󰀷andsimpletouse󰀟Listedinthisdatasheetareafamilyofstandardinductorsandflybacktransformersdesignedtoworkwiththeseswitchingregulators󰀟

Includedonthechipisa3󰀟0ANPNswitchanditsassociat-edprotectioncircuitry󰀷consistingofcurrentandthermallim-iting󰀷andundervoltagelockout󰀟Otherfeaturesincludea52kHzfixed-frequencyoscillatorthatrequiresnoexternalcom-ponents󰀷asoftstartmodetoreducein-rushcurrentduringstart-up󰀷andcurrentmodecontrolforimprovedrejectionofinputvoltageandoutputloadtransients󰀟

Features

YYYY

YY

Y

Requiresfewexternalcomponents

NPNoutputswitches3󰀟0A󰀷canstandoff65VWideinputvoltagerange󰀌3󰀟5Vto40V

Current-modeoperationforimprovedtransientresponse󰀷lineregulation󰀷andcurrentlimit52kHzinternaloscillator

Soft-startfunctionreducesin-rushcurrentduringstart-up

Outputswitchprotectedbycurrentlimit󰀷under-voltagelockout󰀷andthermalshutdown

TypicalApplications

YYY

Simpleboostregulator

FlybackandforwardregulatorsMultiple-outputregulator

TypicalApplication

Note󰀌PinnumbersshownareforTO-220(T)package󰀟

TL󰁋H󰁋11468–1

OrderingInformation

Temperature

Range

PackageType

OutputVoltage

12V

15V

ADJ

NSC

PackagePackageDrawing

SONTO-263TO-220TO-220TO-3

b40󰀄CsTAsa125󰀄C24-PinSurfaceMount

LM2577M-12LM2577M-15LM2577M-ADJM24B

16-PinMoldedDIPLM2577N-12LM2577N-15LM2577N-ADJN16A5-LeadSurfaceMountLM2577S-12LM2577S-15LM2577S-ADJTS5B5-StraightLeadsLM2577T-12LM2577T-15LM2577T-ADJT05A5-BentStaggeredLeadsLM2577T-12LM2577T-15LM2577T-ADJT05D

FlowLB03FlowLB03FlowLB03

b55󰀄CsTAsa150󰀄C4-PinTO-3LM1577K-12󰁋883LM1577K-15󰁋883LM1577K-ADJ󰁋883K04A

SIMPLESWITCHER󰀃isaregisteredtrademarkofNationalSemiconductorCorporation󰀟C1995NationalSemiconductorCorporation

TL󰁋H󰁋11468

RRD-B30M75󰁋PrintedinU󰀟S󰀟A󰀟

(Note1)

IfMilitary󰁋Aerospacespecifieddevicesarerequired󰀷pleasecontacttheNationalSemiconductorSalesOffice󰁋Distributorsforavailabilityandspecifications󰀟SupplyVoltageOutputSwitchVoltageOutputSwitchCurrent(Note2)PowerDissipation

StorageTemperatureRange

LeadTemperature(Soldering󰀷10sec󰀟)MaximumJunctionTemperatureMinimumESDRating

(Ce100pF󰀷Re1󰀟5kX)

45V65V6󰀟0A

InternallyLimited

b65󰀄Ctoa150󰀄C

AbsoluteMaximumRatingsOperatingRatings

SupplyVoltageOutputSwitchVoltageOutputSwitchCurrentJunctionTemperatureRangeLM1577LM2577

3󰀟5VsVINs40V0VsVSWITCHs60V

ISWITCHs3󰀟0A

b55󰀄CsTJsa150󰀄Cb40󰀄CsTJsa125󰀄C

260󰀄C150󰀄C2kV

SpecificationswithstandardtypefaceareforTJe25󰀄C󰀷andthoseinboldtypefaceapplyoverfullOperatingTemperatureRange󰀟Unlessotherwisespecified󰀷VINe5V󰀷andISWITCHe0󰀟Symbol

Parameter

Conditions

Typical

LM1577-12Limit(Notes3󰀷4)

LM2577-12Limit(Note5)

Units(Limits)

ElectricalCharacteristics󰁛LM1577-12󰀷LM2577-12

SYSTEMPARAMETERSCircuitofFigure1(Note6)VOUT

OutputVoltage

VINe5Vto10V

ILOADe100mAto800mA(Note3)

VINe3󰀟5Vto10VILOADe300mA

VINe5V

ILOADe100mAto800mAVINe5V󰀷ILOADe800mAVFEEDBACKe14V(SwitchOff)ISWITCHe2󰀟0A

VCOMPe2󰀟0V(MaxDutyCycle)

VUV

InputSupply

UndervoltageLockoutOscillatorFrequency

ISWITCHe100mA

12󰀟0

11󰀟60󰁋11󰀝4012󰀟40󰁋12󰀝60

20

50󰁋100

20

50󰁋100

80

50󰁋10050󰁋10011󰀟60󰁋11󰀝4012󰀟40󰁋12󰀝60

VV(min)V(max)mVmV(max)mVmV(max)%

DVOUTDVINDVOUTDLOADh

LineRegulationLoadRegulationEfficiency

DEVICEPARAMETERSIS

InputSupplyCurrent

7󰀟5

10󰀟0󰁋14󰀝0

25

50󰁋85

2󰀟90

2󰀟70󰁋2󰀝653󰀟10󰁋3󰀝15

MeasuredatSwitchPinISWITCHe100mAMeasuredatFeedbackPinVINe3󰀟5Vto40VVCOMPe1󰀟0VVINe3󰀟5Vto40V

52

48󰁋4256󰁋62

12

11󰀟76󰁋11󰀝6412󰀟24󰁋12󰀝36

48󰁋4256󰁋6211󰀟76󰁋11󰀝6412󰀟24󰁋12󰀝362󰀟70󰁋2󰀝653󰀟10󰁋3󰀝1550󰁋8510󰀟0󰁋14󰀝0

mAmA(max)mAmA(max)VV(min)V(max)kHzkHz(min)kHz(max)VV(min)V(max)mVkXmmhommho(min)mmho(max)V󰁋VV󰁋V(min)

fO

VREF

OutputReferenceVoltage

OutputReference

VoltageLineRegulatorFeedbackPinInputResistanceErrorAmp

TransconductanceErrorAmpVoltageGain

DVREFDVINRFBGM

79󰀟7

ICOMPeb30mAtoa30mAVCOMPe1󰀟0VVCOMPe1󰀟1Vto1󰀟9VRCOMPe1󰀟0MX(Note7)

2

370

225󰁋145515󰁋615

80

50󰁋25

50󰁋25225󰁋145515󰁋615

AVOL

ElectricalCharacteristics󰁛LM1577-12󰀷LM2577-12(Continued)

SpecificationswithstandardtypefaceareforTJe25󰀄C󰀷andthoseinboldtypefaceapplyoverfullOperatingTemperatureRange󰀟Unlessotherwisespecified󰀷VINe5V󰀷andISWITCHe0󰀟

Symbol

Parameter

Conditions

Typical

LM1577-12Limit(Notes3󰀷4)

LM2577-12Limit(Note5)

Units(Limits)

DEVICEPARAMETERS(Continued)

ErrorAmplifierOutputSwing

UpperLimit

VFEEDBACKe10󰀟0VLowerLimit

VFEEDBACKe15󰀟0V

ErrorAmplifierOutputCurrent

ISS

SoftStartCurrent

VFEEDBACKe10󰀟0Vto15󰀟0VVCOMPe1󰀟0VVFEEDBACKe10󰀟0VVCOMPe0VVCOMPe1󰀟5VISWITCHe100mA

2󰀟4

2󰀟2󰁋2󰀝0

0󰀟3

0󰀟40󰁋0󰀝55

g200

g130󰁋g90g300󰁋g400

g130󰁋g90g300󰁋g400

2󰀟2󰁋2󰀝00󰀟40󰁋0󰀝55

VV(min)VV(max)mAmA(min)mA(max)mAmA(min)mA(max)%%(min)A󰁋VmAmA(max)VV(max)AA(min)A(max)

