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P395, EN
PowerSupplySequencingSimplifiedByNathanEnger,SeniorApplicationsEngineer,MixedSignalProducts,LinearTechnologyCorp.
Thechallengesindesigningamultiplepowersupplymultiplywitheachadditionalsupplyrail.Thedesignermustconsiderthedynamicenvironmentofcoordinatedpowersupplysequencingandtiming,generatingpower-onreset,monitoringforfaultsandrespondingappropriatelytoprotectthesystem.Anexperienceddesignerrecognizesthatflexibilityiskeytosuccessfullynavigatingtheebbandflowasaprojectmovesfromprototypetoproduction.Theidealsolutionminimizesthenumberofhardwareandsoftwarechangesduringdevelopment.
TheidealmultisupplydesigntoolisasingleICthatresidesinadesignfrombeginningtoend,requiringnowiringchangesthroughthelifecycleoftheproduct.Itautonomouslysupervisesandsequencesmultiplepowerrails,cooperatingwithotherICstoseamlesslysupervisemanypowerregulatorsinthesystem,andprovidesfaultandresetmanagement.ThedesignercanusepowerfulPC-basedsoftwaretoconfigure,visualizeanddebugsystembehaviorinrealtimewhenconnectedtoanI2Cbus.
TheLTC2937fitsthisbill.Itisa6-channelvoltagesequencerandhighaccuracysupervisorwithEEPROM.Eachofthesixchannelshastwodedicatedcomparatorstoaccuratelymonitorover-andundervoltageconditionstowithin±0.75%.Thecomparatorthresholdsareindividuallyprogrammableoverarangeof0.2Vto6Vwith8-bitresolution.Thecomparatorsarefast,withdeglitchedpropagationdelaysof10μs.Eachsequencerchannelhasanenableoutputthatcancontrolanexternalregulator,orthegateofapassFET.Allaspectsofsupervisorvoltageandsequencertimingareindividuallyconfigurable,includingup-anddown-sequenceorder,sequencetimingparameters,andfaultresponse.Thebuilt-inEEPROMmakesthepartcompletelyautonomousandabletopower-upinthecorrectstatetocontrolthesystem.Inaddition,multipleLTC2937scancooperatetoautonomouslysequenceupto300suppliesinasystem,allusingasingle-wirecommunicationbus.
Powersupplyfaultsarecontrollable,visibleandmanageablethroughtheLTC2937’sautonomousfaultresponsebehaviors,andthroughdebugregisters.TheLTC2937automaticallydetectsfaultconditionsandcanpowerdownthesysteminacoordinatedmanner.Itcanremainoff,orattempttoresequencethesuppliesafterthefault.InasystemwithamicrocontrollerandanI2C/SMBus,theLTC2937providesdetailedinformationregardingthetypeandcauseofthefault,andthestateofthesystem.Themicrocontrollercanmakedecisionsabouthowtorespond,orallowtheLTC2937torespondonitsown.
Figure1.LTC2937sequencingsixsupplies
THREESTEPSOFPOWERSUPPLYCONTROL
Apowersupplycyclehasthreeoperatingsteps:sequence-up,monitoringandsequence-down.Figure2showsthesephasesforatypicalsystem.Duringup-sequencing,eachpowersupplymustwaititsturn,andthenpoweruptothecorrectvoltageinadesignatedamountoftime.Duringthemonitoringphaseeachpowersupplymustremainwithindesignatedover-andundervoltagelimits.Duringdown-sequencing,eachsupplymustwaititsturn(ofteninadifferentorderfromup-sequencing),thenpowerdownwithinaconfiguredtimelimit.Atanypoint,somethingcangowrong,causingafaultinthesystem.Thedesignchallengeistocreateasysteminwhichallofthesesteps,andallofthevariables,areeasilyconfigurable,butcarefullycontrolled.
Figure2.Powersupplysequencingwaveforms
Sequence-upbeginswhentheONinputtransitionstoactive.TheLTC2937advancesthroughitsup-sequence,enablingeachsupplyinturn,andmonitoringtoensurethatthesupplyvoltagerisesabovetheconfiguredthresholdbeforetheconfiguredtime.Anysupplythatfailstomeetitsassignedtimingtriggersasequencingfault.
AuniquebenefitoftheLTC2937isitssequencepositionclock.Eachchannelisassignedtoasequenceposition(1–1023),andreceivesitsenablesignalwhentheLTC2937countstothegivennumberinthesequence.Achannelwithsequenceposition1isalwaysenabledbeforeachannelwithsequenceposition2.Ifasystemspecificationchanges,requiringthesetwochannelstosequenceinadifferentorder,thenthesequencepositionscanbeswapped,poweringthesecondchannelinsequenceposition1,andthefirstinposition2.MultipleLTC2937scansharesequencepositioninformation,sothatsequencepositionNhappensatthesametimeforallLTC2937chips,andchannelscontrolledbydifferentchipscanparticipateinthesamesequence(seeFigure3).
