LM5000 High Voltage Switch Mode Regulator (Rev. D)

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  • Manufacturer or author: Texas Instruments, Incorporated [SNVS176,D]
  • PDF pages: 24

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www.ti.com SNVS176D –MAY 2004–REVISED MARCH 2007 LM5000HighVoltageSwitchModeRegulator Check forSamples: LM5000 1FEATURES DESCRIPTION The LM5000 is a monolithicintegratedcircuit 2• 80V InternalSwitch specificallydesignedand optimizedforflyback,boost• OperatingInputVoltageRange of3.1Vto40V or forwardpower converterapplications.The internal

  • Pin SelectableOperatingFrequency power switchisratedfora maximum of 80V, witha currentlimitset to 2A. Protectingthe power switch– 300kHz/700kHz (-3) are currentlimitand thermalshutdown circuits.The– 600kHz/1.3MHz (-6) currentmode controlscheme provides excellent
  • AdjustableOutput Voltage rejectionoflinetransientsand cycle-by-cyclecurrent limiting.An externalcompensationpinand thebuilt-in• ExternalCompensation slope compensationallowthe user to optimizethe• InputUndervoltageLockout frequencycompensation.Other distinctivefeatures• Softstart includesoftstartto reduce stressesduringstart-up and an externalshutdown pin forremote ON/OFF• CurrentLimit control.There are two operatingfrequencyranges• Over Temperature Protection available.The LM5000-3 ispinselectableforeither• ExternalShutdown 300kHz (FS Grounded) or 700kHz (FS Open). The
  • Small 16-Lead TSSOP or 16-Lead WSON LM5000-6 is pin selectableforeither600kHz (FS Grounded) or 1.3MHz (FS Open). The device isPackage availableina low profile16-leadTSSOP package or a thermallyenhanced 16-leadWSON package.APPLICATIONS
  • FlybackRegulator
  • Forward Regulator
  • Boost Regulator
  • DSL Modems
  • DistributedPower Converters TypicalApplicationCircuit Figure1. LM5000 FlybackConverter Pleasebe aware thatan importantnoticeconcerningavailability,standardwarranty,and use incriticalapplicationsof Texas Instrumentssemiconductorproductsand disclaimerstheretoappearsattheend ofthisdatasheet. 2Alltrademarksarethepropertyoftheirrespectiveowners. PRODUCTION DATA informationiscurrentas ofpublicationdate. Copyright© 2004–2007,Texas InstrumentsIncorporatedProductsconform to specificationsper the terms of the Texas Instrumentsstandardwarranty.Productionprocessingdoes not necessarilyincludetestingofallparameters.

SNVS176D –MAY 2004–REVISED MARCH 2007 www.ti.com Connection Diagram Figure2. Top View PIN DESCRIPTIONS Pin Name Function 1 COMP Compensationnetworkconnection.Connectedtotheoutputofthevoltageerroramplifier.The RC compenstionnetworkshouldbe connectedfromthispintoAGND. An additional100pF highfrequency capacitortoAGND isrecommended. 2 FB Outputvoltagefeedbackinput. 3 SHDN Shutdown controlinput,Open = enable,Ground = disable. 4 AGND Analogground,connectdirectlytoPGND. 5 PGND Power ground. 6 PGND Power ground. 7 PGND Power ground. 8 PGND Power ground. 9 SW Power switchinput.Switchconnectedbetween SW pinsand PGND pins 10 SW Power switchinput.Switchconnectedbetween SW pinsand PGND pins 11 SW Power switchinput.Switchconnectedbetween SW pinsand PGND pins 12 BYP Bypass-DecoupleCapacitorConnection,0.1µF ceramiccapacitorrecommended. 13 VIN Analogpower input.A smallRC filterisrecommended, tosuppresslineglitches.Typicalvaluesof10Ω and ≥ 0.1µF arerecommended. 14 SS SoftstartInput.Externalcapacitorand internalcurrentsourcesetsthesoftstarttime. 15 FS Switchingfrequencyselectinput.Open = Fhigh.Ground = Flow 16 TEST Factorytestpin,connecttoground. - Exposed Pad Connecttosystemgroundplaneforreducedthermalresistance. undersideofWSON package