5󰀟0

2󰀟5󰁋1󰀝57󰀟5󰁋9󰀝5

95

93󰁋90

12󰀟5

93󰁋902󰀟5󰁋1󰀝57󰀟5󰁋9󰀝5

DDISWITCHDVCOMPILVSAT

MaximumDutyCycleSwitch

TransconductanceSwitchLeakageCurrent

SwitchSaturationVoltageNPNSwitchCurrentLimit

VSWITCHe65V

VFEEDBACKe15V(SwitchOff)ISWITCHe2󰀟0A

VCOMPe2󰀟0V(MaxDutyCycle)

10

300󰁋600

0󰀟5

0󰀟7󰁋0󰀝9

4󰀟5

3󰀟7󰁋3󰀝05󰀟3󰁋6󰀝0

3󰀟7󰁋3󰀝05󰀟3󰁋6󰀝00󰀟7󰁋0󰀝9300󰁋600

3

SpecificationswithstandardtypefaceareforTJe25󰀄C󰀷andthoseinboldtypefaceapplyoverfullOperatingTemperatureRange󰀟Unlessotherwisespecified󰀷VINe5V󰀷andISWITCHe0󰀟Symbol

Parameter

Conditions

Typical

LM1577-15Limit(Notes3󰀷4)

LM2577-15Limit(Note5)

Units(Limits)

ElectricalCharacteristics󰁛LM1577-15󰀷LM2577-15

SYSTEMPARAMETERSCircuitofFigure2(Note6)VOUT

OutputVoltage

VINe5Vto12V

ILOADe100mAto600mA(Note3)

VINe3󰀟5Vto12VILOADe300mA

VINe5V

ILOADe100mAto600mAVINe5V󰀷ILOADe600mAVFEEDBACKe18󰀟0V(SwitchOff)ISWITCHe2󰀟0AVCOMPe2󰀟0V(MaxDutyCycle)

VUV

InputSupplyUndervoltageLockout

OscillatorFrequency

ISWITCHe100mA

15󰀟0

14󰀟50󰁋14󰀝2515󰀟50󰁋15󰀝75

20

50󰁋100

20

50󰁋100

80

50󰁋10050󰁋10014󰀟50󰁋14󰀝2515󰀟50󰁋15󰀝75

VV(min)V(max)mVmV(max)mVmV(max)%

DVOUTVINDVOUTDILOADh

LineRegulationLoadRegulationEfficiency

DEVICEPARAMETERSIS

InputSupplyCurrent

7󰀟5

10󰀟0󰁋14󰀝0

25

50󰁋85

2󰀟90

2󰀟70󰁋2󰀝653󰀟10󰁋3󰀝15

MeasuredatSwitchPinISWITCHe100mAMeasuredatFeedbackPinVINe3󰀟5Vto40VVCOMPe1󰀟0VVINe3󰀟5Vto40V

52

48󰁋4256󰁋62

15

14󰀟70󰁋14󰀝5515󰀟30󰁋15󰀝45

48󰁋4256󰁋6214󰀟70󰁋14󰀝5515󰀟30󰁋15󰀝452󰀟70󰁋2󰀝653󰀟10󰁋3󰀝1550󰁋8510󰀟0󰁋14󰀝0

mAmA(max)mAmA(max)VV(min)V(max)kHzkHz(min)kHz(max)VV(min)V(max)mVkXmmhommho(min)mmho(max)V󰁋VV󰁋V(min)

fO

VREF

OutputReferenceVoltage

OutputReference

VoltageLineRegulationFeedbackPinInputVoltageLineRegulatorErrorAmp

TransconductanceErrorAmpVoltageGain

DVREFDVINRFBGM

1012󰀟2

ICOMPeb30mAtoa30mAVCOMPe1󰀟0VVCOMPe1󰀟1Vto1󰀟9VRCOMPe1󰀟0MX(Note7)

300

170󰁋110420󰁋500

65

40󰁋20

40󰁋20170󰁋110420󰁋500

AVOL

4

ElectricalCharacteristics󰁛LM1577-15󰀷LM2577-15(Continued)

SpecificationswithstandardtypefaceareforTJe25󰀄C󰀷andthoseinboldtypefaceapplyoverfullOperatingTemperatureRange󰀟Unlessotherwisespecified󰀷VINe5V󰀷andISWITCHe0󰀟

Symbol

Parameter

Conditions

Typical

LM1577-15Limit(Notes3󰀷4)

LM2577-15Limit(Note5)

Units(Limits)

DEVICEPARAMETERS(Continued)

ErrorAmplifierOutputSwing

UpperLimit

VFEEDBACKe12󰀟0VLowerLimit

VFEEDBACKe18󰀟0V

ErrorAmp

OutputCurrent

ISS

SoftStartCurrent

VFEEDBACKe12󰀟0Vto18󰀟0VVCOMPe1󰀟0VVFEEDBACKe12󰀟0VVCOMPe0VVCOMPe1󰀟5VISWITCHe100mA

2󰀟4

2󰀟2󰁋2󰀝0

0󰀟3

0󰀟4󰁋0󰀝55

g200

g130󰁋g90g300󰁋g400

g130󰁋g90g300󰁋g400

2󰀟2󰁋2󰀝00󰀟40󰁋0󰀝55

VV(min)VV(max)mAmA(min)mA(max)mAmA(min)mA(max)%%(min)A󰁋VmA

5󰀟0

2󰀟5󰁋1󰀝57󰀟5󰁋9󰀝5

95

93󰁋90

12󰀟5

93󰁋902󰀟5󰁋1󰀝57󰀟5󰁋9󰀝5

DDISWITCHDVCOMPIL

MaximumDutyCycle

Switch

TransconductanceSwitchLeakageCurrent

SwitchSaturationVoltageNPNSwitchCurrentLimit

VSWITCHe65V

VFEEDBACKe18󰀟0V(SwitchOff)ISWITCHe2󰀟0AVCOMPe2󰀟0V(MaxDutyCycle)VCOMPe2󰀟0V

10

300󰁋600

0󰀟5

0󰀟7󰁋0󰀝9

4󰀟3

3󰀟7󰁋3󰀝05󰀟3󰁋6󰀝0

3󰀟7󰁋3󰀝05󰀟3󰁋6󰀝00󰀟7󰁋0󰀝9300󰁋600

mA(max)

VV(max)AA(min)A(max)

VSAT

5

ElectricalCharacteristics󰁛LM1577-ADJ󰀷LM2577-ADJ

SpecificationswithstandardtypefaceareforTJe25󰀄C󰀷andthoseinboldtypefaceapplyoverfullOperatingTemperatureRange󰀟Unlessotherwisespecified󰀷VINe5V󰀷VFEEDBACKeVREF󰀷andISWITCHe0󰀟Symbol

Parameter

Conditions

Typical

LM1577-ADJ

Limit(Notes3󰀷4)

LM2577-ADJ

Limit(Note5)

Units(Limits)

SYSTEMPARAMETERSCircuitofFigure3(Note6)VOUT

OutputVoltage

VINe5Vto10V

ILOADe100mAto800mA(Note3)

VINe3󰀟5Vto10VILOADe300mA

VINe5V

ILOADe100mAto800mAVINe5V󰀷ILOADe800mAVFEEDBACKe1󰀟5V(SwitchOff)ISWITCHe2󰀟0A

VCOMPe2󰀟0V(MaxDutyCycle)

