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TPS51218

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TPS51218www.ti.comSLUS935–MAY2009

HIGHPERFORMANCE,SINGLESYNCHRONOUSSTEP-DOWN

CONTROLLERFORNOTEBOOKPOWERSUPPLY

FEATURES

WideInputVoltageRange:3Vto28VOutputVoltageRange:0.7Vto2.6VWideOutputLoadRange:0to20A+Built-in0.5%0.7VReference

D-CAP™Modewith100-nsLoadStepResponse

AdaptiveOnTimeControlArchitectureWith4SelectableFrequencySetting

4700ppm/°CRDS(on)CurrentSensingInternal1-msVoltageServoSoftstartPre-ChargedStart-upCapabilityBuiltinOutputDischargePowerGoodOutput

IntegratedBoostSwitchBuilt-inOVP/UVP/OCP

ThermalShutdown(Non-latch)SON-10(DSC)Package

APPLICATIONS

•••

NotebookComputersI/OSupplies

SystemPowerSupplies

•••••

DESCRIPTION

TheTPS51218isasmall-sizedsinglebuckcontrollerwithadaptiveon-timeD-CAP™mode.Thedeviceissuitableforlowoutputvoltage,highcurrent,PCsystempowerrailandsimilarpoint-of-load(POL)powersupplyindigitalconsumerproducts.Asmallpackagewithminimalpin-countsavesspaceonthePCB,whileadedicatedENpinandpre-setfrequencyselectionsminimizedesigneffortrequiredfornewdesigns.Theskip-modeatlightloadcondition,stronggatedriversandlow-sideFETRDS(on)currentsensingsupportslow-lossandhighefficiency,overabroadloadrange.Theconversioninputvoltagewhichisthehigh-sideFETdrainvoltagerangesfrom3Vto28Vandtheoutputvoltagerangesfrom0.7Vto2.6V.Thedevicerequiresanexternal5-Vsupply.TheTPS51218isavailableina10-pinSONpackagespecifiedfrom–40°Cto85°C.

••••••••••

TYPICALAPPLICATIONCIRCUIT

V5INTPS5121812EN345PGOODTRIPENVFBRFGNDVBST10DRVHSWV5INDRVL9876VOUT_GNDUDG-090VINVOUTPleasebeawarethatanimportantnoticeconcerningavailability,standardwarranty,anduseincriticalapplicationsofTexasInstrumentssemiconductorproductsanddisclaimerstheretoappearsattheendofthisdatasheet.

D-CAPisatrademarkofTexasInstruments.

PRODUCTIONDATAinformationiscurrentasofpublicationdate.ProductsconformtospecificationsperthetermsoftheTexasInstrumentsstandardwarranty.Productionprocessingdoesnotnecessarilyincludetestingofallparameters.

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Thesedeviceshavelimitedbuilt-inESDprotection.TheleadsshouldbeshortedtogetherorthedeviceplacedinconductivefoamduringstorageorhandlingtopreventelectrostaticdamagetotheMOSgates.

ORDERINGINFORMATION

–40°Cto85°C

PACKAGEPlasticSONPowerPAD

ORDERINGDEVICE

NUMBERTPS51218DSCRTPS51218DSCT

PINS1010

OUTPUTSUPPLYTapeandreelMinireel

MINIMUMQUANTITY3000250

ECOPLANGreen(RoHSandno

Pb/Br)

ABSOLUTEMAXIMUMRATINGS(1)

overoperatingfree-airtemperaturerange(unlessotherwisenoted)

VALUE

VBST

Inputvoltagerange(2)

VBSTSW

V5IN,EN,TRIP,VFB,RFDRVH

Outputvoltagerange

(2)

(3)

UNIT

–0.3to37–0.3to7–2.0to30–0.3to7–2.0to37–0.3to7–0.5to7–0.3to7150–55to150

°C°CVV

DRVH(3)DRVLPGOOD

JunctiontemperaturerangeStoragetemperaturerange

TJTSTG(1)(2)(3)

Stressesbeyondthoselistedunderabsolutemaximumratingsmaycausepermanentdamagetothedevice.Thesearestressratingsonlyandfunctionaloperationofthedeviceattheseoranyotherconditionsbeyondthoseindicatedunderrecommendedoperatingconditionsisnotimplied.Exposuretoabsolute-maximum-ratedconditionsforextendedperiodsmayaffectdevicereliability.Allvoltagevaluesarewithrespecttothenetworkgroundterminalunlessotherwisenoted.VoltagevaluesarewithrespecttotheSWterminal.

DISSIPATIONRATINGS

2-oz.traceandcopperpadwithsolder.

PACKAGE10pinDSC(1)

(1)

TA<25°CPOWERRATING

1.W

DERATINGFACTORABOVETA=25°C

15mW/°C

TA=85°CPOWERRATING

0.62W

EnhancedthermalconductancebythermalviasisusedbeneaththermalpadasshowninLandPatterninformation.

RECOMMENDEDOPERATINGCONDITIONS

overoperatingfree-airtemperaturerange(unlessotherwisenoted)

MIN

Supplyvoltage

V5INVBST

Inputvoltagerange

SWVBST(1)

EN,TRIP,VFB,RFDRVH

Outputvoltagerange

DRVH(1)DRVLPGOOD

TA(1)2

Operatingfree-airtemperature

VoltagevaluesarewithrespecttotheSWterminal.

