LM3495 Emulated Peak Current Mode Buck …

1 FBSNSFPWMPGNDCSLLGILIMSW/CSHHGBOOSTCFRFB 2 RFB1 CORILIMCINQ1Q2 CBD1 VINVO LM3495 SGNDFREQ/SYNCCOMP/SDVINVLIN5 TRACKCDDCCRCRFRQVLIN5 CSYNCL1 FEBRUARY2006 REVISEDAPRIL2013LM3495 EmulatedPeakCurrentModeBuckControllerfor LowOutputVoltageCheckforSamples:LM34951 FEATURESDESCRIPTIONTheLM3495isaPWMbuckre gulatorwhich2 FeedbackAccuracy: 1%noisewhichtypicallylimitscurrentmodeop erationatextremelyshortdutycyclesandhigh operating Low-SideSensing, ,andcanalsobe HiccupModeCurrentLimitProtectionalsovery faulttolerantwithbothswitchnodeshort,Eli minatesThermalRunawayDuringFaulthiccupmo de, ,outputofanothersupplymaketheLM3495versa tileSynchronizableandefficient. On-ChipGateDriversAPPLICATIONS SoftOutputDischargeDuringShutdown WideInputVoltageBuckConverterswithLow StartupintoOutputPre-BiasVoltage,HighAcc uracyOutputs Operationfroma SingleInputRail CoreLogicRegulators AdaptiveDutyCycleLimit High-EfficiencyBuckRegulation TSSOP-16 PackageTypicalApplication1 Pleasebeawarethatanimportantnoticeconcer ningavailability,standardwarranty,anduse in 2006 2013, FEBRUARY2006 (TopView)SeePackageNumberPW0016A JA= 155 C/WPINDESCRIPTIONSBOOST(Pin1) (Pin2) (Pin3) (Pin4) (Pin5) fixed20 A (Pin6) (Pin7) (Pin8) ,a (Pin9) ,connecta resistordivider(smallerthan10k forbetterprecision) , (Pin10) (Pin11) (Pin12)

2 (Pin13) minimum1 F (Pin14) F (Pin15) (Pin16) 2006 2013, FEBRUARY2006 (1)(2)VIN,ILIM (3) ,HG ,FREQ,FPWM,VLIN5,SNS,LG,CSL 65 C to+150 CLeadTemperature(soldering,10sec)260 CSolderingInformationInfraredorConvectio n(15sec)235 CESDR ating(4)2kV(1) ,seetheElectricalCharacteristics.(2)If Military/Aerospacespecifieddevicesarereq uired,pleasecontacttheTISalesOffice/Dist ributorsforavailabilityandspecifications .(3)Anextendednegativevoltagelimitof 2 Vappliesfora durationof20nsperswitchingcycle(4)Thehum anbodymodelis a 100pFcapacitordischargedthrougha (1)SupplyVoltageRange(VIN) 40 C to+125 C(1) , 2006 2013,TexasInstrumentsIncorporatedSubmitD ocumentationFeedback3 ProductFolderLinks:LM3495LM3495 SNVS410F FEBRUARY2006 25 C only.

3 LimitsinboldfacetypeapplyoverthefullOper atingJunctionTemperature(TJ) ,design, 25 C, ,VIN= (1)MaxUnitsSYSTEMPARAMETERS-20 C to85 C to125 < VIN< 18V,COMP/SD= < COMP/SD< > , < ,Shutdown,VIN= 18V33 AIILIMILIMPinSourceCurrent182022 AVILIM-MAXM aximumCurrentLimitSenseVoltage200mVISDCOMP/SDPinPull-upcurrentCOMP/SD= AVHICCUPCOMP/SDPinHiccupThreshold2 VtDELAYH iccupDelay16 CyclestCOOLCoolDownTimeUntilRestart4096 CyclestSSInternalSoftstartTime400 CyclesVOVPOverVoltageProtectionThresholdAsa %ofnominaloutputvoltage116125132%IFPWMFPWMPinPull-upCurrentFPWM= ,COMP/SD> RDISSNSPinDischargeFETRDSONSNS= ,COMP/SD= 0V350440530 GATEDRIVEIBOOSTBOOSTPinLeakageCurrentBOO ST- SW= SW= resistanceHigh-SideFETD riverPull-downONRDS2 BOOST- SW= resistanceLow-SideFETD riverPull-upONRDS3 VLIN5= resistanceLow-SideFETD riverPull-downONRDS4 VLIN5= resistanceOSCILLATORRADJ= 150k 200fSWPWMF requencyRADJ= 450500550kHzRADJ= ,fSW= 500kHz125nstON-MAXA daptiveMaximumOn-timeLimitVO= ,fSW= 500kHz750nstOFF-MINM inimumOff-time300nsERRORAMPgMTransconduc tance750 mhoBW-3dBOpenLoopBandwidthCOMP/SDFloatin g5 MHzIFBFBPinBiasCurrentVFB= (1)