Figure3.TypicalconnectionsbetweenmultipleLTC2937s
Themonitoringphasebeginswhenthelastchannelsequencesupandcrossesitsundervoltagethreshold.Duringmonitoring,theLTC2937usesitshighaccuracycomparatorstocontinuouslymonitorthevoltageateachinputagainstover-andundervoltagethresholds.Itignoresminorglitchesontheinputs,onlytriggeringifthevoltagecrossesthethresholdwithsufficientmagnitudeforsufficienttime.WhentheLTC2937detectsafault,itrespondsimmediatelyaccordingtoitsconfiguredsupervisorfaultresponse.Inatypicalscenario,itshutsdownallsuppliessimultaneously,assertingRESETBtothesystem,thenitattemptstoresequenceupaccordingtothenormalstart-upsequence.Thispreventsthesuppliesfrompoweringpartsofthesystemwhileothersareunpowered,orexecutinganuncoordinatedrecoveryafterthefault.MultipleLTC2937sinasystemcansharefaultstate,andrespondtoeachother’sfaults,maintainingcompletecoherencebetweencooperatingchannelsduringfaultrecovery.TheLTC2937offersnumerousprogrammablefaultresponsebehaviorstosatisfymanydifferentsystemconfigurations.
Thesequence-downphasebeginswhentheONinputtransitionslow.Thesequencepositionclockbeginsitscountagaintobringthesuppliesdown,butallofthesequence-downparametersareindependentfromthesequence-upparameters.Channelscansequencedowninanyorder,andmultipleLTC2937chipscoordinatesequencingofallcontrolledsupplies.Duringthedown-sequence,eachsupplymustfallbelowitsdischargethresholdwithinitsconfiguredtimelimit,ortriggerasequencingfault.TheLTC2937canpulldownonthesupplywithanoptionalcurrentsourcetoactivelydischargeslowmovingsupplies.
Thesequencepositionclockenforcesevent-basedsequenceorder,witheacheventwaitingforprecedingeventsbeforeitcancontinue.TheLTC2937alsoallowstime-basedsequencing,andcanparticipateinsystemsthatenablesupplyrailsatpredeterminedtimepoints.Reconfigurableregistersfunctionineithertime-basedorevent-basedmode.
LTpowerPlayMAKESITSIMPLE
TheLTC2937’sextensiveregistersetispowerful,yetmasteringitissimple.TheLTpowerPlaygraphicaluserinterface(GUI)displaysallofthestatusanddebugregisterinformationinoneconvenientinterface.TheGUIcommunicateswithanyLinearTechnologypowersystemmanagementIC(includingtheLTC2937)ontheI2C/SMBus.ConfiguringoneormoreLTC2937sisassimpleasafewclicksofthemouse.
LTpowerPlaysavessettingsonthePC,andcanwritethemintotheLTC2937EEPROM.TheGUIalsoshowsallofthedebuginformationforsystemmalfunctions.LTpowerPlaycanshowwhenanysupplyisover-orundervoltage,orifasupplyhasfailedsequencetiming.Afterafault,theGUIallowscompletecontroloverrestartingthesystem.Ineverystageofthedesign—start-up,configuration,debug,andoperation—LTpowerPlayisanindispensablewindowintosystemperformance.
Figure4.LTpowerPlaygraphicaluserinterface(GUI)displaysallofthestatusanddebugregisterinformationinoneconvenientinterface.ConfiguringoneormoreLTC2937sisassimpleasafewclicksofthemouse.LTpowerPlaysavessettingsonthePC,andcanwritethemintotheLTC2937EEPROM.
CONCLUSION
TheLTC2937simplifiespowersystemsequencingandsupervision.Itrequiresverylittleboardrealestateforacompletesystem.Itisflexibleandreconfigurable,yetautonomousthroughitsEEPROMmemory.Itcanoperateonitsown,orinconcertwithotherchipsinalargesystem,seamlesslyorchestratingtheoperationsofupto300powersupplies.n
Table1.Programmable6-channelsequencerandsupervisorswithEEPROM
LTC2933 LTC2936 LTC2937
Sequencer No No Yes
ComparatorOutputs
No Yes No
ThresholdRange
1Vto13.9V(1×)0.2Vto5.8V(5×)
0.2Vto5.8V(6×) 0.2Vto6V(6×)
ThresholdAccuracy
±1% ±1% ±0.75%
PowerSupply 3.4Vto13.9V 3.13Vto13.9V 2.9Vto16.5V
Package(mm×mm)
5×4DFN-16,SSOP-16
4×5QFN-24,SSOP-24 5×6QFN-28