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4.5–0.1–1.0–0.1–0.1–1.0–0.1–0.3–0.1–40

TYP

MAX6.534.5286.56.534.56.56.56.585

°CVVUNITV

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ELECTRICALCHARACTERISTICS

overrecommendedfree-airtemperaturerange,V5IN=5V.(Unlessotherwisenoted)

PARAMETER

SUPPLYCURRENTIV5INIV5INSDN

V5INsupplycurrentV5INshutdowncurrent

V5INcurrent,TA=25°C,NoLoad,VEN=5V,VVFB=0.735V

V5INcurrent,TA=25°C,NoLoad,VEN=0VVFBvoltage,CCMcondition(1)

VVFB

VFBregulationvoltage

TA=25°C,skipmodeTA=0°Cto85°C,skipmodeTA=–40°Cto85°C,skipmode

IVFB

VFBinputcurrent

OutputdischargecurrentfromSWpin

VVFB=0.735V,TA=25°C,skipmode

OUTPUTDISCHARGEIDischg

VEN=0V,VSW=0.5V

0.70050.69840.6970

0.70000.70400.70400.70400.01

0.70750.70960.7110

0.2

µAV

320

5001

µAµAV

TESTCONDITIONS

MIN

TYP

MAX

UNIT

INTERNALREFERENCEVOLTAGE

OUTPUTDRIVERSRDRVHRDRVLtD

DRVHresistanceDRVLresistanceDeadtime

Source,IDRVH=–50mASink,IDRVH=50mASource,IDRVL=–50mASink,IDRVL=50mADRVH-offtoDRVL-onDRVL-offtoDRVH-on

VV5IN-VBST,IF=10mA,TA=25°CVVBST=34.5V,VSW=28V,TA=25°CTA=25°C

VIN=28V,VOUT=0.7V,RRF=39kΩ,TA=25°C(1)

FromVEN=hightoVOUT=95%PGinfromlower

VTHPGIPGMAXtPGDEL

PGthresholdPGsinkcurrentPGdelay

PGinfromhigherPGhysteresisVPGOOD=0.5VDelayforPGinEnableDisableVEN=5V

RRF=470kΩ,TA=25°C(2)

fSW

Switchingfrequency

RRF=200kΩ,TA=25°C(2)RRF=100kΩ,TA=25°C(2)RRF=39kΩ,TA=25°C(2)

VRF(1)(2)

CCMsettingvoltage

CCMAuto-skip

2663123493951.8

0.5

290340380430

92.5%107.5%2.5%

30.81.8

0.51.0314368411465

VkHz

150710

1.50.71.00.517220.10.0126079

31.82.21.230350.21.00

nsnsΩ

BOOTSTRAPSWITCHVFBSTIVBSTLKtOFF(min)tON(min)SOFTSTARTtss

InternalSStime

195%110%5%61

1.297.5%112.5%7.5%

mAmsms

POWERGOOD

ForwardvoltageVBSTleakagecurrentMinimumoff-timeMinimumon-time

VµA

DUTYANDFREQUENCYCONTROL

LOGICTHRESHOLDANDSETTINGCONDITIONSVENIEN

ENvoltagethresholdENinputcurrent

VµA

Ensuredbydesign.Notproductiontested.

Notproductiontested.TestconditionisVIN=8V,VOUT=1.1V,IOUT=10AusingapplicationcircuitshowninFigure21.SubmitDocumentationFeedback

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ELECTRICALCHARACTERISTICS(continued)

overrecommendedfree-airtemperaturerange,V5IN=5V.(Unlessotherwisenoted)

PARAMETER

PROTECTION:CURRENTSENSEITRIPTCITRIPVTRIP

TRIPsourcecurrentTRIPcurrenttemperaturecoeffficient

Currentlimitthresholdsettingrange

Currentlimitthreshold

VTRIP=1V,TA=25°COnthebasisof25°CVTRIP-GNDVoltageVTRIP=3.0V

VOCL

VTRIP=1.6VVTRIP=0.2VVTRIP=3.0V

VOCLN

NegativecurrentlimitthresholdAutozerocrossadjustablerange

OVPtripthreshold

OVPpropagationdelaytimeOutputUVPtripthresholdOutputUVPpropagationdelaytime

OutputUVPenabledelaytime

FromEnabletoUVPworkableWakeupShutdown

ShutdowntemperatureHysteresis(3)

(3)

TESTCONDITIONSMIN9

TYP104700

MAX11

UNITµAppm/°C

0.235518517–395–215–333

37520025–375–200–2515–15

115%65%0.81.04.203.7

120%

170%11.24.383.9314510

339521533–355–185–17–3125%

VTRIP=1.6VVTRIP=0.2VPositiveNegativeOVPdetect50-mVoverdriveUVPdetect

VAZCADJ

PROTECTION:UVPANDOVPVOVPtOVPDELVUVPtUVPDELtUVPENUVLOVUVV5IN

V5INUVLOthreshold

4.504.1

Vµs

75%1.21.4

msms

THERMALSHUTDOWNTSDN(3)

Thermalshutdownthreshold

°C

Ensuredbydesign.Notproductiontested.