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www.ti.com SNVS176D –MAY 2004–REVISED MARCH 2007 These deviceshave limitedbuilt-inESD protection.The leadsshouldbe shortedtogetherorthedeviceplacedinconductivefoam duringstorageorhandlingtopreventelectrostaticdamage totheMOS gates. AbsoluteMaximum Ratings(1)(2) VIN -0.3Vto40V SW Voltage -0.3Vto80V FB Voltage -0.3Vto5V COMP Voltage -0.3Vto3V AllOtherPins -0.3Vto7V Maximum JunctionTemperature 150°C Power Dissipation(3) InternallyLimited Lead Temperature 216°C Infrared(15sec.) 235°C ESD Susceptibility(4) Human Body Model 2kV Machine Model 200V StorageTemperature −65°C to+150°C (1) Absolutemaximum ratingsarelimitsbeyond whichdamage tothedevicemay occur.OperatingRatingsareconditionsforwhichthe deviceisintendedtobe functional,butdeviceparameterspecificationsmay notbe ensured.Forensuredspecificationsand test conditions,see theElectricalCharacteristics. (2) IfMilitary/Aerospacespecifieddevicesarerequired,pleasecontacttheTexas InstrumentsSalesOffice/Distributorsforavailabilityand specifications. (3) The maximum allowablepower dissipationisa functionofthemaximum junctiontemperature,TJ(MAX),thejunction-to-ambientthermal resistance,θJA,and theambienttemperature,TA.See theElectricalCharacteristicstableforthethermalresistanceofvariouslayouts. The maximum allowablepower dissipationatany ambienttemperatureiscalculatedusing:PD (MAX) = (TJ(MAX) − TA)/θJA.Exceeding themaximum allowablepower dissipationwillcause excessivedietemperature,and theregulatorwillgo intothermalshutdown. (4) The human body model isa 100 pF capacitordischargedthrougha 1.5kΩ resistorintoeach pin.The machine model isa 200pF capacitordischargeddirectlyintoeach pin. OperatingConditions OperatingJunctionTemperatureRange (1) −40°C to+125°C SupplyVoltage(1) 3.1Vto40V (1) Supplyvoltage,biascurrentproductwillresultinaditionaldevicepower dissipation.Thispower may be significant.The thermal dissipationdesignshouldtakethisintoaccount. ElectricalCharacteristics SpecificationsinstandardtypefaceareforTJ = 25°C and thosewithboldfacetypeapplyoverthefullOperating Temperature Range (TJ = −40°C to+125°C) Unlessotherwisespecified.VIN = 12V and IL = 0A,unlessotherwisespecified. Symbol Parameter Conditions Min (1) Typ (2) Max (1) Units IQ QuiescentCurrent FB = 2V (NotSwitching) 2.0 2.5 mAFS = 0V FB = 2V (NotSwitching) 2.1 2.5 mAFS = Open VSHDN = 0V 18 30 µA VFB Feedback Voltage 1.2330 1.259 1.2840 V ICL SwitchCurrentLimit 1.35 2.0 2.7 A %V FB /ΔVIN Feedback VoltageLine 3.1V≤ VIN ≤ 40V 0.001 0.04 %/V Regulation IB FB PinBiasCurrent(3) 55 200 nA (1) Alllimitsspecifiedatroom temperature(standardtypeface)and attemperatureextremes(boldtypeface).Allroom temperaturelimitsare 100% productiontested.AlllimitsattemperatureextremesarespecifiedviacorrelationusingstandardStatisticalQualityControl(SQC) methods.Alllimitsareused tocalculateAverageOutgoingQualityLevel(AOQL). (2) Typicalnumbers areat25°C and representthemost likelynorm. (3) BiascurrentflowsintoFB pin. Copyright© 2004–2007,Texas InstrumentsIncorporated SubmitDocumentationFeedback 3 ProductFolderLinks:LM5000

SNVS176D –MAY 2004–REVISED MARCH 2007 www.ti.com ElectricalCharacteristics(continued) SpecificationsinstandardtypefaceareforTJ = 25°C and thosewithboldfacetypeapplyoverthefullOperating Temperature Range (TJ = −40°C to+125°C) Unlessotherwisespecified.VIN = 12V and IL = 0A,unlessotherwisespecified. Symbol Parameter Conditions Min (1) Typ (2) Max (1) Units BV OutputSwitchBreakdown TJ = 25°C, ISW = 0.1µA 80 V Voltage TJ = -40°C to+ 125°C, ISW = 76 0.5µA VIN InputVoltageRange 3.1 40 V gm ErrorAmp Transconductance ΔI= 5µA 150 410 750 µmho AV ErrorAmp VoltageGain 280 V/V D MAX Maximum DutyCycle FS = 0V 85 90 % LM5000-3 Maximum DutyCycle FS = 0V 85 90 % LM5000-6 TMIN Minimum On Time 165 ns fS SwitchingFrequencyLM5000- FS = 0V 240 300 360

3 FS = Open 550 700 840 kHz

SwitchingFrequencyLM5000- FS = 0V 485 600 715 6 FS = Open 1.055 1.3 1.545 MHz ISHDN Shutdown PinCurrent VSHDN = 0V −1 -2 µA IL SwitchLeakage Current VSW = 80V 0.008 5 µA R DSON SwitchR DSON ISW = 1A 160 445 m Ω ThSHDN SHDN Threshold OutputHigh 0.9 0.6 V OutputLow 0.6 0.3 V UVLO On Threshold 2.74 2.92 3.10 V OffThreshold 2.60 2.77 2.96 V OVP VCOMP Trip 0.67 V ISS SoftstartCurrent 8 11 14 µA θJA ThermalResistance TSSOP, Package only 150 °C/W