VUV

InputSupply

UndervoltageLockoutOscillatorFrequency

ISWITCHe100mA

12󰀟0

11󰀟60󰁋11󰀝4012󰀟40󰁋12󰀝60

20

50󰁋100

20

50󰁋100

80

50󰁋10050󰁋10011󰀟60󰁋11󰀝4012󰀟40󰁋12󰀝60

VV(min)V(max)mVmV(max)mVmV(max)%

DVOUT󰁋DVINDVOUT󰁋DILOADh

LineRegulationLoadRegulationEfficiency

DEVICEPARAMETERSIS

InputSupplyCurrent

7󰀟5

10󰀟0󰁋14󰀝0

25

50󰁋85

2󰀟90

2󰀟70󰁋2󰀝653󰀟10󰁋3󰀝15

MeasuredatSwitchPinISWITCHe100mAMeasuredatFeedbackPinVINe3󰀟5Vto40VVCOMPe1󰀟0VVINe3󰀟5Vto40VVCOMPe1󰀟0V

ICOMPeb30mAtoa30mAVCOMPe1󰀟0V

VCOMPe1󰀟1Vto1󰀟9VRCOMPe1󰀟0MX(Note7)UpperLimit

VFEEDBACKe1󰀟0VLowerLimit

VFEEDBACKe1󰀟5V

52

48󰁋4256󰁋62

1󰀟230

1󰀟214󰁋1󰀝2061󰀟246󰁋1󰀝254

48󰁋4256󰁋621󰀟214󰁋1󰀝2061󰀟246󰁋1󰀝2542󰀟70󰁋2󰀝653󰀟10󰁋3󰀝1550󰁋8510󰀟0󰁋14󰀝0

mAmA(max)mAmA(max)VV(min)V(max)kHzkHz(min)kHz(max)VV(min)V(max)mVnAnA(max)mmhommho(min)mmho(max)V󰁋VV󰁋V(min)VV(min)VV(max)

fO

VREF

ReferenceVoltage

ReferenceVoltageLineRegulationErrorAmp

InputBiasCurrentErrorAmp

TransconductanceErrorAmpVoltageGainErrorAmplifierOutputSwing

DVREF󰁋DVINIBGM

0󰀟5100

300󰁋800

3700

2400󰁋16004800󰁋5800

800

500󰁋250

2󰀟4

2󰀟2󰁋2󰀝0

0󰀟3

0󰀟40󰁋0󰀝55

0󰀟40󰁋0󰀝552󰀟2󰁋2󰀝0500󰁋2502400󰁋16004800󰁋5800300󰁋800

AVOL

6

ElectricalCharacteristics󰁛LM1577-ADJ󰀷LM2577-ADJ(Continued)

SpecificationswithstandardtypefaceareforTJe25󰀄C󰀷andthoseinboldtypefaceapplyoverfullOperatingTemperatureRange󰀟Unlessotherwisespecified󰀷VINe5V󰀷VFEEDBACKeVREF󰀷andISWITCHe0󰀟Symbol

Parameter

Conditions

Typical

LM1577-ADJ

Limit(Notes3󰀷4)

LM2577-ADJ

Limit(Note5)

Units(Limits)

DEVICEPARAMETERS(Continued)

ErrorAmp

OutputCurrent

ISS

SoftStartCurrent

VFEEDBACKe1󰀟0Vto1󰀟5VVCOMPe1󰀟0VVFEEDBACKe1󰀟0VVCOMPe0VVCOMPe1󰀟5VISWITCHe100mA

g200

g130󰁋g90g300󰁋g400

g130󰁋g90g300󰁋g400

mAmA(min)mA(max)mAmA(min)mA(max)%%(min)A󰁋VmAmA(max)VV(max)AA(min)A(max)

5󰀟0

2󰀟5󰁋1󰀝57󰀟5󰁋9󰀝5

95

93󰁋90

12󰀟5

93󰁋902󰀟5󰁋1󰀝57󰀟5󰁋9󰀝5

D

DISWITCH󰁋DVCOMPILVSAT

MaximumDutyCycleSwitch

TransconductanceSwitchLeakageCurrent

SwitchSaturationVoltageNPNSwitchCurrentLimit

VSWITCHe65V

VFEEDBACKe1󰀟5V(SwitchOff)ISWITCHe2󰀟0A

VCOMPe2󰀟0V(MaxDutyCycle)VCOMPe2󰀟0V

10

300󰁋600

0󰀟5

0󰀟7󰁋0󰀝9

4󰀟3

3󰀟7󰁋3󰀝05󰀟3󰁋6󰀝0

3󰀟7󰁋3󰀝05󰀟3󰁋6󰀝00󰀟7󰁋0󰀝9300󰁋600

THERMALPARAMETERS(AllVersions)iJAiJCiJAiJCiJAiJAiJA

ThermalResistance

KPackage󰀷JunctiontoAmbientKPackage󰀷JunctiontoCaseTPackage󰀷JunctiontoAmbientTPackage󰀷JunctiontoCaseNPackage󰀷JunctiontoAmbient(Note8)MPackage󰀷JunctiontoAmbient(Note8)SPackage󰀷JunctiontoAmbient(Note9)

351󰀟56528510037

󰀄C󰁋W

Note1󰀌AbsoluteMaximumRatingsindicatelimitsbeyondwhichdamagetothedevicemayoccur󰀟Operatingratingsindicateconditionsthedeviceisintendedtobefunctional󰀷butdeviceparameterspecificationsmaynotbeguaranteedundertheseconditions󰀟Forguaranteedspecificationsandtestconditions󰀷seetheElectricalCharacteristics󰀟

Note2󰀌DuetotimingconsiderationsoftheLM1577󰁋LM2577currentlimitcircuit󰀷outputcurrentcannotbeinternallylimitedwhentheLM1577󰁋LM2577isusedasastep-upregulator󰀟Topreventdamagetotheswitch󰀷itscurrentmustbeexternallylimitedto6󰀟0A󰀟However󰀷outputcurrentisinternallylimitedwhentheLM1577󰁋LM2577isusedasaflybackorforwardconverterregulatorinaccordancetotheApplicationHints󰀟

Note3󰀌Alllimitsguaranteedatroomtemperature(standardtypeface)andattemperatureextremes(boldfacetype)󰀟AlllimitsareusedtocalculateOutgoingQualityLevel󰀷andare100%productiontested󰀟

Note4󰀌AmilitaryRETSelectricaltestspecificationisavailableonrequest󰀟Atthetimeofprinting󰀷theLM1577K-12󰁋883󰀷LM1577K-15󰁋883󰀷andLM1577K-ADJ󰁋883RETSspecificationscompliedfullywiththeboldfacelimitsinthesecolumns󰀟TheLM1577K-12󰁋883󰀷LM1577K-15󰁋883󰀷andLM1577K-ADJ󰁋883mayalsobeprocuredtoStandardMilitaryDrawingspecifications󰀟

Note5󰀌Alllimitsguaranteedatroomtemperature(standardtypeface)andattemperatureextremes(boldfacetype)󰀟Allroomtemperaturelimitsare100%productiontested󰀟AlllimitsattemperatureextremesareguaranteedviacorrelationusingstandardStatisticalQualityControl(SQC)methods󰀟

Note6󰀌Externalcomponentssuchasthediode󰀷inductor󰀷inputandoutputcapacitorscanaffectswitchingregulatorperformance󰀟WhentheLM1577󰁋LM2577isusedasshownintheTestCircuit󰀷systemperformancewillbeasspecifiedbythesystemparameters󰀟

Note7󰀌A1󰀟0MXresistorisconnectedtothecompensationpin(whichistheerroramplifier’soutput)toensureaccuracyinmeasuringAVOL󰀟Inactualapplications󰀷thispin’sloadresistanceshouldbet10MX󰀷resultinginAVOLthatistypicallytwicetheguaranteedminimumlimit󰀟