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DEVICEINFORMATION

DSCPACKAGE(TOPVIEW)

PGOODTRIPENVFBRF

12345TPS51218DSC109876VBSTDRVHSWV5INDRVL

GNDThermalpadisusedasanactiveterminalofGND.

PINFUNCTIONS

PINNAMEDRVHDRVLENGNDPGOODNO.963ThermalPad1I/OOOIIODESCRIPTIONHigh-sideMOSFETdriveroutput.TheSWnodereferencedfloatingdriver.ThegatedrivevoltageisdefinedbythevoltageacrossVBSTtoSWnodebootstrapflyingcapacitorSynchronousMOSFETdriveroutput.TheGNDreferenceddriver.ThegatedrivevoltageisdefinedbyV5INvoltage.SMPSenablepin.ShorttoGNDtodisablethedevice.GroundPowerGoodwindowcomparatoropendrainoutput.Pullupwithresistorto5Vorappropriatesignalvoltage.Continuouscurrentcapacityis1mA.PGOODgoeshigh1msafterVFBbecomeswithinspecifiedlimits.Powerbad,ortheterminalgoeslow,aftera2-µsdelay.Switchingfrequencyselection.ConnectaresistancetoselectswitchingfrequencyasshowninTable1.RF5ITheswitchingfrequencyisdetectedandstoredintointernalregistersduringstartup.ThispinalsocontrolsAuto-skiporforcedCCMselection.PulldowntoGNDwithresistor:Auto-SkipConnecttoPGOODwithresistor:forcedCCMafterPGOODbecomeshigh.SW8ISwitchnode.Ahigh-sideMOSFETgatedrivereturn.Alsousedforontimegenerationandoutputdischarge.OCLdetectionthresholdsettingpin.10µAatroomtemperature,4700ppm/°CcurrentissourcedandsettheOCLtripvoltageasfollows.TRIP2IVOCL=V5INVBSTVFB7104IIIVTRIP8(0.2V≤VTRIP≤3V)5V+30%/–10%powersupplyinput.Supplyinputforhigh-sideMOSFETdriver(bootstrapterminal).ConnectaflyingcapacitorfromthispintotheSWpin.InternallyconnectedtoV5INviabootstrapMOSFETswitch.SMPSfeedbackinput.Connectthefeedbackresistordivider.Copyright©2009,TexasInstrumentsIncorporatedSubmitDocumentationFeedback

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FUNCTIONALBLOCKDIAGRAM

0.7V–30%+UV0.7V+10/15%+Delay+0.7V–5/10%VBSTPGOOD

+0.7V+20%Enable/SSControlOVControlLogicENVFB

+PWMDHRVSW

XCON+++0.7VRampComp10mATRIP

x(-1/8)+OCPtONOne-ShotFCCMx(1/8)Auto-skip+ZCV5INDHRLGND

Auto-skip/FCCMFrequencySettingDetectorRF

TPS51218UDG-09065

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TYPICALCHARACTERISTICS

V5INSUPPLYCURRENT

JUNCTIONTEMPERATURE

V5INSHUTDOWNCURRENT

JUNCTIONTEMPERATURE

100020

IV5IN–V5INSupplyCurrent–mA800

IV5INSDN–V5INShutdownCurrent–mAVV5IN=5VVEN=5VVVFB=0.735VNoLoad1816141210820–50VV5IN=5VVEN=0VNoLoad600

400

200

0–50

050100150050100150TJ–JunctionTemperature–°C

Figure1.

OVP/UVPTHRESHOLD

JUNCTIONTEMPERATURE

TJ–JunctionTemperature–°C

Figure2.

CURRENTSENSECURRENT(ITRIP)

JUNCTIONTEMPERATURE

15020

VOVP/VUVP–OVP/UVPTripThreshold–%VV5IN=5V18

ITRIP–CurrentSenseCurrent–mAOVP1614121082

VV5IN=5VVTRIP=1V100

UVP50

0–50

050100150

0–50

050100150

TJ–JunctionTemperature–°C

Figure3.

TJ–JunctionTemperature–°C

Figure4.

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TYPICALCHARACTERISTICS(continued)

SWITCHINGFREQUENCY

INPUTVOLTAGE

SWITCHINGFREQUENCY

OUTPUTCURRENT

500

IO=10AAuto-SkipRRF=39kW400

RRF=100kW350

RRF=200kWRRF=470kW1000

fSW–SwitchingFrequency–kHzfSW–SwitchingFrequency–kHz450

FCCM100

Auto-Skip1

VIN=12VRRF=470kW300

250

200

VIN–InputVoltage–V

Figure5.

SWITCHINGFREQUENCY

OUTPUTCURRENT

0.10.001

0.010.1110100

IOUT–OutputCurrent–A

Figure6.

SWITCHINGFREQUENCY

OUTPUTCURRENT

10001000

fSW–SwitchingFrequency–kHz100

fSW–SwitchingFrequency–kHzFCCMFCCM100

Auto-Skip1

VIN=12VRRF=200kW0.10.001

0.01

0.1

100

Auto-Skip1

VIN=12VRRF=100kW0.10.001

0.01

0.1

100

IOUT–OutputCurrent–A

Figure7.

IOUT–OutputCurrent–A

Figure8.