4 Typicalspecificationsrepresentthemostlik elyparametricnormat25 C 2006 2013, FEBRUARY2006 REVISEDAPRIL2013 ElectricalCharacteristics(continued)Spec ificationswithstandardtypeareforTJ= 25 C only;limitsinboldfacetypeapplyovertheful lOperatingJunctionTemperature(TJ) ,design, 25 C, ,VIN= (1)MaxUnitsISOURCECOMP/SDPinSourceCurren tVFB= ,COMP/SD= AISINKCOMP/SDPinSinkCurrentVFB= ,COMP/SD= AVCOMP-HICOMP/SDPinVoltageHighClampVFB= 12V,VLIN5 Current = (2)VIN= ,VLIN5 Current = JA155 C/WResistanceTSDT hermalShutdownThreshold150 CTSD-HYST hermalShutdownHysteresis15 C(2) 2006 2013,TexasInstrumentsIncorporatedSubmitD ocumentationFeedback5 ProductFolderLinks:LM3495LM3495 SNVS410F FEBRUARY2006 12 Vunlessspecified,TA= 25 C ,IO= 2006 2013, FEBRUARY2006 REVISEDAPRIL2013 TypicalPerformanceCharacteristics(contin ued)VIN= 12 Vunlessspecified,TA= 25 C ,IO= ,IO= ,VO= 12V,VO= 12V,VO= ,IO= 0 AVIN= ,VO= ,IO= 2006 2013,TexasInstrumentsIncorporatedSubmitD ocumentationFeedback7 ProductFolderLinks.

5 LM3495LM3495 SNVS410F FEBRUARY2006 (continued)VIN= 12 Vunlessspecified,TA= 25 C 12V,VO= ,IO= 5 AVIN= ,VO= ,IO= 12V,VO= ,IO= 0 AVIN= ,VO= ,IO= 12V,VO= ,IO= 0 AVIN= 12V,VO= ,IO= 2006 2013, FEBRUARY2006 REVISEDAPRIL2013 TypicalPerformanceCharacteristics(contin ued)VIN= 12 Vunlessspecified,TA= 25 C 12V,VO= ,NoLoadVIN= 5V,VO= , 2006 2013,TexasInstrumentsIncorporatedSubmitD ocumentationFeedback9 ProductFolderLinks:LM3495LM3495 SNVS410F FEBRUARY2006 (continued)VIN= 12 Vunlessspecified,TA= 25 C 12V,VO= ,NoLoadVIN= 5V,VO= , 12V,VO= ,IO= 5 AVIN= 12V,VO= , 2006 2013,TexasInstrumentsIncorporatedProduct FolderLinks: LM3495 FBSNSFPWMPGNDCSLLGILIMSW/CSHHGBOOSTCFRFB 2 RFB1 CORILIMCINQ1Q2 CBD11 F25V2 x 100 k1H10 m10 kVIN = 12V 10%VO = , 10A LM3495 SGNDFREQ/ k10 kVLIN5 CSYNC100 k FEBRUARY2006 REVISEDAPRIL2013 TypicalApplicationCircuitCopyright 2006 2013,TexasInstrumentsIncorporatedSubmitD ocumentationFeedback11 ProductFolderLinks: LM3495 VLIN5 VINTRACKFBCOMP/SDCSLLGILIMSW/CSHHGBOOST+ -EAgm++INTERNAL SOFT-STARTHICCUP+-+-PWMCOMP+-20 PAPWM LOGIC CONTROLANDDRIVER CONTROL2 VRAMPGENERATORAND SLOPE +-VLIN5 SHOOT-THROUGHPROTECTADAPTIVE DUTY CYCLEAND SKIP MODE CONTROLOSCILLATORANDSYNCHRONIZATIONCONTR OLIRAMPIFREQIFREQCLAMPED.

6 LO PAFROM LGTO SHOOT-THROUGHPROTECTSHUTDOWNVREF= PALM3495 SNVS410F FEBRUARY2006 2006 2013,TexasInstrumentsIncorporatedProduct FolderLinks: LM3495 VOUT1 TRACKRT2RT1 RFB2 RFB1 FBVOUT2 VSSVFBLM3495 Master Power FEBRUARY2006 REVISEDAPRIL2013 APPLICATIONSINFORMATIONTHEORYOFOPERATION TheLM3495isanadvanced, on, enabledduringsoftstarttoprotectagainsta theoutputcapacitoroftheLM3495regulatorha sbeenchargeduptosomepre-biaslevelbeforet heconverterisenabled, , ,oncesoft-startis completethezero-crossthresholddecreaseso ver16cyclesandthenis disabled,allowingtheconvertertosinkcurre ntattheoutputif disabled,thisFETis turnedontodischargetheoutputcapacitorina theLM3495is usedina systemwitha pre-biasattheoutputthepowersupplyprovidi ngthepre-biasmustbeabletosupplyenoughcur rentforthe500 masterpowersupplyduringsoftstartbyconnec tinga resistordividertotheTRACKpin(Figure30).

