Automotive Electronic Systems Drive the Demand for Multi ...P354, EN Automotive Electronic Systems...
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P354, EN Automotive Electronic Systems Drive the Demand for Multi-Channel Synchronous Buck Converters By Jeff Gruetter Product Marketing Manager Linear Technology Corporation Introduction As automobiles continue to add a higher density of electronic systems to enhance safety, comfort, efficiency and performance, it is not surprising that they require both smaller and higher performance power conversion solutions. These new multi-channel power management solutions need to deliver up to four independent power rails usually to power V CORE ,V I/O ,V MEM required for microprocessors and generally a fourth 5V rail to power a CAN transceiver. According to Strategy Analytics, “The demand for enabling semiconductor devices is expected to grow at a compound average annual growth rate (CAGR) of five percent over the next seven years, with the total market worth over $41 billion by 2021, compared to $30 billion in 2014.” They also identified that demand for microcontroller and power semiconductors will drive over 40 percent of revenues.
Transcript of Automotive Electronic Systems Drive the Demand for Multi ...P354, EN Automotive Electronic Systems...
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P354, EN
AutomotiveElectronicSystemsDrivetheDemandforMulti-ChannelSynchronousBuckConverters
ByJeffGruetter
ProductMarketingManagerLinearTechnologyCorporation
IntroductionAsautomobilescontinuetoaddahigherdensityofelectronicsystemstoenhancesafety,comfort,efficiencyandperformance,itisnotsurprisingthattheyrequirebothsmallerandhigherperformancepowerconversionsolutions.Thesenewmulti-channelpowermanagementsolutionsneedtodeliveruptofourindependentpowerrailsusuallytopowerVCORE,VI/O,VMEMrequiredformicroprocessorsandgenerallyafourth5VrailtopoweraCANtransceiver.AccordingtoStrategyAnalytics,“Thedemandforenablingsemiconductordevicesisexpectedtogrowatacompoundaverageannualgrowthrate(CAGR)offivepercentoverthenextsevenyears,withthetotalmarketworthover$41billionby2021,comparedto$30billionin2014.”Theyalsoidentifiedthatdemandformicrocontrollerandpowersemiconductorswilldriveover40percentofrevenues.
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StrategyAnalyticsprovidesaveryquantitativedescriptionofforecastingthegrowthofelectronicscontentinautomobiles,butmoreinterestingistheprevalentrolethatpowerICsplayinthisgrowth.ThesenewpowerICsmustprovide:
1) MultiplevoltagerailsfromasinglepowermanagementIC2) Robustperformanceacrossawiderangeofvoltages,includingcold-crankandstop-
startscenariosfrom
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independentoutputstopowerVCORE,VI/O,VMEMrequiredformicroprocessorsandafourth5VrailtopoweraCANtransceiverwhichenablesthemicroprocessortocommunicatewiththerestofthesystemelectronics.BecauseaproperlydesignedquadconverterICisonlymoderatelylargerthananequivalentsingleconverterwhereasitssolutionfootprintcanbelessthanhalfthesizeoffourseparatesingleconverters.Thissizeimprovementisespeciallycompellingwhencomparingaquadoutputregulatorusingaswitchingfrequencyof2MHzversusfoursingleswhichrunat500KHz.Additionally,quadoutputconvertersaredesignedtominimizeunwantedcross-talkbetweenthechannels,whereascrosstalkbetweenfouradjacentsingleconverterscanbeproblematic,unlesstheyareallsynchronizedtoacommonclock.Addinganexternalclockandsynchronizationaddsbothsize,complexityandcosttothecircuit.LowEMIOperationBecausetheautomotiveelectricalenvironmentisinherentlynoisy,withmanyapplicationsbeingsusceptibletoelectromagneticinterference(EMI),itisimperativethatswitchingregulatorsdon’texacerbatetheseEMIconcerns.Becauseaswitchingregulatoristypicallythefirstactivecomponentontheinputpowerbusline,andregardlessofdownstreamconverters,itsignificantlyimpactsoverallconverterEMIperformance.SominimizingEMIisimperative.Historically,thesolutionwastouseanEMIshieldingbox,butthisaddssignificantcostandsizetothesolutionfootprintwhilecomplicatingthermalmanagement,testingandmanufacturability.AnotherpotentialsolutionwithinthepowermanagementICistoslowdowntheswitchingedgesoftheinternalMOSFETs.However,thishastheundesiredeffectofreducingtheefficiencyandincreasingtheminimumon-timewhichcompromisestheIC’sabilitytodeliverlowdutycyclesatswitchingfrequenciesat,orabove,2MHz.Asbothhighefficiencyandsmallsolutionfootprintsaredesired,thisisn’taviablesolution.Fortunately,somerecentpowerICdesignshavebeenintroducedtoenablefastswitchingfrequencies,highefficiencyoperationandlowminimumon-timesconcurrently.ThesedesignscanofferlowEMIemissionsevenwith2MHzswitchingfrequenciesandover90%efficiency.Theseperformancelevelsareaccomplishedwithnoadditionalcomponentsorshielding,offeringasignificantbreakthroughinswitchingregulatordesign. ANewAlternativeLinearTechnology’sLT8602isa42Vvoltinputcapable,highefficiency,quadoutputmonolithicsynchronousstep-downswitchingregulator.Its3Vto42Vinputvoltagerangemakeitidealforautomotiveapplicationswhichmustregulatethroughcold-crankandstop-startscenarioswithminimuminputvoltagesaslowas3Vandloaddumptransientsinexcessof40V.Ascanbeseeninfigure1,itsquadchanneldesigncombinestwohighvoltage2.5Aand1.5Achannelswithtwolowervoltage1.8Achannelstodeliverfourindependentoutputsdeliveringvoltagesaslowas0.8Venablingittodrivethelowestvoltagemicroprocessorcorescurrentlyavailable.Itssynchronousrectificationtopologydeliversupto94%efficiencywhileBurstMode®operationkeepsquiescentcurrentunder30µA(allchannelson)inno-loadstandbyconditionsmakingitidealforalways-onsystems.