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TYPICALCHARACTERISTICS(continued)

SWITCHINGFREQUENCY

OUTPUTCURRENT

OUTPUTVOLTAGE

OUTPUTCURRENT

10001.12

MODEAuto-SkipFCCMfSW–SwitchingFrequency–kHzFCCM10

Auto-Skip1

VIN=12VRRF=39kW0.10.001

0.01

0.1

100

VOUT–OutputVoltage–V1001.11

1.10

1.09

VIN=12VRRF=470kW1.080.001

0.01

0.1

100

IOUT–OutputCurrent–A

Figure9.OUTPUTVOLTAGE

INPUTVOLTAGE

IOUT–OutputCurrent–A

Figure10.1.1-VEFFICIENCY

OUTPUTCURRENT

100

1.12

Auto-SkipRRF=470kW90

RRF=470kWVOUT=1.1VIOUT=20Ah–Efficiency–%8070605040302010

FCCMVIN(V)812201

100

Auto-SkipVOUT–OutputVoltage–V1.11

1.10

IOUT=0A1.09

1.08

1012

1416

182022

2426

VIN–InputVoltage–V

Figure11.

00.001

0.010.1

IOUT–OutputCurrent–A

Figure12.

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TYPICALCHARACTERISTICS(continued)

Figure13.1.1-VStart-UpWaveform

XXXFigure14.Pre-BiasedStart-UpWaveform

XXXFigure15.1.1-VSoft-StopWaveform

XXXFigure16.1.1-VLoadTransientResponse

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APPLICATIONINFORMATION

GENERALDESCRIPTION

TheTPS51218isahigh-efficiency,singlechannel,synchronousbuckregulatorcontrollersuitableforlowoutputvoltagepoint-of-loadapplicationsinnotebookcomputersandsimilardigitalconsumerapplications.ThedevicefeaturesproprietaryD-CAP™modecontrolcombinedwithadaptiveon-timearchitecture.Thiscombinationisidealforbuildingmodernlowdutyratio,ultra-fastloadstepresponseDC-DCconverters.Theoutputvoltagerangesfrom0.7Vto2.6V.Theconversioninputvoltagerangeisfrom3Vto28V.TheD-CAP™modeusestheESRoftheoutputcapacitor(s)tosensecurrentinformation.Anadvantageofthiscontrolschemeisthatitdoesnotrequireanexternalphasecompensationnetwork,helpingthedesignerwithease-of-useandrealizinglowexternalcomponentcountconfiguration.TheswitchingfrequencyisselectablefromfourpresetvaluesusingaresistorconnectedfromtheRFpintoground.Adaptiveon-timecontroltracksthepresetswitchingfrequencyoverawiderangeofinputandoutputvoltages,whileitincreasestheswitchingfrequencyatstep-upofload.TheRFpinalsoservesinselectingbetweenauto-skipmodeandforcedcontinuousconductionmodeforlightloadconditions.ThestronggatedriversoftheTPS51218allowlowRDS(on)FETsforhighcurrentapplications.

ENABLEANDSOFTSTART

WhentheENpinvoltagerisesabovetheenablethreshold,(typically1.2V)thecontrollerentersitsstart-upsequence.Thefirst250µscalibratestheswitchingfrequencysettingresistanceattachedatRFtoGNDandstorestheswitchingfrequencycodeininternalregisters.Avoltageof0.1VisappliedtoRFformeasurement.Switchingisinhibitedduringthisphase.Inthesecondphase,internalDACstartsrampingupthereferencevoltagefrom0Vto0.7V.Thisrampingtimeis750µs.Smoothandconstantrampupoftheoutputvoltageismaintainedduringstartupregardlessofloadcurrent.

ADAPTIVEON-TIMED-CAP™CONTROL

TPS51218doesnothaveadedicatedoscillatorthatdeterminesswitchingfrequency.However,thedevicerunswithpseudo-constantfrequencybyfeed-forwardingtheinputandoutputvoltagesintoitson-timeone-shottimer.Theadaptiveon-timecontroladjuststheon-timetobeinverselyproportionaltotheinputvoltageandproportionaltotheoutputvoltage(tON∝VOUT/VIN).Thismakestheswitchingfrequencyfairlyconstantinsteadystateconditionsoverwideinputvoltagerange.TheswitchingfrequencyisselectablefromfourpresetvaluesbyaresistorconnectedtoRFasshowninTable1.(Leavingtheresistanceopensetstheswitchingfrequencytothelowestvalue,290kHz.However,itisrecommendedtoapplyoneoftheresistancesonthetableinanyapplicationdesigns.)

Table1.ResistorandSwitchingFrequency

RESISTANCE(RRF)

(kΩ)

47020010039

SWITCHINGFREQUENCY(fSW)

(kHz)

290340380430

Theoff-timeismodulatedbyaPWMcomparator.TheVFBnodevoltage(themidpointofresistordivider)iscomparedtotheinternal0.7-Vreferencevoltageaddedwitharampsignal.Whenbothsignalsmatch,thePWMcomparatorassertsthesetsignaltoterminatetheoff-time(turnoffthelow-sideMOSFETandturnonhigh-sideMOSFET).ThesetsignalbecomesvalidiftheinductorcurrentlevelisbelowOCPthreshold,otherwisetheoff-timeisextendeduntilthecurrentleveltobecomebelowthethreshold.