Note8󰀌Junctiontoambientthermalresistancewithapproximately1squareinchofpcboardcoppersurroundingtheleads󰀟Additionalcopperareawilllowerthermalresistancefurther󰀟Seethermalmodelin‘‘SwitchersMadeSimple’’software󰀟

Note9󰀌IftheTO-263packageisused󰀷thethermalresistancecanbereducedbyincreasingthePCboardcopperareathermallyconnectedtothepackage󰀟Using0󰀟5squareinchesofcopperarea󰀷iJAis50󰀄C󰁋W󰀥with1squareinchofcopperarea󰀷iJAis37󰀄C󰁋W󰀥andwith1󰀟6ormoresquareinchesofcopperarea󰀷iJAis32󰀄C󰁋W󰀟

7

TypicalPerformanceCharacteristics

ReferenceVoltagevsTemperature

ReferenceVoltagevsTemperature

ReferenceVoltagevsTemperature

DReferenceVoltagevsSupplyVoltageDReferenceVoltagevsSupplyVoltageDReferenceVoltagevsSupplyVoltage

ErrorAmpTransconductancevsTemperatureErrorAmpTransconductancevsTemperatureErrorAmpTransconductancevsTemperature

ErrorAmpVoltageGainvsTemperatureErrorAmpVoltageGainvsTemperatureErrorAmpVoltageGainvsTemperature

TL󰁋H󰁋11468–2

8

TypicalPerformanceCharacteristics

QuiescentCurrentvsTemperature

(Continued)

CurrentLimitvsTemperature

QuiescentCurrentvsSwitchCurrent

CurrentLimitResponseTimevsOverdriveSwitchSaturationVoltagevsSwitchCurrentSwitchTransconductancevsTemperature

FeedbackPinBias

CurrentvsTemperatureOscillatorFrequencyvsTemperature

TL󰁋H󰁋11468–3

MaximumPowerDissipation(TO-263)(SeeNote9)

TL󰁋H󰁋11468–31

9

ConnectionDiagrams

StraightLeads5-LeadTO-220(T)

TL󰁋H󰁋11468–4TopView

OrderNumberLM2577T-12󰀷LM2577T-15󰀷

orLM2577T-ADJ

SeeNSPackageNumberT05A

16-LeadDIP(N)󰀁NointernalConnection

TopView

TL󰁋H󰁋11468–6

OrderNumberLM2577N-12󰀷LM2577N-15󰀷

orLM2577N-ADJ

SeeNSPackageNumberN16A

TO-263(S)

5-LeadSurface-MountPackage

TL󰁋H󰁋11468-32

TopView

Bent󰀷StaggeredLeads5-LeadTO-220(T)

TL󰁋H󰁋11468–5

TopView

OrderNumberLM2577T-12FlowLB03󰀷LM2577T-15

FlowLB03󰀷orLM2577T-ADJFlowLB03

SeeNSPackageNumberT05D

24-LeadSurfaceMount(M)

󰀁NointernalConnection

TopView

TL󰁋H󰁋11468–7

OrderNumberLM2577M-12󰀷LM2577M-15󰀷

orLM2577M-ADJ

SeeNSPackageNumberM24B

TestCircuits

LM1577-12󰀷LM2577-12

TL󰁋H󰁋11468–30

Le415-0930(AIE)DeanymanufacturerCOUTeSpragueType673D

Electrolytic680mF󰀷20VNote󰀌PinnumbersshownareforTO-220(T)package

FIGURE1󰀟CircuitUsedtoSpecifySystemParametersfor12VVersions

LM1577-15󰀷LM2577-15

TL󰁋H󰁋11468–26

Le415-0930(AIE)DeanymanufacturerCOUTeSpragueType673D

Electrolytic680mF󰀷20VNote󰀌PinnumbersshownareforTO-220(T)package

FIGURE2󰀟CircuitUsedtoSpecifySystemParametersfor15VVersions

LM1577-ADJ󰀷LM2577-ADJ

Note󰀌PinnumbersshownareforTO-220(T)package

TL󰁋H󰁋11468–9

Le415-0930(AIE)DeanymanufacturerCOUTeSpragueType673D

Electrolytic680mF󰀷20VR1e48󰀟7kinserieswith511X(1%)R2e5󰀟62k(1%)

FIGURE3󰀟CircuitUsedtoSpecifySystemParametersforADJVersions

11

ApplicationHints

Note󰀌PinnumbersshownareforTO-220(T)package󰀁ResistorsareinternaltoLM1577󰁋LM2577for12Vand15Vversions󰀟

TL󰁋H󰁋11468–10

FIGURE4󰀟LM1577󰁋LM2577BlockDiagramandBoostRegulatorApplication

STEP-UP(BOOST)REGULATOR

Whentheswitchturnsoff󰀷thelowerendoftheinductorfliesaboveVIN󰀷dischargingitscurrentthroughdiode(D)intotheoutputcapacitor(COUT)atarateof(VOUTbVIN)󰁋L󰀟Thus󰀷energystoredintheinductorduringtheswitchontimeistransferredtotheoutputduringtheswitchofftime󰀟Theout-putvoltageiscontrolledbytheamountofenergytrans-ferredwhich󰀷inturn󰀷iscontrolledbymodulatingthepeakinductorcurrent󰀟Thisisdonebyfeedingbackaportionoftheoutputvoltagetotheerroramp󰀷whichamplifiesthedif-ferencebetweenthefeedbackvoltageanda1󰀟230Vrefer-ence󰀟Theerrorampoutputvoltageiscomparedtoavolt-ageproportionaltotheswitchcurrent(i󰀟e󰀟󰀷inductorcurrentduringtheswitchontime)󰀟

Figure4showstheLM1577-ADJ󰁋LM2577-ADJusedasaStep-UpRegulator󰀟Thisisaswitchingregulatorusedforproducinganoutputvoltagegreaterthantheinputsupplyvoltage󰀟TheLM1577-12󰁋LM2577-12andLM1577-15󰁋LM2577-15canalsobeusedforstep-upregulatorswith12Vor15Voutputs(respectively)󰀷bytyingthefeedbackpindirectlytotheregulatoroutput󰀟

Abasicexplanationofhowitworksisasfollows󰀟TheLM1577󰁋LM2577turnsitsoutputswitchonandoffatafre-quencyof52kHz󰀷andthiscreatesenergyintheinductor(L)󰀟WhentheNPNswitchturnson󰀷theinductorcurrentchargesupatarateofVIN󰁋L󰀷storingcurrentintheinductor󰀟

12

ApplicationHints(Continued)

Thecomparatorterminatestheswitchontimewhenthetwovoltagesareequal󰀷therebycontrollingthepeakswitchcur-renttomaintainaconstantoutputvoltage󰀟

VoltageandcurrentwaveformsforthiscircuitareshowninFigure5󰀷andformulasforcalculatingthemaregiveninFig-ure6󰀟

Beforeproceedinganyfurther󰀷determineiftheLM1577󰁋LM2577canprovidethesevaluesofVOUTandILOAD(max)whenoperatingwiththeminimumvalueofVIN󰀟TheupperlimitsforVOUTandILOAD(max)aregivenbythefollowingequations󰀟

VOUTs60V

andVOUTs10cVIN(min)

2󰀟1AcVIN(min)

ILOAD(max)s

VOUTTheselimitsmustbegreaterthanorequaltothevaluesspecifiedinthisapplication󰀟1󰀟InductorSelection(L)A󰀟VoltageOptions󰀌1󰀟For12Vor15Voutput