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VIN (V) 100 150 200 250 300 350 400 R DS (ON) (m:) 25oC 125oC -40oC TEMPERATURE ( oC) FEEDBACK VOLTAGE (V) 1.2300 1.2400 1.2500 1.2600 1.2700 1.2800 -40 -20 0 20 40 60 80 100 120 0 5 10 15 20 25 30 35 40 VIN (V) Iq (mA) -40oC 125oC 25oC 0 5 10 15 20 25 30 35 40 VIN (V) Iq (mA) -40oC 125oC 25oC -40oC 25oC 125oC Iq (mA) 1.000 1.200 1.400 1.600 1.800 2.000 2.200 2.400 2.600 2.800 3.000 VIN (V) 0 5 10 15 20 25 30 35 40 VIN (V) Iq (mA) 1.000 1.200 1.400 1.600 1.800 2.000 2.200 2.400 2.600 2.800 3.000 0 5 10 15 20 25 30 35 40 -40oC 25oC 125oC LM5000 www.ti.com SNVS176D –MAY 2004–REVISED MARCH 2007 TypicalPerformance Characteristics Iq(non-switching)vs VIN @ fSW = 300kHz Iq(non-switching)vs VIN @ fSW = 700kHz Figure3. Figure4. Iq(switching)vs VIN @ fSW = 300kHz Iq(switching)vs VIN @ fSW = 700kHz Figure5. Figure6. Vfb vs Temperature R DS(ON) vs VIN @ ISW =1A Figure7. Figure8. Copyright© 2004–2007,Texas InstrumentsIncorporated SubmitDocumentationFeedback 5 ProductFolderLinks:LM5000

-40 -20 0 20 40 60 80 100 120 TEMPERATURE ( oC) 270 280 290 300 310 320 330 fSW (kHz) fsw (kHz) TEMPERATURE ( oC) -40 -20 0 20 40 60 80 100 120 630 650 670 690 710 730 750 770 VIN (V) 0 5 10 15 20 25 30 35 40 fsw (kHz) 285 290 295 300 305 310 315 FREQUENCY (KHZ) 630 650 670 690 710 730 750 770 VIN (V) 0 5 10 15 20 25 30 35 40 VIN (V) 0 5 10 15 20 25 30 35 40 CURRENT LIMIT (A) 1.5 1.55 1.6 1.65 1.7 1.75 1.8 1.85 1.9 1.95 TEMPERATURE ( oC) CURRENT LIMIT (A) -40 -20 0 20 40 60 80 100 120 1.5 1.55 1.6 1.65 1.7 1.75 1.8 1.85 1.9 1.95 LM5000 SNVS176D –MAY 2004–REVISED MARCH 2007 www.ti.com TypicalPerformance Characteristics(continued) CurrentLimitvs Temperature CurrentLimitvs VIN Figure9. Figure10. fSW vs.VIN @ FS = Low (-3) fSW vs.VIN @ FS = OPEN (-3) Figure11. Figure12. fSW vs.Temperature @ FS = Low (-3) fSW vs.Temperature @ FS = OPEN (-3) Figure13. Figure14.

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VIN (V) 0 5 10 15 20 25 30 35 40 BYP PIN VOLTAGE (V) 8 125oC 25oC -40oC Gm [Pmho] TEMPERATURE ( oC) -40 -20 0 20 40 60 80 100 120 250 300 350 400 450 500 550 600 -40 -20 0 20 40 60 80 100 120 TEMPERATURE ( oC) 520 540 560 580 600 620 640 fSW (kHz) -40 -20 0 20 40 60 80 100 120 TEMPERATURE ( oC) 1.14 1.18 1.22 1.26 1.30 1.34 1.38 fSW (kHz) LM5000 www.ti.com SNVS176D –MAY 2004–REVISED MARCH 2007 TypicalPerformance Characteristics(continued) fSW vs.Temperature @ FS = Low (-6) fSW vs.Temperature @ FS = OPEN (-6) Figure15. Figure16. ErrorAmp. Transconductance vs Temp. BYP Pin Voltagevs VIN Figure17. Figure18. Copyright© 2004–2007,Texas InstrumentsIncorporated SubmitDocumentationFeedback 7 ProductFolderLinks:LM5000

SNVS176D –MAY 2004–REVISED MARCH 2007 www.ti.com TypicalApplicationDiagrams Figure19. 300 kHz operation,48V output Figure20. 700 kHz operation,48V output

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www.ti.com SNVS176D –MAY 2004–REVISED MARCH 2007 Block Diagram Copyright© 2004–2007,Texas InstrumentsIncorporated SubmitDocumentationFeedback 9 ProductFolderLinks:LM5000