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SMALLSIGNALMODEL

Fromsmall-signalloopanalysis,abuckconverterusingD-CAP™modecanbesimplifiedasshowninFigure17.SwitchingModulatorVINR1VFBR2PWMControlLogicandDriverDRVHLVOUT++0.7VDRVLIINDICESRIOUT

VoltageDividerRL

VCCOOutputCapacitorUDG-09063

Figure17.SimplifiedModulatorModel

Theoutputvoltageiscomparedwithinternalreferencevoltage(rampsignalisignoredhereforsimplicity).ThePWMcomparatordeterminesthetimingtoturnonthehigh-sideMOSFET.Thegainandspeedofthecomparatorcanbeassumedhighenoughtokeepthevoltageatthebeginningofeachoncyclesubstantiallyconstant.

H(s)=

s´ESR´CO

(1)

Forloopstability,the0-dBfrequency,ƒ0,definedinEquation2needtobelowerthan1/4oftheswitchingfrequency.

f0=

£SW

2p´ESR´CO4

(2)

AccordingtoEquation2,theloopstabilityofD-CAP™modemodulatorismainlydeterminedbythecapacitor's

chemistry.Forexample,specialtypolymercapacitors(SP-CAP)haveCOontheorderofseveral100µFandESRinrangeof10mΩ.Thesemakesf0ontheorderof100kHzorlessandtheloopisstable.However,ceramiccapacitorshaveanƒ0ofmorethan700kHz,whichisnotsuitableforthismodulator.

RAMPSIGNAL

TheTPS51218addsarampsignaltothe0.7-Vreferenceinordertoimproveitsjitterperformance.Asdescribedintheprevioussection,thefeedbackvoltageiscomparedwiththereferenceinformationtokeeptheoutputvoltageinregulation.Byaddingasmallrampsignaltothereference,theS/Nratioattheonsetofanewswitchingcycleisimproved.Thereforetheoperationbecomeslessjitteryandmorestable.Therampsignaliscontrolledtostartwith–7mVatthebeginningofON-cycleandbecomes0mVattheendofOFF-cycleincontinuousconductionsteadystate.

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LIGHTLOADCONDITIONINAUTO-SKIPOPERATION

WithRFpinpulleddowntolowviaRRF,theTPS51218automaticallyreducesswitchingfrequencyatlightloadconditionstomaintainhighefficiency.Astheoutputcurrentdecreasesfromheavyloadcondition,theinductorcurrentisalsoreducedandeventuallycomestothepointthatitsrippledvalleytoucheszerolevel,whichistheboundarybetweencontinuousconductionanddiscontinuousconductionmodes.TherectifyingMOSFETisturnedoffwhenthiszeroinductorcurrentisdetected.Astheloadcurrentfurtherdecreases,theconverterrunsintodiscontinuousconductionmode.Theon-timeiskeptalmostthesameasitwasinthecontinuousconductionmodesothatittakeslongertimetodischargetheoutputcapacitorwithsmallerloadcurrenttothelevelofthereferencevoltage.ThetransitionpointtothelightloadoperationIO(LL)(i.e.,thethresholdbetweencontinuousanddiscontinuousconductionmode)canbecalculatedinEquation3.IO(LL)=where

•

(V-VOUT)´VOUT1

´IN

2´L´fSWVIN

fSWisthePWMswitchingfrequency

(3)

SwitchingfrequencyversusoutputcurrentinthelightloadconditionisafunctionofL,VINandVOUT,butit

decreasesalmostproportionaltotheoutputcurrentfromtheIO(LL)giveninEquation3.Forexample,itis58kHzatIO(LL)/5ifthefrequencysettingis290kHz.

ADAPTIVEZEROCROSSING

TheTPS51218hasanadaptivezerocrossingcircuitwhichperformsoptimizationofthezeroinductorcurrentdetectionatskipmodeoperation.Thisfunctionpursuesideallow-sideMOSFETturningofftimingandcompensatesinherentoffsetvoltageoftheZCcomparatoranddelaytimeoftheZCdetectioncircuit.ItpreventsSW-nodeswing-upcausedbytoolatedetectionandminimizesdiodeconductionperiodcausedbytooearlydetection.Asaresult,betterlightloadefficiencyisdelivered.

FORCEDCONTINUOUSCONDUCTIONMODE

WhentheRFpinistiedhigh,thecontrollerkeepscontinuousconductionmode(CCM)inlightloadcondition.Inthismode,switchingfrequencyiskeptalmostconstantovertheentireloadrangewhichissuitableforapplicationsneedtightcontroloftheswitchingfrequencyatacostoflowerefficiency.TosettheswitchingfrequencytobethesameasAuto-skipmode,itisrecommendedtoconnectRRFtoPGOOD.Inthisway,RFistiedlowpriortosoft-startoperationtosetfrequencyandtiedhighafterpowergoodindicateshigh.

OUTPUTDISCHARGECONTROL

WhenENislow,theTPS51218dischargestheoutputcapacitorusinginternalMOSFETconnectedbetweenSWandGNDwhilehigh-sideandlow-sideMOSFETsarekeptoff.ThecurrentcapabilityofthisMOSFETislimitedtodischargeslowly.