FromFigure7a(for12Voutput)orFigure7b(for15Voutput)󰀷identifyinductorcodeforregionindicatedbyVIN(min)andILOAD(max)󰀟TheshadedregionindicatesconditionsforwhichtheLM1577󰁋LM2577outputswitchwouldbeoperatingbeyonditsswitchcurrentrating󰀟TheminimumoperatingvoltagefortheLM1577󰁋LM2577is3󰀟5V󰀟

Fromhere󰀷proceedtostepC󰀟2󰀟ForAdjustableversion

Preliminarycalculations󰀌

Theinductorselectionisbasedonthecalculationofthefollowingthreeparameters󰀌

D(max)󰀷themaximumswitchdutycycle(0sDs0󰀟9)󰀌VOUTaVFbVIN(min)

D(max)e

VOUTaVFb0󰀟6V

whereVFe0󰀟5VforSchottkydiodesand0󰀟8Vforfastrecoverydiodes(typically)󰀥

TL󰁋H󰁋11468–11

FIGURE5󰀟Step-UpRegulatorWaveforms

DutyCycleAverageInductorCurrentInductorCurrentRipplePeakInductorCurrentPeakSwitchCurrentSwitchVoltageWhenOffDiodeReverseVoltageAverageDiodeCurrentPeakDiodeCurrent

PowerDissipationofLM1577󰁋2577

D

bVINVVOUTaVFbVIN

󰀇OUT

VOUTaVFbVSATVOUT

IIND(AVE)DIINDIIND(PK)ISW(PK)VSW(OFF)

VRID(AVE)ID(PK)PD

0󰀟25X

ILOAD

1bD

VINbVSATD

L52󰀷000ILOAD(max)DI

aIND

1bD(max)2ILOAD(max)DI

aIND

b1D(max)2

VOUTaVFVOUTbVSAT

ILOAD

ILOADDI

aIND

1bD(max)2

󰀣ILOAD2ILOADDVIN

Da

1bD50(1bD)

JVFeForwardBiasedDiodeVoltage

ILOADeOutputLoadCurrent

FIGURE6󰀟Step-UpRegulatorFormulas

STEP-UPREGULATORDESIGNPROCEDURE

ThefollowingdesignprocedurecanbeusedtoselecttheappropriateexternalcomponentsforthecircuitinFigure4󰀷basedonthesesystemrequirements󰀟Given󰀌

VIN(min)eMinimuminputsupplyvoltageVOUTeRegulatedoutputvoltage

ILOAD(max)eMaximumoutputloadcurrent

E󰀣T󰀷theproductofvoltsctimethatchargestheinductor󰀌

D(max)(VIN(min)b0󰀟6V)106

(V󰀣ms)E󰀣Te

52󰀷000Hz

IIND󰀷DC󰀷theaverageinductorcurrentunderfullload󰀥

1󰀟05cILOAD(max)

IIND󰀷DCe

1bD(max)

B󰀟IdentifyInductorValue󰀌1󰀟FromFigure7c󰀷identifytheinductorcodefortheregionindicatedbytheintersectionofE󰀣TandIIND󰀷DC󰀟Thiscodegivestheinductorvalueinmicrohenries󰀟TheLorHprefixsignifieswhethertheinductorisratedforamaximumE󰀣Tof90V󰀣ms(L)or250V󰀣ms(H)󰀟

2󰀟IfDk0󰀟85󰀷goontostepC󰀟IfDt0󰀟85󰀷thencalculatetheminimuminductanceneededtoensuretheswitchingregulator’sstability󰀌

6󰀟4(VIN(min)b0󰀟6V)(2D(max)b1)

(mH)LMINe

1bD(max)

IfLMINissmallerthantheinductorvaluefoundinstepB1󰀷goontostepC󰀟Otherwise󰀷theinductorvaluefoundinstepB1istoolow󰀥anappropriateinductorcodeshouldbeob-tainedfromthegraphasfollows󰀌

1󰀟FindthelowestvalueinductorthatisgreaterthanLMIN󰀟2󰀟FindwhereE󰀣Tintersectsthisinductorvaluetodeter-mineifithasanLorHprefix󰀟IfE󰀣TintersectsboththeLandHregions󰀷selecttheinductorwithanHprefix󰀟

13

ApplicationHints(Continued)

TL󰁋H󰁋11468–27TL󰁋H󰁋11468–28

FIGURE7a󰀟LM2577-12InductorSelectionGuideFIGURE7b󰀟LM2577-15InductorSelectionGuide

TL󰁋H󰁋11468–12

FIGURE7c󰀟LM1577-ADJ󰁋LM2577-ADJInductorSelectionGraph

Note󰀌

Thesechartsassumethattheinductorripplecurrentinductorisapproximately20%to30%oftheaverageinductorcurrent(whentheregulatorisunderfullload)󰀟Greaterripplecurrentcauseshigherpeakswitchcurrentsandgreateroutputripplevoltage󰀥lowerripplecurrentisachievedwithlarger-valueinductors󰀟Thefactorof20to30%ischosenasaconvenientbalancebetweenthetwoextremes󰀟

14

ApplicationHints(Continued)

C󰀟SelectaninductorfromthetableofFigure8whichcross-referencestheinductorcodestothepartnumbersofthreedifferentmanufacturers󰀟Completespecificationsfortheseinductorsareavailablefromtherespectivemanufacturers󰀟Theinductorslistedinthistablehavethefollowingcharac-teristics󰀌

A󰀟First󰀷calculatethemaximumvalueforRC󰀟RCs

750cILOAD(max)cVOUT2

VIN(min)2

Selectaresistorlessthanorequaltothisvalue󰀷anditshouldalsobenogreaterthan3kX󰀟

B󰀟CalculatetheminimumvalueforCOUTusingthefollowingtwoequations󰀟

COUTt

and

VIN(min)cRCc(VIN(min)a(3󰀟74c105cL))

487󰀷800cVOUT3

Thelargerofthesetwovaluesistheminimumvaluethatensuresstability󰀟

C󰀟CalculatetheminimumvalueofCC󰀟COUTt

58󰀟5cVOUT2cCOUT

RC2cVIN(min)

Thecompensationcapacitorisalsopartofthesoftstartcircuitry󰀟Whenpowertotheregulatoristurnedon󰀷theswitchdutycycleisallowedtoriseataratecontrolledbythiscapacitor(withnocontrolonthedutycycle󰀷itwouldimmediatelyriseto90%󰀷drawinghugecurrentsfromtheinputpowersupply)󰀟Inordertooperateproperly󰀷thesoftstartcircuitrequiresCCt0󰀟22mF󰀟

Thevalueoftheoutputfiltercapacitorisnormallylargeenoughtorequiretheuseofaluminumelectrolyticcapaci-tors󰀟Figure9listsseveraldifferenttypesthatarerecom-mendedforswitchingregulators󰀷andthefollowingparame-tersareusedtoselectthepropercapacitor󰀟

CCt

0󰀟19cLcRCcILOAD(max)

VIN(min)cVOUT

AIE󰀌ferrite󰀷pot-coreinductors󰀥Benefitsofthistypearelowelectro-magneticinterference(EMI)󰀷smallphysicalsize󰀷andverylowpowerdissipation(coreloss)󰀟Becare-fulnottooperatetheseinductorstoofarbeyondtheirmaximumratingsforE󰀣Tandpeakcurrent󰀷asthiswillsaturatethecore󰀟

Pulse󰀌powderediron󰀷toroidcoreinductors󰀥BenefitsarelowEMIandabilitytowithstandE󰀣Tandpeakcurrentaboveratedvaluebetterthanferritecores󰀟

Renco󰀌ferrite󰀷bobbin-coreinductors󰀥BenefitsarelowcostandbestabilitytowithstandE󰀣Tandpeakcurrentaboveratedvalue󰀟Beawarethattheseinductorsgener-atemoreEMIthantheothertypes󰀷andthismayinterferewithsignalssensitivetonoise󰀟InductorCodeL47L68L100L150L220L330L470L680H150H220H330H470H680H1000H1500H2200