SNVS176D –MAY 2004–REVISED MARCH 2007 www.ti.com BOOST REGULATOR OPERATION The LM5000 utilizesa PWM controlscheme toregulatetheoutputvoltageoverallloadconditions.The operation can bestbe understoodreferringtotheblockdiagramand Figure21.At thestartofeach cycle,theoscillator setsthedriverlogicand turnson theNMOS power deviceconductingcurrentthroughtheinductor,cycle1 of Figure21 (a).Duringthiscycle,the voltageat the COMP pincontrolsthe peak inductorcurrent.The COMP voltagewillincreasewithlargerloadsand decreasewithsmaller.Thisvoltageiscompared withthesummation of the SW volatgeand the ramp compensation.Theramp compensationis used in PWM architecturesto eliminatethesub-harmonicoscillationsthatoccurduringdutycyclesgreaterthan50%. Once thesummation of the ramp compensationand switchvoltageequalsthe COMP voltage,the PWM comparatorresetsthe driver logicturningofftheNMOS power device.The inductorcurrentthenflowsthroughtheoutputdiodetotheload and outputcapacitor,cycle2 ofFigure21 (b).The NMOS power deviceisthensetby theoscillatorattheend of theperiodand currentflowsthroughtheinductoronce again. The LM5000 has dedicatedprotectioncircuitryrunningduringthe normal operationto protectthe IC. The Thermal Shutdown circuitryturnsoffthe NMOS power devicewhen the die temperaturereaches excessive levels.The UVP comparatorprotectsthe NMOS power deviceduringsupplypower startupand shutdown to preventoperationatvoltageslessthantheminimum inputvoltage.The OVP comparatorisused topreventthe outputvoltagefrom risingat no loadsallowingfullPWM operationover allloadconditions.The LM5000 also featuresa shutdown mode. An externalcapacitorsetsthesoftstarttimeby limitingtheerroramp outputrange, as thecapacitorchargesup viaan internal10µA currentsource. The LM5000 isavailableintwo operatingfrequencyranges.The LM5000-3 ispinselectableforeither300kHz (FS Grounded) or 700kHz (FS Open). The LM5000-6 ispin selectableforeither600kHz (FS Grounded) or 1.3MHz (FS Open) Operation Figure21. SimplifiedBoost ConverterDiagram (a)FirstCycle ofOperation(b)Second Cycle Of Operation CONTINUOUS CONDUCTION MODE The LM5000 isa current-mode,PWM regulator.When used as a boostregulatortheinputvoltageissteppedup to a higheroutputvoltage.In continuousconductionmode (when the inductorcurrentnever reacheszero at steadystate),theboostregulatoroperatesintwo cycles. Inthefirstcycleofoperation,shown inFigure21 (a),thetransistorisclosedand thediodeisreversebiased. Energyiscollectedintheinductorand theloadcurrentissuppliedby C OUT .

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:R FB1 = RFB2 x VOUT - 1.259 1.259 VOUT = VIN 1-D , D' = (1-D) = VIN VOUT LM5000 www.ti.com SNVS176D –MAY 2004–REVISED MARCH 2007 The second cycleisshown inFigure21 (b).Duringthiscycle,thetransistorisopen and thediodeisforward biased.The energystoredintheinductoristransferredtotheloadand outputcapacitor. The ratioofthesetwo cyclesdeterminestheoutputvoltage.The outputvoltageisdefinedapproximatelyas: where

  • D isthedutycycleoftheswitch
  • D and D ′ willbe requiredfordesigncalculations (1) SETTING THE OUTPUT VOLTAGE The outputvoltageissetusingthe feedbackpinand a resistordividerconnectedto the outputas shown in Figure19.The feedbackpinisalwaysat1.259V,so theratioofthefeedbackresistorssetstheoutputvoltage. (2) INTRODUCTION TO COMPENSATION Figure22. (a)Inductorcurrent.(b)Diode current. The LM5000 isa currentmode PWM regulator.The signalflowofthiscontrolscheme has two feedbackloops, one thatsensesswitchcurrentand one thatsensesoutputvoltage. Copyright© 2004–2007,Texas InstrumentsIncorporated SubmitDocumentationFeedback 11 ProductFolderLinks:LM5000

'iL = (in Amps) VIND 2Lfs VINR DSON 0.144 fs L > ( ) D ( ) D D' +1 (in H) Hz1 2S(RC + RO )CC fPC = Hz1fZC = 2SR C C C LM5000 SNVS176D –MAY 2004–REVISED MARCH 2007 www.ti.com To keep a currentprogrammed controlconverterstableabove duty cyclesof 50%, the inductormust meet certaincriteria.The inductor,alongwithinputand outputvoltage,willdeterminetheslopeofthecurrentthrough theinductor(seeFigure22 (a)).Iftheslopeoftheinductorcurrentistoogreat,thecircuitwillbe unstableabove dutycyclesof50%. The LM5000 providesa compensationpin(COMP) tocustomizethevoltageloopfeedback.Itisrecommended thata seriescombinationof R C and C C be used forthe compensationnetwork,as shown inFigure19. The seriescombinationofR C and C C introducespole-zeropairaccordingtothefollowingequations: (3) where