LOW-SIDEDRIVER

Thelow-sidedriverisdesignedtodrivehighcurrentlowRDS(on)N-channelMOSFET(s).Thedrivecapabilityisrepresentedbyitsinternalresistance,whichare1.0ΩforV5INtoDRVLand0.5ΩforDRVLtoGND.Adeadtimetopreventshootthroughisinternallygeneratedbetweenhigh-sideMOSFETofftolow-sideMOSFETon,andlow-sideMOSFETofftohigh-sideMOSFETon.5-VbiasvoltageisdeliveredfromV5INsupply.TheinstantaneousdrivecurrentissuppliedbyaninputcapacitorconnectedbetweenV5INandGND.TheaveragedrivecurrentisequaltothegatechargeatVgs=5Vtimesswitchingfrequency.Thisgatedrivecurrentaswellasthehigh-sidegatedrivecurrenttimes5VmakesthedrivingpowerwhichneedtobedissipatedfromTPS51218package.

HIGH-SIDEDRIVER

Thehigh-sidedriverisdesignedtodrivehighcurrent,lowRDS(on)N-channelMOSFET(s).Whenconfiguredasafloatingdriver,5VofbiasvoltageisdeliveredfromV5INsupply.TheaveragedrivecurrentisalsoequaltothegatechargeatVGS=5Vtimesswitchingfrequency.TheinstantaneousdrivecurrentissuppliedbytheflyingcapacitorbetweenVBSTandSWpins.Thedrivecapabilityisrepresentedbyitsinternalresistance,whichare1.5ΩforVBSTtoDRVHand0.7ΩforDRVHtoSW.

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POWER-GOOD

TheTPS51218haspowergoodoutputthatindicateshighwhenswitcheroutputiswithinthetarget.Thepowergoodfunctionisactivatedaftersoft-starthasfinished.Iftheoutputvoltagebecomeswithin+10%/–5%ofthetargetvalue,internalcomparatorsdetectpower-goodstateandthepower-goodsignalbecomeshighaftera1-msinternaldelay.Iftheoutputvoltagegoesoutsideof+15%/–10%ofthetargetvalue,thepowergoodsignalbecomeslowaftera2-µsinternaldelay.Thepowergoodoutputisanopen-drainoutputandmustbepulledupexternally.

CURRENTSENSEANDOVERCURRENTPROTECTION

TPS51218hascycle-by-cycleovercurrentlimitingcontrol.TheinductorcurrentismonitoredduringtheOFFstateandthecontrollerkeepstheOFFstateduringtheinductorcurrentislargerthantheovercurrenttriplevel.Toprovidebothgoodaccuracyandcosteffectivesolution,theTPS51218supportstemperaturecompensatedMOSFETRDS(on)sensing.TheTRIPpinshouldbeconnectedtoGNDthroughthetripvoltagesettingresistor,RTRIP.TheTRIPterminalsourcesITRIPcurrent,whichis10µAtypicallyatroomtemperature,andthetriplevelissettotheOCLtripvoltageVTRIPasshowninEquation4.NotethatVTRIPislimiteduptoapproximately3Vinternally.

VTRIP(mV)=RTRIP(kW)´ITRIP(mA)

(4)

TheinductorcurrentismonitoredbythevoltagebetweenGNDpadandSWpinsothattheSWpinshouldbeconnectedtothedrainterminalofthelow-sideMOSFETproperly.ITRIPhas4700ppm/°CtemperatureslopetocompensatethetemperaturedependencyoftheRDS(on).GNDisusedasthepositivecurrentsensingnodesothatGNDshouldbeconnectedtothepropercurrentsensingdevice,i.e.thesourceterminalofthelow-sideMOSFET.

AsthecomparisonisdoneduringtheOFFstate,VTRIPsetsvalleyleveloftheinductorcurrent.Thus,theloadcurrentatovercurrentthreshold,IOCP,canbecalculatedinEquation5

æV

TRIP

IOCP=ç

ç8´RDS(on)è

öIIND(ripple)(V-VOUT)´VOUTVTRIP1÷+=+´IN÷28´RDS(on)2´L´fSWVINø

(5)

Inanovercurrentcondition,thecurrenttotheloadexceedsthecurrenttotheoutputcapacitorthustheoutputvoltagetendstofalldown.Eventually,itcrossestheundervoltageprotectionthresholdandshutsdownthecontroller.

Whenthedeviceisoperatingintheforcedcontinuousconductionmode,thenegativecurrentlimit(NCL)protectstheexternalFETfromcarryingtoomuchcurrent.TheNCLdetectthresholdissetasthesameabsolutevalueaspositiveOCLbutnegativepolarity.Pleasebenotedthethresholdstillrepresentsthevalleyvalueoftheinductorcurrent.

OVER/UNDERVOLTAGEPROTECTION

TPS51218monitorsaresistordividedfeedbackvoltagetodetectoverandundervoltage.Whenthefeedbackvoltagebecomeshigherthan120%ofthetargetvoltage,theOVPcomparatoroutputgoeshighandthecircuitlatchesasthehigh-sideMOSFETdriverOFFandthelow-sideMOSFETdriverON.

Whenthefeedbackvoltagebecomeslowerthan70%ofthetargetvoltage,theUVPcomparatoroutputgoeshighandaninternalUVPdelaycounterbeginscounting.Aftera1-msdelay,TPS51218latchesOFFbothhigh-sideandlow-sideMOSFETsdrivers.Thisfunctionisenabledafter1.2msfollowingENhasbecomehigh.