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Figure1.LT8602SchematicDelivering5V,3.3V,1.8V&1.2VOutputs Fornoisesensitiveapplications,theLT8602,withasmallexternalfilter,canutilizeitspulse-skippingmodetominimizeswitchingnoiseandcanmeettheCISPR25,Class5EMIrequirementsasshowninFigure2.
Figure2.LT8602RadiatedEMIPerformance,
(CISPR25RadiatedEmissionTestswithClass5PeakLimit)
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TheLT8602’sswitchingfrequencycanbeprogrammedfrom250kHzto2MHzandcanbesynchronizedthroughoutthisrange.Its60nsminimumon-timeenables16VINto2.0VOUTstep-downconversionsonthehighvoltagechannelswitha2MHzswitchingfrequency.AsthehighvoltageVOUT2channelfeedsthetwolowvoltagechannels(VOUT3andVOUT4),thesecandeliveroutputsaslowas0.8Vwhilealsoswitchingat2MHz,offeringaverycompact(~25mmx25mm)quadoutputsolutionasshowninFigure3.
Figure3.LT8602QuadOutputSolutionFootprint(2xactualsize)
Inadditiontheminimizingthesolutionfootprint,theLT8602’s2MHzswitchingfrequencyenablesdesignerstoavoidcriticalnoise-sensitivefrequencybands,suchasAMradio.EachchanneloftheLT8602maintainsaminimumdropoutvoltageofonly200mV(@1A)underallconditions,enablingittoexcelinscenariossuchasautomotivecold-crank.Programmablepower-onresetandpowergoodindicatorsforeachchannelhelpstoensureoverallsystemreliability.TheLT8602’s40-leadthermallyenhanced6mmx6mmQFNpackageandhighswitchingfrequencykeepsexternalinductorsandcapacitorssmall,providingacompact,thermallyefficientfootprint.TheLT8602utilizesquadinternaltopandbottomhighefficiencypowerswitcheswithallthenecessaryboostdiodes,oscillator,controlandlogiccircuitryintegratedontoasingledie.Channel1and3switch180degoutofphasewithchannel2and4toreduceoutputripple.Eachchannelhasaseparateinputforaddeddesignflexibility,butmostapplicationswillrunthetwolowvoltagechannelsdirectlyfromthetwohighvoltagechannelstoofferaverysimple,highfrequencyquadoutputdesign.LowrippleBurstMode®operationmaintainshighefficiencyatlowoutputcurrentswhilekeepingoutputripplebelow15mVPK-PK.UniquedesigntechniquesandanewhighspeedprocessenablehighefficiencyoverawideinputvoltagerangeandtheLT8602’scurrent-modetopologyenablesfasttransientresponseandexcellentloopstability.Otherfeaturesincludeinternalcompensation,apowergoodflags,outputsoftstart/tracking,short-circuitandthermalprotection.
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ConclusionTherapidincreaseinthenumberandcomplexityofelectronicsystemsinautomobileshasnecessitatedevenhigherdemandsonpowermanagementICperformance.ByhavingquadoutputpowerICs,automotivedesignerscandramaticallyreducethespacerequiredbytheirpowerconversioncircuits.Combinedwithswitchingfrequenciesof2MHz,thesizeoftheexternalcomponents,namelytheinductorsandoutputcapacitors,canalsobedramaticallyreducedofferingaverycompactquadrailsolutionfootprint.Thesecompactdesignsarealsoveryrugged,capabletowithstandtherequiredtransientbehaviorfoundinstop-start,cold-crankandload-dumpconditionswhileaccuratelyregulatingalloutputs.Additionally,ultralowquiescentcurrentsmakethemidealforalwaysonsystems.Asmoreelectronicsystemsareaddedintoevershrinkingspaces,minimizingthesolutionfootprintwhilemaximizingefficiencyisalsocritical.Fortunatelyanewgenerationofmulti-outputpower ICswhichmeetthesedemandsarealreadyavailablepavingthewayforevenhigherelectroniccontentinfuturevehicles.