  • R O istheoutputimpedance oftheerroramplifier,850kΩ (4) For most applications,performancecan be optimizedby choosingvalueswithintherange5kΩ ≤ R C ≤ 20kΩ and 680pF ≤ C C ≤ 4.7nF. COMPENSATION Thissectionwillpresenta generaldesignproceduretohelpinsurea stableand operationalcircuit.The designs inthisdatasheetare optimizedforparticularrequirements.Ifdifferentconversionsare required,some of the components may need to be changed to ensure stability.Below isa setof generalguidelinesindesigninga stablecircuitforcontinuousconductionoperation(loadsgreaterthan100mA), inmost allcases thiswillprovide forstabilityduringdiscontinuousoperationas well.The power components and theireffectswillbe determined first,thenthecompensationcomponents willbe chosen toproducestability. INDUCTOR SELECTION To ensurestabilityatdutycyclesabove 50%, theinductormust have some minimum valuedeterminedby the minimum inputvoltageand themaximum outputvoltage.Thisequationis: where
  • fsistheswitchingfrequency
  • D isthedutycycle
  • R DSON istheON resistanceoftheinternalswitch (5) Thisequationisonlygood fordutycyclesgreaterthan50% (D>0.5). (6) The inductorripplecurrentisimportantfora few reasons.One reasonisbecause thepeak switchcurrentwillbe theaverageinductorcurrent(inputcurrent)plusΔiL.Care must be takentomake surethattheswitchwillnot reach itscurrentlimitduringnormal operation.The inductormust alsobe sizedaccordingly.Itshouldhave a saturationcurrentratinghigherthanthepeak inductorcurrentexpected.The outputvoltagerippleisalsoaffected by thetotalripplecurrent. DC GAIN AND OPEN-LOOP GAIN Sincethecontrolstageoftheconverterformsa completefeedbackloopwiththepower components,itformsa closed-loopsystem thatmust be stabilizedtoavoidpositivefeedbackand instability.A valueforopen-loopDC gain willbe required,from which you can calculate,or place,polesand zeros to determinethe crossover frequencyand the phase margin.A highphase margin (greaterthan 45°) isdesiredforthe beststabilityand transientresponse.For thepurposeofstabilizingtheLM5000, choosinga crossoverpointwellbelow where the righthalfplanezeroislocatedwillensuresufficientphase margin.A discussionoftherighthalfplanezeroand checkingthecrossoverusingtheDC gainwillfollow.

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fZC = 1 2SC C R C (in Hz) fPC = 1 2S(RC + RO )CC (in Hz) (in Hz)RHPzero = VOUT (D')2 2S,LOAD L fZ1 = 1 2SR ESR C OUT (in Hz) fP1 = 1 2S(RESR + RL)COUT (in Hz) LM5000 www.ti.com SNVS176D –MAY 2004–REVISED MARCH 2007 OUTPUT CAPACITOR SELECTION The choiceofoutputcapacitorsissomewhat more arbitrary.Itisrecommended thatlow ESR (EquivalentSeries Resistance,denoted R ESR ) capacitorsbe used such as ceramic,polymer electrolytic,or low ESR tantalum. HigherESR capacitorsmay be used butwillrequiremore compensationwhich willbe explainedlateron inthe section.The ESR isalsoimportantbecause itdeterminestheoutputvoltagerippleaccordingtotheapproximate equation: ΔVOUT ≊ 2ΔiLR ESR (inVolts) (7) Afterchoosingtheoutputcapacitoryou can determinea pole-zeropairintroducedintothecontrolloopby the followingequations: (8) where

  • R L istheminimum loadresistancecorrespondingtothemaximum loadcurrent (9) The zerocreatedby theESR oftheoutputcapacitorisgenerallyveryhighfrequencyiftheESR issmall.Iflow ESR capacitorsare used itcan be neglected.IfhigherESR capacitorsare used see the HIGH OUTPUT CAPACITOR ESR COMPENSATION section. RIGHT HALF PLANE ZERO A currentmode controlboostregulatorhas an inherentrighthalfplanezero(RHP zero).Thiszerohas theeffect ofa zerointhegainplot,causingan imposed +20dB/decade on therolloff,buthas theeffectofa poleinthe phase, subtractinganother90° in the phase plot.This can cause undesirableeffectsifthe controlloop is influencedby thiszero.To ensuretheRHP zerodoes notcause instabilityissues,thecontrolloopshouldbe designedtohave a bandwidthof½ thefrequencyoftheRHP zeroorless.Thiszerooccursata frequencyof: where
  • ILOAD isthemaximum loadcurrent (10) SELECTING THE COMPENSATION COMPONENTS The firststepinselectingthecompensationcomponents R C and C C istoseta dominantlow frequencypolein the controlloop.Simply choose valuesforR C and C C withinthe ranges givenin the INTRODUCTION TO COMPENSATION sectiontosetthispoleinthearea of10Hz to100Hz. The frequencyofthepolecreatedis determinedby theequation: where
  • R O istheoutputimpedance oftheerroramplifier,850kΩ (11) Since R C isgenerallymuch lessthan R O , itdoes not have much effecton the above equationand can be neglecteduntila valueischosen tosetthezerofZC .fZC iscreatedtocanceloutthepolecreatedby theoutput capacitor,fP1.The outputcapacitorpolewillshiftwithdifferentloadcurrentsas shown by theequation,so setting thezeroisnotexact.Determinetherange offP1 overtheexpectedloadsand thensetthezerofZC toa point approximatelyinthemiddle.The frequencyofthiszeroisdeterminedby: (12) Copyright© 2004–2007,Texas InstrumentsIncorporated SubmitDocumentationFeedback 13 ProductFolderLinks:LM5000