UVLOPROTECTION

TPS51218hasV5INundervoltagelockoutprotection(UVLO).WhentheV5INvoltageislowerthanUVLOthresholdvoltage,theswitchmodepowersupplyshutsoff.Thisisnon-latchprotection.

THERMALSHUTDOWN

TPS51218monitorsthedietemperature.Ifthetemperatureexceedsthethresholdvalue(typically145C),theTPS51218isshutoff.Thisisnon-latchprotection.

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EXTERNALCOMPONENTSSELECTION

SelectingexternalcomponentsissimpleinD-CAP™mode.1.Choosetheinductor.

Theinductancevalueshouldbedeterminedtogivetheripplecurrentofapproximately1/4to1/2ofmaximumoutputcurrent.LargerripplecurrentincreasesoutputripplevoltageandimprovesS/Nratioandhelpsstableoperation.

IIND(ripple)´fSW

V(´

IN(max)-VOUT

)´V

OUT

VIN(max)

IOUT(max)´fSW

V(´

IN(max)-VOUT

)´V

OUT

VIN(max)

(6)

TheinductoralsoneedstohavelowDCRtoachievegoodefficiency,aswellasenoughroomabovepeak

inductorcurrentbeforesaturation.ThepeakinductorcurrentcanbeestimatedinEquation7.IIND(peak)

VIN(max)-VOUT´VOUT

VTRIP1=+´8´RDS(on)L´fSWVIN(max)

()(7)

2.Choosetheoutputcapacitor(s).

Organicsemiconductorcapacitor(s)orspecialtypolymercapacitor(s)arerecommended.Forloopstability,

capacitanceandESRshouldsatisfyEquation2.Forjitterperformance,Equation8isagoodstartingpointtodetermineESR.

ESR=

VOUT´10éëmVùû´(1-D)0.7éëVùû´IIND(ripple)

10éëmVùû´L´fSW

0.7éëVùû

L´fSW

éWù70ëû

(8)

where

•••

Disthedutyratio

theoutputrippledownsloperateis10mV/tSWintermsofVFBterminalvoltageasshowninFigure18tSWistheswitchingperiod

VVFB–FeedbackVoltage–mVtSWx(1-D)10

VRIPPLE(FB)0

t–Time

tSW

Figure18.RippleVoltageDownSlope

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TPS51218SLUS935–MAY2009www.ti.com

3.DeterminethevalueofR1andR2.

Theoutputvoltageisprogrammedbythevoltage-dividerresistor,R1andR2,showninFigure17.R1isconnectedbetweentheVFBpinandtheoutput,andR2isconnectedbetweentheVFBpinandGND.TypicaldesignsbeginwiththeselectionofanR2valuebetween10kΩand20kΩ.DetermineR1usingEquation9.IIND(ripple)´ESRöæ

-Vç÷çOUT÷-0.72øR1=è´R2

0.7

(9)

LAYOUTCONSIDERATIONS

VINTRIP2RF5TPS51218V5IN610mF#2#1VOUT

VFB45DRVLThermalPadGND#3UDG-09066Figure19.GroundSystemofDC/DCConverterUsingtheTPS51218

CertainpointsmustbeconsideredbeforestartingalayoutworkusingtheTPS51218.

•Inductor,VINcapacitor(s),VOUTcapacitor(s)andMOSFETsarethepowercomponentsandshouldbeplacedononesideofthePCB(solderside).Othersmallsignalcomponentsshouldbeplacedonanotherside(componentside).Atleastoneinnerplaneshouldbeinserted,connectedtoground,inordertoshieldandisolatethesmallsignaltracesfromnoisypowerlines.

•AllsensitiveanalogtracesandcomponentssuchasVFB,PGOOD,TRIPandRFshouldbeplacedawayfromhigh-voltageswitchingnodessuchasSW,DRVL,DRVHorVBSTto　avoidcoupling.Useinternallayer(s)asgroundplane(s)andshieldfeedbacktracefrompowertracesand　components.

•TheDC/DCconverterhasseveralhigh-currentloops.Theareaoftheseloopsshouldbeminimizedinordertosuppressgeneratingswitchingnoise.

–ThemostimportantlooptominimizetheareaofisthepathfromtheVINcapacitor(s)throughthehighandlow-sideMOSFETs,andbacktothecapacitor(s)throughground.ConnectthenegativenodeoftheVINcapacitor(s)andthesourceofthelow-sideMOSFETatgroundascloseaspossible.(Refertoloop#1ofFigure19)–Thesecondimportantloopisthepathfromthelow-sideMOSFETthroughinductorandVOUTcapacitor(s),andbacktosourceofthelow-sideMOSFETthroughground.Connectsourceofthelow-sideMOSFETandnegativenodeofVOUTcapacitor(s)atgroundascloseaspossible.(Refertoloop#2ofFigure19)–Thethirdimportantloopisofgatedrivingsystemforthelow-sideMOSFET.Toturnonthelow-sideMOSFET,highcurrentflowsfromV5INcapacitorthroughgatedriverandthelow-sideMOSFET,andback