Manufacturer’sPartNumberSchott67126980671269906712700067127010671270206712703067127040671270506712706067127070671270806712709067127100671271106712712067127130

PulsePE-53112PE-92114PE-92108PE-53113PE-52626PE-52627PE-53114PE-52629PE-53115PE-53116PE-53117PE-53118PE-53119PE-53120PE-53121PE-53122

RencoRL2442RL2443RL2444RL1954RL1953RL1952RL1951RL1950RL2445RL2446RL2447RL1961RL1960RL1959RL1958RL2448

SchottCorp󰀟󰀷(612)475-1173

1000ParkersLakeRd󰀟󰀷Wayzata󰀷MN55391PulseEngineering󰀷(619)268-2400P󰀟O󰀟Box12235󰀷SanDiego󰀷CA92112RencoElectronicsInc󰀟󰀷(516)586-556660JeffrynBlvd󰀟East󰀷DeerPark󰀷NY11729

FIGURE8󰀟TableofStandardizedInductorsand

Manufacturer’sPartNumbers

2󰀟CompensationNetwork(RC󰀷CC)andOutputCapaci-tor(COUT)Selection

RCandCCformapole-zerocompensationnetworkthatstabilizestheregulator󰀟ThevaluesofRCandCCaremainlydependantontheregulatorvoltagegain󰀷ILOAD(max)󰀷LandCOUT󰀟ThefollowingprocedurecalculatesvaluesforRC󰀷CC󰀷andCOUTthatensureregulatorstability󰀟Beawarethatthisproceduredoesn’tnecessarilyresultinRCandCCthatprovideoptimumcompensation󰀟Inordertoguaranteeopti-mumcompensation󰀷oneofthestandardproceduresfortestingloopstabilitymustbeused󰀷suchasmeasuringVOUTtransientresponsewhenpulsingILOAD(seeFigure13)󰀟

WorkingVoltage(WVDC)󰀌Chooseacapacitorwithawork-ingvoltageatleast20%higherthantheregulatoroutputvoltage󰀟

RippleCurrent󰀌ThisisthemaximumRMSvalueofcurrentthatchargesthecapacitorduringeachswitchingcycle󰀟Forstep-upandflybackregulators󰀷theformulaforripplecurrentis

ILOAD(max)cD(max)

IRIPPLE(RMS)e

1bD(max)

Chooseacapacitorthatisratedatleast50%higherthanthisvalueat52kHz󰀟

EquivalentSeriesResistance(ESR)󰀌Thisistheprimarycauseofoutputripplevoltage󰀷anditalsoaffectsthevaluesofRCandCCneededtostabilizetheregulator󰀟Asaresult󰀷theprecedingcalculationsforCCandRCareonlyvalidifESRdoesn’texceedthemaximumvaluespecifiedbythefollowingequations󰀟

0󰀟01cVOUT8󰀟7c(10)b3cVIN

ESRsands

IRIPPLE(P-P)ILOAD(max)

where

1󰀟15cILOAD(max)

IRIPPLE(P-P)e

1bD(max)

SelectacapacitorwithESR󰀷at52kHz󰀷thatislessthanorequaltothelowervaluecalculated󰀟Mostelectrolyticcapac-itorsspecifyESRat120Hzwhichis15%to30%higherthanat52kHz󰀟Also󰀷beawarethatESRincreasesbyafactorof2whenoperatingatb20󰀄C󰀟

15

ApplicationHints(Continued)

Ingeneral󰀷lowvaluesofESRareachievedbyusinglargevaluecapacitors(Ct470mF)󰀷andcapacitorswithhighWVDC󰀷orbyparallelingsmaller-valuecapacitors󰀟3󰀟OutputVoltageSelection(R1andR2)

ThissectionisforapplicationsusingtheLM1577-ADJ󰁋LM2577-ADJ󰀟SkipthissectioniftheLM1577-12󰁋LM2577-12orLM1577-15󰁋LM2577-15isbeingused󰀟

WiththeLM1577-ADJ󰁋LM2577-ADJ󰀷theoutputvoltageisgivenby

VOUTe1󰀟23V(1aR1󰁋R2)ResistorsR1andR2dividetheoutputdownsoitcanbecomparedwiththeLM1577-ADJ󰁋LM2577-ADJinternal1󰀟23Vreference󰀟ForagivendesiredoutputvoltageVOUT󰀷selectR1andR2sothat

R1V

eOUTb1R21󰀟23V

4󰀟InputCapacitorSelection(CIN)

Theswitchingactioninthestep-upregulatorcausesatrian-gularripplecurrenttobedrawnfromthesupplysource󰀟Thisinturncausesnoisetoappearonthesupplyvoltage󰀟ForproperoperationoftheLM1577󰀷theinputvoltageshouldbedecoupled󰀟BypassingtheInputVoltagepindirectlytoCornellDublier󰁚Types239󰀷250󰀷251󰀷UFT󰀷300󰀷

or350

P󰀟O󰀟Box128󰀷Pickens󰀷SC29671(803)878-6311

Nichicon󰁚TypesPF󰀷PX󰀷orPZ

927EastParkway󰀷Schaumburg󰀷IL60173(708)843-7500Sprague󰁚Types672D󰀷673D󰀷or674D

Box1󰀷SpragueRoad󰀷Lansing󰀷NC28643(919)384-2551

UnitedChemi-Con󰁚TypesLX󰀷SXF󰀷orSXJ

9801WestHigginsRoad󰀷Rosemont󰀷IL60018(708)696-2000

FIGURE9󰀟AluminumElectrolyticCapacitorsRecommendedforSwitchingRegulators

groundwithagoodquality󰀷lowESR󰀷0󰀟1mFcapacitor(leadsasshortaspossible)isnormallysufficient󰀟

IftheLM1577islocatedfarfromthesupplysourcefiltercapacitors󰀷anadditionallargeelectrolyticcapacitor(e󰀟g󰀟47mF)isoftenrequired󰀟5󰀟DiodeSelection(D)

Theswitchingdiodeusedintheboostregulatormustwith-standareversevoltageequaltothecircuitoutputvoltage󰀷andmustconductthepeakoutputcurrentoftheLM2577󰀟Asuitablediodemusthaveaminimumreversebreakdownvoltagegreaterthanthecircuitoutputvoltage󰀷andshouldberatedforaverageandpeakcurrentgreaterthanILOAD(max)andID(PK)󰀟Schottkybarrierdiodesareoftenfa-voredforuseinswitchingregulators󰀟Theirlowforwardvolt-agedropallowshigherregulatorefficiencythanifa(lessexpensive)fastrecoverydiodewasused󰀟SeeFigure10forrecommendedpartnumbersandvoltageratingsof1Aand3Adiodes󰀟VOUT(max)20V

Schottky1A1N5817MBR120P1N5818MBR130P11DQ031N5819MBR140P11DQ04MBR15011DQ05

3A1N5820MBR320P1N5821MBR330P31DQ031N5822MBR340P31DQ04MBR35031DQ05

1N4933MUR1051N4934HER102MUR11010DL1

FIGURE10󰀟DiodeSelectionChart

MR85130DL1MR831HER302

FastRecovery1A

3A

30V

40V

50V

100V

16

ApplicationHints(Continued)

BOOSTREGULATORCIRCUITEXAMPLE

Byaddingafewexternalcomponents(asshowninFigure11)󰀷theLM2577canbeusedtoproducearegulatedoutputvoltagethatisgreaterthantheappliedinputvoltage󰀟Typi-calperformanceofthisregulatorisshowninFigures12and13󰀟TheswitchingwaveformsobservedduringtheoperationofthiscircuitareshowninFigure14󰀟