m1 # VINR DSON L (in V/s) n = 1+ 2mc m1 (no unit) Leff = L (D')2 Zc (in rad/s)2fs nD'# ADC(DB) = 20log10 {[(ZcLeff)// RL]//RL} (in dB) R FB1 + RFB2 R FB2 ( ) gm R O D' R DSON fPC2 = 1 2SC C2 (RC //RO ) (in Hz) LM5000 SNVS176D –MAY 2004–REVISED MARCH 2007 www.ti.com Now R C can be chosen withtheselectedvalueforC C .Check tomake surethatthepolefPC isstillinthe10Hz to 100Hz range,change each valueslightlyifneeded toensurebothcomponent valuesare intherecommended range.Aftercheckingthedesignattheend ofthissection,thesevaluescan be changed a littlemore tooptimize performanceifdesired.Thisisbestdone inthelabon a bench,checkingtheloadstepresponsewithdifferent valuesuntiltheringingand overshooton theoutputvoltageattheedge oftheloadstepsisminimal.Thisshould produce a stable,highperformancecircuit.For improvedtransientresponse,highervaluesof R C (withinthe range ofvalues)shouldbe chosen.Thiswillimprovetheoverallbandwidthwhich makes theregulatorrespond more quicklytotransients.Ifmore detailisrequired,orthemost optimalperformanceisdesired,refertoa more indepthdiscussionofcompensatingcurrentmode DC/DC switchingregulators. HIGH OUTPUT CAPACITOR ESR COMPENSATION When usingan outputcapacitorwitha highESR value,orjusttoimprovetheoverallphase marginofthecontrol loop,anotherpolemay be introducedtocancelthezerocreatedby theESR. Thisisaccomplishedby adding anothercapacitor,C C2 ,directlyfromthecompensationpinVC toground,inparallelwiththeseriescombinationof R C and C C .The poleshouldbe placedatthesame frequencyas fZ1,theESR zero.The equationforthispole follows: (13) To ensurethisequationisvalid,and thatC C2 can be used withoutnegativelyimpactingtheeffectsofR C and C C , fPC2 must be greaterthan10fPC . CHECKING THE DESIGN The finalstepistocheck thedesign.Thisistoensurea bandwidthof½ or lessofthefrequencyoftheRHP zero.Thisisdone by calculatingtheopen-loopDC gain,ADC .Afterthisvalueisknown, you can calculatethe crossovervisuallyby placinga −20dB/decadeslopeateach pole,and a +20dB/decadeslopeforeach zero.The pointatwhichthegainplotcrossesunitygain,or0dB, isthecrossoverfrequency.Ifthecrossoverfrequencyis atlessthan½ theRHP zero,thephase marginshouldbe highenough forstability.The phase margincan also be improvedsome by addingC C2 as discussedearlierinthesection.The equationforADC isgivenbelow with additionalequationsrequiredforthecalculation: (14) (15) (16) (17) mc ≊ 0.072fs(inA/s) (18) where

  • R L istheminimum loadresistance
  • VIN isthemaximum inputvoltage
  • R DSON isthevaluechosen fromthegraph"RDSON vs.VIN "intheTypicalPerformanceCharacteristics section (19) SWITCH VOLTAGE LIMITS In a flybackregulator,the maximum steady-statevoltageappearingat the switch,when itisoff,issetby the transformerturnsratio,N, theoutputvoltage,VOUT ,and themaximum inputvoltage,VIN (Max): VSW(OFF) = VIN (Max)+ (VOUT +VF)/N where
  • VF istheforwardbiasedvoltageoftheoutputdiode,and istypically0.5VforSchottkydiodesand 0.8Vfor ultra-fastrecoverydiodes (20)