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•

••••

tonegativenodeofthecapacitorthroughground.Toturnoffthelow-sideMOSFET,highcurrentflowsfromgateofthelow-sideMOSFETthroughthegatedriverandGNDpadofthedevice,andbacktosourceofthelow-sideMOSFETthroughground.ConnectnegativenodeofV5INcapacitor,sourceofthelow-sideMOSFETandGNDpadofthedeviceatgroundascloseaspossible.(Refertoloop#3ofFigure19)SincetheTPS51218controlsoutputvoltagereferringtovoltageacrossVOUTcapacitor,thetop-sideresistorofthevoltagedividershouldbeconnectedtothepositivenodeofVOUTcapacitor.InasamemannerbothbottomsideresistorandGNDpadofthedeviceshouldbeconnectedtothenegativenodeofVOUTcapacitor.Thetrace　fromtheseresistorstotheVFBpinshouldbeshortandthin.Placeonthecomponentsideandavoidvia(s)betweentheseresistorsandthedevice.

ConnecttheovercurrentsettingresistorsfromTRIPpintogroundandmaketheconnectionsascloseaspossibletothedevice.ThetracefromTRIPpintoresistorandfromresistortogroundshouldavoidcouplingtoahigh-voltageswitchingnode.

ConnectthefrequencysettingresistorfromRFpintoground,ortothePGOODpin,andmaketheconnectionsascloseaspossibletothedevice.ThetracefromtheRFpintotheresistorandfromtheresistortogroundshouldavoidcouplingtoahigh-voltageswitchingnode.

Connectionsfromgatedriverstotherespectivegateofthehigh-sideorthelow-sideMOSFETshouldbeasshortaspossibletoreducestrayinductance.Use0.65mm(25mils)orwidertrace　andvia(s)ofatleast0.5mm(20mils)diameteralongthistrace.

ThePCBtracedefinedasswitchnode,whichconnectstosourceofhigh-sideMOSFET,drainoflow-sideMOSFETandhigh-voltagesideoftheinductor,shouldbeasshortandwideaspossible.

LAYOUTCONSIDERATIONSTOREMOTESENSING

VIN

TRIP2RF5TPS51218V5IN610mFDRVL450.1mF100WVTT_SENSE

ThermalPadGNDVSS_SENSEVOUT

VFBUDG-09067

Figure20.RemoteSensingofOutputVoltageUsingtheTPS51218

•••

MakeaKelvinconnectiontotheloaddevice.

Runthefeedbacksignalsasadifferentialpairtothedevice.Thedistanceoftheseparallelpairshouldbeasshortaspossible.

Runthelinesinaquietlayer.Isolatethemfromnoisysignalsbyavoltageorgroundplane.

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TPS51218APPLICATIONCIRCUITS

V5IN4.5Vto6.5VR15.6kWR6100kW12345R210kWR530kW(A)U1TPS51218PGOODTRIPENVFBRFVBST10DRVHSWV5INDRVL9876R70WC10.1mFQ1FDMS8680C310mFx4VIN8Vto20V

R31kWEN

L10.45mHVOUT1.1V18A

Q2FDMS8670ASC210mFQ3FDMS8670ASGNDC4330mFx4VOUT_GNDR4470kWUDG-09068

Figure21.1.1-V/18-AAuto-SkipMode

V5IN4.5Vto6.5VR15.6kWR6100kW1R31kWEN

R4(A)470kW2345R210kWR530kWU1TPS51218PGOODTRIPENVFBRFVBST10DRVHSWV5INDRVL9876Q2FDMS8670ASC210mFQ3FDMS8670ASR70WC10.1mFQ1FDMS8680C310mFx4VIN8Vto20V

L10.45mHVOUT1.1V18A

GNDC4330mFx4VOUT_GNDUDG-09069A.SeeTable1forresistor/frequencyvalues.

Figure22.1.1-V/18-AForcedContinuousConductionModeTable2.1.1-V,18-A,290-kHzApplicationListofMaterials

REFERENCEDESIGNATORC3C4L1Q1Q2,Q3

QTY11112

SPECIFICATION

4×10µF,25V4×330µF,2V,12mΩ0.45µH,25A,1.1mΩ30V,35A,8.5mΩ30V,42A,3.5mΩ

MANUFACTURERTaiyoYudenPanasonicPanasonicFairchildFairchild

PARTNUMBERTMK325BJ106MMEEFCX0D331XRETQP4LR45XFCFDMS8680FDMS8670AS

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PACKAGEMATERIALSINFORMATION

www.ti.com

19-May-2009

TAPEANDREELINFORMATION

*Alldimensionsarenominal

Device

PackagePackagePinsTypeDrawingSON

DSC

SPQ

ReelReelDiameterWidth(mm)W1(mm)330.0

12.4

A0(mm)B0(mm)K0(mm)

P1(mm)8.0

WPin1(mm)Quadrant12.0

TPS51218DSCR30003.33.31.1

PackMaterials-Page1

PACKAGEMATERIALSINFORMATION

www.ti.com

19-May-2009

*Alldimensionsarenominal

DeviceTPS51218DSCR

PackageType

SON

PackageDrawing

DSC

Pins10

SPQ3000

Length(mm)

346.0

Width(mm)346.0

Height(mm)

29.0

PackMaterials-Page2

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