TL󰁋H󰁋11468–13

Note󰀌PinnumbersshownareforTO-220(T)package󰀟

FIGURE11󰀟Step-upRegulatorDelivers12Vfroma5VInput

TL󰁋H󰁋11468–14

FIGURE12󰀟LineRegulation(Typical)ofStep-UpRegulatorofFigure11TL󰁋H󰁋11468–16

TL󰁋H󰁋11468–15

FIGURE13󰀟LoadTransientResponseofStep-Up

RegulatorofFigure11A󰀌OutputVoltageChange󰀷100mV󰁋div󰀟(AC-coupled)B󰀌Loadcurrent󰀷0󰀟2A󰁋divHorizontal󰀌5ms󰁋div

FIGURE14󰀟SwitchingWaveformsofStep-Up

RegulatorofFigure11A󰀌Switchpinvoltage󰀷10V󰁋divB󰀌Switchpincurrent󰀷2A󰁋divC󰀌Inductorcurrent󰀷2A󰁋div

D󰀌Outputripplevoltage󰀷100mV󰁋div(AC-coupled)Horizontal󰀌5ms󰁋div

17

ApplicationHints(Continued)

FLYBACKREGULATOR

AFlybackregulatorcanproducesingleormultipleoutputvoltagesthatarelowerorgreaterthantheinputsupplyvolt-age󰀟Figure15showstheLM1577󰁋LM2577usedasafly-backregulatorwithpositiveandnegativeregulatedoutputs󰀟Itsoperationissimilartoastep-upregulator󰀷excepttheoutputswitchcontolstheprimarycurrentofaflybacktrans-former󰀟Notethattheprimaryandsecondarywindingsareoutofphase󰀷sonocurrentflowsthroughsecondarywhencurrentflowsthroughtheprimary󰀟Thisallowstheprimarytochargeupthetransformercorewhentheswitchison󰀟Whentheswitchturnsoff󰀷thecoredischargesbysendingcurrentthroughthesecondary󰀷andthisproducesvoltageattheoutputs󰀟Theoutputvoltagesarecontrolledbyadjustingthepeakprimarycurrent󰀷asdescribedinthestep-upregulatorsection󰀟

VoltageandcurrentwaveformsforthiscircuitareshowninFigure16󰀷andformulasforcalculatingthemaregiveninFigure17󰀟

FLYBACKREGULATORDESIGNPROCEDURE

1󰀟TransformerSelection

Afamilyofstandardizedflybacktransformersisavailableforcreatingflybackregulatorsthatproducedualoutputvolt-ages󰀷fromg10Vtog15V󰀷asshowninFigure15󰀟Figure18liststhesetransformerswiththeinputvoltage󰀷outputvoltagesandmaximumloadcurrenttheyaredesignedfor󰀟2󰀟CompensationNetwork(CC󰀷RC)andOutputCapacitor(COUT)Selection

AsexplainedintheStep-UpRegulatorDesignProcedure󰀷CC󰀷RCandCOUTmustbeselectedasagroup󰀟Thefollow-ingprocedureisforadualoutputflybackregulatorwithequalturnsratiosforeachsecondary(i󰀟e󰀟󰀷bothoutputvolt-ageshavethesamemagnitude)󰀟TheequationscanbeusedforasingleoutputregulatorbychangingRILOAD(max)toILOAD(max)inthefollowingequations󰀟

A󰀟First󰀷calculatethemaximumvalueforRC󰀟

750cRILOAD(max)c(15VaVIN(min)N)2

RCs

VIN(min)2

TL󰁋H󰁋11468–17

WhereRILOAD(max)isthesumoftheloadcurrent(magni-tude)requiredfrombothoutputs󰀟Selectaresistorlessthanorequaltothisvalue󰀷andnogreaterthan3kX󰀟

B󰀟CalculatetheminimumvalueforRCOUT(sumofCOUTatbothoutputs)usingthefollowingtwoequations󰀟

COUTt

and

VIN(min)cRCcN2c(VIN(min)a(3󰀟74c105cLP))

487󰀷800c(15V)2c(15VaVIN(min)cN)

Thelargerofthesetwovaluesmustbeusedtoensureregu-latorstability󰀟COUTt

0󰀟19cRCcLPcRILOAD(max)

15VcVIN(min)

FIGURE16󰀟FlybackRegulatorWaveforms

TL󰁋H󰁋11468–18

T1ePulseEngineering󰀷PE-65300D1󰀷D2e1N5821

FIGURE15󰀟LM1577-ADJ󰁋LM2577-ADJFlybackRegulatorwithgOutputs

18

ApplicationHints(Continued)

DutyCycle

D

VOUTaVF

󰀇

N(VINbVSAT)aVOUTaVF

VOUT

N(VIN)aVOUT

D(VINbVSAT)LPc52󰀷000NRILOADDIcaPK

bh1D2VOUTaVF

VINa

NVOUTaN(VINbVSAT)

ILOADILOADDI

aIND

1bD2

󰀇6A

N

PrimaryCurrentVariationPeakPrimaryCurrentSwitchVoltagewhenOffDiodeReverseVoltageAverageDiodeCurrentPeakDiodeCurrentShortCircuitDiodeCurrentPowerDissipationofLM1577󰁋LM2577

DIPIP(PK)VSW(OFF)

VRID(AVE)ID(PK)

PD

0󰀟25X

NRILOAD2

a

1bDNILOADD

VIN

50(1bD)

󰀣

J

NeTransformerTurnsRatioe

numberofsecondaryturnsnumberofprimaryturns

heTransformerEfficiency(typically0󰀟95)RILOADelaILOADlalbILOADlFIGURE17󰀟FlybackRegulatorFormulas

ThisformulacanalsobeusedtocalculatethemaximumESRofasingleoutputregulator󰀟

Atthispoint󰀷refertothissamesectionintheStep-UpReg-ulatorDesignProcedureformoreinformationregardingtheselectionofCOUT󰀟

C󰀟CalculatetheminimumvalueofCC58󰀟5cCOUTcVOUTc(VOUTa(VIN(min)cN))CCt

RC2cVIN(min)cN

D󰀟CalculatethemaximumESRoftheaVOUTandbVOUToutputcapacitorsinparallel󰀟

8󰀟7c10b3cVIN(min)cVOUTcN

ESRallESRbs

RILOAD(max)c(VOUTa(VIN(min)cN))

19

ApplicationHints(Continued)

3󰀟OutputVoltageSelection

ThissectionisforapplicationsusingtheLM1577-ADJ󰁋LM2577-ADJ󰀟SkipthissectioniftheLM1577-12󰁋LM2577-12orLM1577-15󰁋LM2577-15isbeingused󰀟

WiththeLM1577-ADJ󰁋LM2577-ADJ󰀷theoutputvoltageisgivenby

VOUTe1󰀟23V(1aR1󰁋R2)ResistorsR1andR2dividetheoutputvoltagedownsoitcanbecomparedwiththeLM1577-ADJ󰁋LM2577-ADJinter-nal1󰀟23Vreference󰀟ForadesiredoutputvoltageVOUT󰀷selectR1andR2sothat

R1V

eOUTb1R21󰀟23V4󰀟DiodeSelection

Theswitchingdiodeinaflybackconvertermustwithstandthereversevoltagespecifiedbythefollowingequation󰀟VIN

VReVOUTa

N

Asuitablediodemusthaveareversevoltageratinggreaterthanthis󰀟InadditionitmustberatedformorethantheaverageandpeakdiodecurrentslistedinFigure17󰀟5󰀟InputCapacitorSelection

Theprimaryofaflybacktransformerdrawsdiscontinuouspulsesofcurrentfromtheinputsupply󰀟Asaresult󰀷afly-Transformer