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www.ti.com SNVS176D –MAY 2004–REVISED MARCH 2007 Incertaincircuits,thereexistsa voltagespike,VLL,superimposedon topofthesteady-statevoltage.Usually, thisvoltagespikeiscaused by thetransformerleakageinductanceand/ortheoutputrectifierrecoverytime.To “clamp” the voltageat the switchfrom exceedingitsmaximum value,a transientsuppressorinserieswitha diodeisinsertedacrossthetransformerprimary. Ifpoorcircuitlayouttechniquesareused,negativevoltagetransientsmay appearon theSwitchpin.Applyinga negativevoltage(withrespectto the IC'sground)to any monolithicIC pin causes erraticand unpredictable operationofthatIC.ThisholdstruefortheLM5000 IC as well.When used ina flybackregulator,thevoltageat theSwitchpincan go negativewhen theswitchturnson.The “ringing”voltageattheswitchpiniscaused by the output diode capacitanceand the transformerleakage inductanceforming a resonant circuitat the secondary(ies).The resonantcircuitgeneratesthe “ringing” voltage,which gets reflectedback throughthe transformerto the switchpin.There are two common methods to avoidthisproblem.One isto add an RC snubberaround theoutputrectifier(s).The valuesoftheresistorand thecapacitormust be chosen so thatthe voltageattheSwitchpindoes notdrop below −0.4V.The resistormay range invaluebetween 10Ω and 1 kΩ, and thecapacitorwillvaryfrom0.001μF to0.1μF. Adding a snubberwill(slightly)reducetheefficiencyofthe overallcircuit. The othermethod toreduceor eliminatethe“ringing” istoinserta Schottkydiodeclamp between theSW pin and thePGND pin.The reversevoltageratingofthediodemust be greaterthantheswitchoffvoltage. OUTPUT VOLTAGE LIMITATIONS The maximum outputvoltageof a boost regulatoristhe maximum switchvoltageminus a diode drop.In a flybackregulator,themaximum outputvoltageisdeterminedby theturnsratio,N, and thedutycycle,D, by the equation: VOUT ≈ N × VIN × D/(1− D) (21) The dutycycleofa flybackregulatorisdeterminedby thefollowingequation: (22) Theoretically,themaximum outputvoltagecan be as largeas desired— justkeep increasingtheturnsratioofthe transformer.However, thereexistssome physicallimitationsthatpreventthe turnsratio,and thusthe output voltage,from increasingto infinity.The physicallimitationsare capacitancesand inductancesinthe LM5000 switch,theoutputdiode(s),and thetransformer— such as reverserecoverytimeoftheoutputdiode(mentioned above). INPUT LINE CONDITIONING A small,low-passRC filtershouldbe used attheinputpinoftheLM5000 iftheinputvoltagehas an unusually largeamount oftransientnoise.Additionally,theRC filtercan reducethedissipationwithinthedevicewhen the inputvoltageishigh. FlybackRegulatorOperation The LM5000 isideallysuitedforuse intheflybackregulatortopology.The flybackregulatorcan producea single outputvoltage,ormultipleoutputvoltages. The operationof a flybackregulatorisas follows:When the switchison, currentflowsthroughthe primary windingofthetransformer,T1,storingenergyinthemagneticfieldofthetransformer.Note thattheprimaryand secondarywindingsareoutofphase,so no currentflowsthroughthesecondarywhen currentflowsthroughthe primary.When theswitchturnsoff,themagneticfieldcollapses,reversingthevoltagepolarityoftheprimaryand secondarywindings.Now rectifierD5 isforwardbiasedand currentflowsthroughit,releasingtheenergystored inthetransformer.Thisproducesvoltageattheoutput. The outputvoltageiscontrolledby modulatingthepeak switchcurrent.Thisisdone by feedingback a portionof theoutputvoltagetotheerroramp, which amplifiesthedifferencebetween thefeedbackvoltageand a 1.259V reference.The erroramp outputvoltageiscompared toa ramp voltageproportionaltotheswitchcurrent(i.e., inductorcurrentduringtheswitchon time).The comparatorterminatestheswitchon timewhen thetwo voltages areequal,therebycontrollingthepeak switchcurrenttomaintaina constantoutputvoltage. Copyright© 2004–2007,Texas InstrumentsIncorporated SubmitDocumentationFeedback 15 ProductFolderLinks:LM5000

SNVS176D –MAY 2004–REVISED MARCH 2007 www.ti.com Figure23. LM5000 FlybackConverter

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www.ti.com SNVS176D –MAY 2004–REVISED MARCH 2007 ITEM PART NUMBER DESCRIPTION VALUE C 1 C4532X7R2A105MT Capacitor,CER, TDK 1µ,100V C 2 C4532X7R2A105MT Capacitor,CER, TDK 1µ,100V C 3 C1206C224K5RAC Capacitor,CER, KEMET 0.22µ,50V C 4 C1206C104K5RAC Capacitor,CER, KEMET 0.1µ,50V C 5 C1206C104K5RAC Capacitor,CER, KEMET 0.1µ,50V C 6 C1206C101K1GAC Capacitor,CER, KEMET 100p,100V C 7 C1206C104K5RAC Capacitor,CER, KEMET 0.1µ,50V C 8 C4532X7S0G686M Capacitor,CER, TDK 68µ,4V C 9 C4532X7S0G686M Capacitor,CER, TDK 68µ,4V C 10 C1206C221K1GAC Capacitor,CER, KEMET 220p,100V C 11 C1206C102K5RAC Capacitor,CER, KEMET 1000p,500V D 1 BZX84C10-NSA Central,10V Zener,SOT-23 D 2 CMZ5930B-NSA Central,16V Zener,SMA D 3 CMPD914-NSA Central,Switching,SOT-23 D 4 CMPD914-NSA Central,Switching,SOT-23 D 5 CMSH3-40L-NSA Central,Schottky,SMC T 1 A0009-A Coilcraft,Transformer R 1 CRCW12064992F Resistor 49.9K R 2 CRCW12061001F Resistor 1K R 3 CRCW12061002F Resistor 10K R 4 CRCW12066191F Resistor 6.19K R 5 CRCW120610R0F Resistor 10 R 6 CRCW12062003F Resistor 200K R 7 CRCW12061002F Resistor 10K Q 1 CXT5551-NSA Central,NPN, 180V U 1 LM5000-3 Regulator,TI Copyright© 2004–2007,Texas InstrumentsIncorporated SubmitDocumentationFeedback 17 ProductFolderLinks:LM5000