7 Inthisway, , notbeingused, 2006 2013,TexasInstrumentsIncorporatedSubmitD ocumentationFeedback13 ProductFolderLinks: LM3495 ( LM3495 )(Master Supply) = VOUT2RT1RT1 + RT2( LM3495 )(Master Supply) = VOUT1RT1RT1 + RT2LM3495 SNVS410F FEBRUARY2006 (VOUT1) andtheLM3495outputvoltage(VOUT2) ,theequationgoverningthevaluesofthetrack ingdividerresistorsRT1andRT2is:(1)Theabo veequationis , 1% themastersupplyvoltageVOUT1is 5V,forexample, 1%.A timingdiagramforthisexample,theequalsoft starttimecase,is shownin , ,thetrackingresistorscanbedeterminedbase donthefollowingequation:(2)Again,a valueof10k 1%is recommendedforRT2. FortheexamplecaseofVOUT1= 5 VandVOUT2= , 1%.A timingdiagramforthisexample,thecaseofequ alslewrates,is shownin 2006 2013,TexasInstrumentsIncorporatedProduct FolderLinks: LM3495 RFRQ =fSW - x 103k:, fSW in kHz VO = xRFB1 RFB1 + FEBRUARY2006 , ,therebycreatinga ,andis determinedbya pairoffeedbackresistorsusingthefollowing equation:(3)InsteadystateFPWM mode,theinductorcurrentcanflowfromthedra intothesourceofthelow-sideFET,keepingthe converterincontinuousconductionmode(CCM) (D= VO/VIN) overallloadconditions,andit allowstheconvertertosinkcurrentattheoutp utif setbya resistor,RFRQ, desiredswitchingfrequency,fSW, canbedeterminedbyusingthefollowingequati on.

8 (4)SKIPMODEOPERATIONIf theFPWM pinisleftopen-circuited,theLM3495canente rintoSKIP modeoperation, (flowingfromtheswitchnodetotheoutputnode ), ,however, 'diode-emulation'modeallowstheconvertert ooperateindiscontinuousconductionmode(DC M).InDCM, minimumon-timecomparatorpreventsthedutyc ycleduringDCMfromdecreasingbelow80%ofthe steadystatedutycycle, , ,thecontrollogicwilldisablethehigh-sideF ETforonecycle,effectivelyskippinga ,inputvoltage, ,butenergyis , ,thezero-crosscomparatoris "on-the-fly"changesfromFPWM modetoSKIP modearenotrecommendedduetothepossibility ofdiscontinuityin 100pFcouplingcapacitor,CSYNC, asshownin Figure33. InorderfortheLM3495tosynchronizeproperly , , resistor,RFRQ, theexternalclockfailsandthecouplingcapac itorontheclocksideis groundedorpulledtoa 2006 2013,TexasInstrumentsIncorporatedSubmitD ocumentationFeedback15 ProductFolderLinks: LM3495 LGSW/CSHHGBOOSTLM3495D1 CBOOTVLIN5L1Q1Q2 VIN+CoFREQ/SYNCLM3495 External Clock100 pFRFRQCSYNCLM3495 SNVS410F FEBRUARY2006 theexternalclockfailslow, (SwitchingperiodTSW= 1/fSW).

9 Theexternalclockfailshigh, ,theinternaloscillatortakesoverandswitch esata fixed1 , andonceit is , clockpulseis firstdetected, shortburstofclockpulsescanresultin s forthehigh-sideFETif ,theBOOST pinvoltagemustbeatleastonethresholdvolta ge,VGS(th), greaterthanVIN. Thisvoltageis suppliedfroma localchargepumpstructurewhichconsistsofa F capacitor,shownin ,whichis theoutputofa VINdropsbelow4V, thereforeVLIN5-VD, whereVDis , , 2006 2013,TexasInstrumentsIncorporatedProduct FolderLinks: LM3495 RILIM =20 PAICL x FEBRUARY2006 builtin (UVLO) theoutputvoltageexceeds125%ofthesteadyst atetargetvoltageforlongerthan4 s. Thehigh-sideFETis turnedoffandthelow-sideFETis thisconditionuntileithertheVINpinvoltage is cycledtoground,ortheCOMP/SDpinvoltageis ,IO, ,VDS, is comparedagainstthevoltageofa fixed,internal20 A currentsourceanda user-selectedresistor,RILIM.

10 ThevalueofRILIM fora desiredcurrentlimitthreshold,ICL, canbeselectedwiththefollowingequation:(5 )RILIMis currentlimiteventis sensedwhenVDSexceedsVILIM.(VILIM= 20 A x RILIM). Thehigh-sideswitchis disabledforthefollowingcycleandthelow-si deFETis theCOMP/SDpinvoltageexceeds2 Vanda high-sideFETon-pulseis skipped,theLM3495incrementsa 4 16high-gatepulsesareskippedconsecutively whileCOMP/SDstaysabove2V, activ