TypeLPe100mH

Ne1

InputVoltage5V5V5V10V10V10V12V12V12V15V15V15V

DualOutputVoltage

g10Vg12Vg15Vg10Vg12Vg15Vg10Vg12Vg15Vg10Vg12Vg15V

backregulatorgeneratesmorenoiseattheinputsupplythanastep-upregulator󰀷andthisrequiresalargerbypasscapacitortodecoupletheLM1577󰁋LM2577VINpinfromthisnoise󰀟Formostapplications󰀷alowESR󰀷1󰀟0mFcapwillbesufficient󰀷ifitisconnectedveryclosetotheVINandGroundpins󰀟

Inadditiontothisbypasscap󰀷alargercapacitor(t47mF)shouldbeusedwheretheflybacktransformerconnectstotheinputsupply󰀟Thiswillattenuatenoisewhichmayinter-ferewithothercircuitsconnectedtothesameinputsupplyvoltage󰀟

6󰀟SnubberCircuit

A‘‘snubber’’circuitisrequiredwhenoperatingfrominputvoltagesgreaterthan10V󰀷orwhenusingatransformerwithLPt200mH󰀟Thiscircuitclampsavoltagespikefromthetransformerprimarythatoccursimmediatelyaftertheoutputswitchturnsoff󰀟Withoutit󰀷theswitchvoltagemayexceedthe65Vmaximumrating󰀟AsshowninFigure19󰀷thesnub-berconsistsofafastrecoverydiode󰀷andaparallelRC󰀟TheRCvaluesareselectedforswitchclampvoltage(VCLAMP)thatis5Vto10VgreaterthanVSW(OFF)󰀟UsethefollowingequationstocalculateRandC󰀥CtRs

0󰀟02cLPcIP(PK)2(VCLAMP)2b(VSW(OFF))2

MaximumOutputCurrent325mA275mA225mA700mA575mA500mA800mA700mA575mA900mA825mA700mA

19󰀟2c10b4LPcIP(PK)2

Powerdissipation(andpowerrating)oftheresistoris󰀥

VCLAMPaVSW(OFF)bVIN2

Pe󰁋R

2

󰀣

VCLAMPaVSW(OFF)bVIN2

c

2

J󰀣J

J

1

ThefastrecoverydiodemusthaveareversevoltageratinggreaterthanVCLAMP󰀟

󰀣

2

LPe200mHNe0󰀟5

3

LPe250mHNe0󰀟5

Transformer

Type

123

Manufacturers’PartNumbersAIE326-0637330-0202330-0203

PulsePE-65300PE-65301PE-65302

RencoRL-2580RL-2581RL-2582

TL󰁋H󰁋11468–19

FIGURE19󰀟SnubberCircuit

FIGURE18󰀟FlybackTransformerSelectionGuide

20

ApplicationHints(Continued)

FLYBACKREGULATORCIRCUITEXAMPLE

ThecircuitofFigure20producesg15V(at225mAeach)fromasingle5Vinput󰀟TheoutputregulationofthiscircuitisshowninFigures21and22󰀷whiletheloadtransientre-sponseisshowninFigures23and24󰀟SwitchingwaveformsseeninthiscircuitareshowninFigure25󰀟

TL󰁋H󰁋11468–20

T1ePulseEngineering󰀷PE-65300D1󰀷D2e1N5821

FIGURE20󰀟FlybackRegulatorEasilyProvidesDualOutputs

TL󰁋H󰁋11468–21TL󰁋H󰁋11468–22

FIGURE21󰀟LineRegulation(Typical)ofFlyback

RegulatorofFigure20󰀷a15VOutputFIGURE22󰀟LineRegulation(Typical)ofFlyback

RegulatorofFigure20󰀷b15VOutput

21

ApplicationHints(Continued)

TL󰁋H󰁋11468–24

TL󰁋H󰁋11468–23

FIGURE23󰀟LoadTransientResponseofFlyback

RegulatorofFigure20󰀷a15VOutput

A󰀌OutputVoltageChange󰀷100mV󰁋divB󰀌OutputCurrent󰀷100mA󰁋divHorizontal󰀌10ms󰁋div

FIGURE24󰀟LoadTransientResponseofFlyback

RegulatorofFigure20󰀷b15VOutput

A󰀌OutputVoltageChange󰀷100mV󰁋divB󰀌OutputCurrent󰀷100mA󰁋divHorizontal󰀌10ms󰁋div

TL󰁋H󰁋11468–25

FIGURE25󰀟SwitchingWaveformsofFlybackRegulatorofFigure20󰀷EachOutputLoadedwith60X

A󰀌Switchpinvoltage󰀷20V󰁋divB󰀌Primarycurrent󰀷2A󰁋div

C󰀌a15VSecondarycurrent󰀷1A󰁋div

D󰀌a15VOutputripplevoltage󰀷100mV󰁋divHorizontal󰀌5ms󰁋div

22

PhysicalDimensionsinches(millimeters)

TO-3MetalCanPackage(K)

OrderNumberLM1577K-12󰁋883󰀷LM1577K-15󰁋883󰀷orLM1577K-ADJ󰁋883

NSPackageNumberK04A

23

PhysicalDimensionsinches(millimeters)(Continued)

0󰀟300WideSOPackage(M)

OrderNumberLM2577M-12󰀷LM2577M-15orLM2577M-ADJ

NSPackageNumberM24B

MoldedDual-In-LinePackage(N)

OrderNumberLM2577N-12󰀷LM2577N-15󰀷orLM2577N-ADJ

NSPackageNumberN16A

24

PhysicalDimensionsinches(millimeters)(Continued)

TO-220󰀷StraightLeads(T)

OrderNumberLM2577T-12󰀷LM2577T-15󰀷orLM2577T-ADJ

NSPackageNumberTO5A

TO-220󰀷BentStaggeredLeads(T)

OrderNumberLM2577T-12FlowLB03󰀷LM2577T-15FlowLB03󰀷orLM2577T-ADJFlowLB03

NSPackageNumberT05D

25

LM1577󰁋LM2577SeriesSIMPLESWITCHERStep-UpVoltageRegulatorPhysicalDimensionsinches(millimeters)(Continued)

5-LeadTO-263(S)

OrderNumberLM2577S-12󰀷LM2577S-15orLM2577S-ADJ

NSPackageNumberTS5B

LIFESUPPORTPOLICY

NATIONAL’SPRODUCTSARENOTAUTHORIZEDFORUSEASCRITICALCOMPONENTSINLIFESUPPORTDEVICESORSYSTEMSWITHOUTTHEEXPRESSWRITTENAPPROVALOFTHEPRESIDENTOFNATIONALSEMICONDUCTORCORPORATION󰀟Asusedherein󰀌1󰀟Lifesupportdevicesorsystemsaredevicesorsystemswhich󰀷(a)areintendedforsurgicalimplantintothebody󰀷or(b)supportorsustainlife󰀷andwhosefailuretoperform󰀷whenproperlyusedinaccordancewithinstructionsforuseprovidedinthelabeling󰀷canbereasonablyexpectedtoresultinasignificantinjurytotheuser󰀟

NationalSemiconductorCorporation2900SemiconductorDriveNationalSemiconductorGmbHLivry-Gargan-Str󰀟10NationalSemiconductorJapanLtd󰀟SumitomoChemical2󰀟Acriticalcomponentisanycomponentofalifesupportdeviceorsystemwhosefailuretoperformcanbereasonablyexpectedtocausethefailureofthelifesupportdeviceorsystem󰀷ortoaffectitssafetyoreffectiveness󰀟

NationalSemiconductorHongKongLtd󰀟13thFloor󰀷StraightBlock󰀷NationalSemiconductoresDoBrazilLtda󰀟RueDeputadoLacordaFrancoNationalSemiconductor(Australia)Pty󰀷Ltd󰀟Building16