www.ti.com 1-Nov-2013 Addendum-Page 1 PACKAGING INFORMATION Orderable Device Status (1) Package Type Package Drawing Pins Package Qty Eco Plan (2) Lead/Ball Finish (6) MSL Peak Temp (3) Op Temp (°C) Device Marking (4/5) Samples LM5000-3MTC NRND TSSOP PW 16 92 TBD Call TI Call TI -40 to 125 LM5000 3MTC LM5000-3MTC/NOPB ACTIVE TSSOP PW 16 92 Green (RoHS & no Sb/Br) CU SN Level-1-260C-UNLIM -40 to 125 LM5000 3MTC LM5000-3MTCX NRND TSSOP PW 16 2500 TBD Call TI Call TI -40 to 125 LM5000 3MTC LM5000-3MTCX/NOPB ACTIVE TSSOP PW 16 2500 Green (RoHS & no Sb/Br) CU SN Level-1-260C-UNLIM -40 to 125 LM5000 3MTC LM5000SD-3/NOPB ACTIVE WSON NHQ 16 1000 Green (RoHS & no Sb/Br) CU SN Level-1-260C-UNLIM -40 to 125 5000-3 LM5000SD-6/NOPB ACTIVE WSON NHQ 16 1000 Green (RoHS & no Sb/Br) CU SN Level-1-260C-UNLIM -40 to 125 5000-6 LM5000SDX-3/NOPB ACTIVE WSON NHQ 16 4500 Green (RoHS & no Sb/Br) CU SN Level-1-260C-UNLIM -40 to 125 5000-3 LM5000SDX-6/NOPB ACTIVE WSON NHQ 16 4500 Green (RoHS & no Sb/Br) CU SN Level-1-260C-UNLIM -40 to 125 5000-6 (1) The marketing status values are defined as follows: ACTIVE: Product device recommended for new designs. LIFEBUY: TI has announced that the device will be discontinued, and a lifetime-buy period is in effect. NRND: Not recommended for new designs. Device is in production to support existing customers, but TI does not recommend using this part in a new design. PREVIEW: Device has been announced but is not in production. Samples may or may not be available. OBSOLETE: TI has discontinued the production of the device. (2) Eco Plan - The planned eco-friendly classification: Pb-Free (RoHS), Pb-Free (RoHS Exempt), or Green (RoHS & no Sb/Br) - please check http://www.ti.com/productcontent for the latest availability information and additional product content details. TBD: The Pb-Free/Green conversion plan has not been defined. Pb-Free (RoHS): TI's terms "Lead-Free" or "Pb-Free" mean semiconductor products that are compatible with the current RoHS requirements for all 6 substances, including the requirement that lead not exceed 0.1% by weight in homogeneous materials. Where designed to be soldered at high temperatures, TI Pb-Free products are suitable for use in specified lead-free processes. Pb-Free (RoHS Exempt): This component has a RoHS exemption for either 1) lead-based flip-chip solder bumps used between the die and package, or 2) lead-based die adhesive used between the die and leadframe. The component is otherwise considered Pb-Free (RoHS compatible) as defined above. Green (RoHS & no Sb/Br): TI defines "Green" to mean Pb-Free (RoHS compatible), and free of Bromine (Br) and Antimony (Sb) based flame retardants (Br or Sb do not exceed 0.1% by weight in homogeneous material) (3) MSL, Peak Temp. - The Moisture Sensitivity Level rating according to the JEDEC industry standard classifications, and peak solder temperature.

www.ti.com 1-Nov-2013 Addendum-Page 2 (4) There may be additional marking, which relates to the logo, the lot trace code information, or the environmental category on the device. (5) Multiple Device Markings will be inside parentheses. Only one Device Marking contained in parentheses and separated by a "~" will appear on a device. If a line is indented then it is a continuation of the previous line and the two combined represent the entire Device Marking for that device. (6) Lead/Ball Finish - Orderable Devices may have multiple material finish options. Finish options are separated by a vertical ruled line. Lead/Ball Finish values may wrap to two lines if the finish value exceeds the maximum column width. Important Information and Disclaimer:The information provided on this page represents TI's knowledge and belief as of the date that it is provided. TI bases its knowledge and belief on information provided by third parties, and makes no representation or warranty as to the accuracy of such information. Efforts are underway to better integrate information from third parties. TI has taken and continues to take reasonable steps to provide representative and accurate information but may not have conducted destructive testing or chemical analysis on incoming materials and chemicals. TI and TI suppliers consider certain information to be proprietary, and thus CAS numbers and other limited information may not be available for release. In no event shall TI's liability arising out of such information exceed the total purchase price of the TI part(s) at issue in this document sold by TI to Customer on an annual basis.

*All dimensions are nominal Device Package Type Package Drawing Pins SPQ Reel Diameter (mm) Reel Width W1 (mm) (mm) (mm) (mm) (mm) W (mm) Pin1 Quadrant PACKAGE MATERIALS INFORMATION www.ti.com 6-Nov-2015 Pack Materials-Page 1

*All dimensions are nominal Device Package Type Package Drawing Pins SPQ Length (mm) Width (mm) Height (mm) LM5000-3MTCX TSSOP PW 16 2500 367.0 367.0 35.0 LM5000-3MTCX/NOPB TSSOP PW 16 2500 367.0 367.0 35.0 LM5000SD-3/NOPB WSON NHQ 16 1000 210.0 185.0 35.0 LM5000SD-6/NOPB WSON NHQ 16 1000 210.0 185.0 35.0 LM5000SDX-3/NOPB WSON NHQ 16 4500 367.0 367.0 35.0 LM5000SDX-6/NOPB WSON NHQ 16 4500 367.0 367.0 35.0 PACKAGE MATERIALS INFORMATION www.ti.com 6-Nov-2015 Pack Materials-Page 2

www.ti.com SDA16A (Rev A)

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