P365, EN
PlaceDC/DCRegulatorsonBacksideofPCBtoClearRoomontheTopsideforDigitalICs
By Afshin Odabaee, Power Module Business Manager Sam Young, Applications Engineer
Linear Technology
FasterIC-to-ICdatacommunicationbenefitsusallwithmorecapablesystemsfromhigherqualityvideostreamingtomorecapablenetworkingequipment.ThisflowofmoredatainshortertimeperiodsexertspressureonsystemdesignerstotackletheeverlastingchallengeofdataqualitybyminimizingunintendedinducederrorsespeciallythosestemmingfromPCBlayouts,traceimped-ance,crosstalk,EMIandotherfactors.So,itmakessensetoshortendistancesbetweenICthatareinconstantcommunicationwitheachotherandaddmorelayerstothePCBwhichconstituteadensercircuitboards.Doingsostartsanotherbattle:thefighttofitasmanyICsandconnectorsontopofPCBwithoutincreasingthecostoftheend-product.Thecostisinlargepercentageassoci-atedwiththesizeandthicknessofthePCB.ForsmallersizeboardsandfewerPCBlayers,some-timesthequestionbecomeswhichcomponentsneedtoberemovedorwhichfunctionsmustbeeliminatedtoreducethemanufacturingcostalbeit,theresalevalueofthedevicemaybeinjeop-ardy.It’safighttofitperformanceandfeatures.
ThetopsideofsystemboardssuchasPCIecardsaredenselypopulatedwithFPGA/ASIC/µP,transceivers,connectors,memoryICsandDC/DCregulatorcircuitsofvariousheightsuptoafewcentimeters.However,thebacksideoftenhasaheightrestrictionwhereonlycomponentswithlessthan2.3mmtallpackagessuchascapacitorsareallowedandmuchofrealestateisunoccu-pied.Whatifthisempty PCBareacouldbeusedbyDC/DCregulatorcircuitsunclutteringthetopsideallowinguseofmorememoryICs,forexample,addingtothesystem’scapability?ThetopsideofsystemboardssuchasPCIecardsaredenselypopulatedwithFPGA/ASIC/uP,transceivers,connectors,memoryICsandDC/DCregulatorcircuitsofvariousheightsuptoafewcentimeters.However,thebacksideoftenhasaheightrestrictionwhereonlycomponentswithlessthan2.3mmtallpackagessuchascapacitorsareallowedandmuchofrealestateisunoccupuied.WhatifthisemptyPCBareacouldbeusedbyDC/DCregulatorcircuitsunclutteringthetopsideallowinguseofmorememoryICs,forexample,addingtothesystem’scapability?
TheLTM4622isadual2.5Aorbytyingtheoutputsincurrentsharing,single5A,step-downµModule®(powermodule)regulatorin6.25mm×6.25mm×1.82mmultrathinLGApackage.Atnearlytheheightofasoldereddown0805casesizecapacitor,itsultralowheightallowsittobemountedonthebacksideofaPCB,freeingspaceonthetopsidefordigitalICs.Thethinprofileallowsittomeetdemandingheightre-strictionssuchasthoserequiredbyPCIeandAdvancedMezzanineCardsinembeddedcomputingsystems.
Figure1.LTM4622TinyDualSupplyinUltrathinPackage
MirroredLayoutforHigherPower,SmallerPCB
TheLTM4622’spinconfigurationisorganizedsymmetrically,soforhighercurrentapplicationswheretwoLTM4622scanbeparallel,onedevicecanbeonthetopsideofPCBandtheothermirroredonthebottomside,minimizingPCBareawhileincreasingoutputpowerandpowerdensity.
Flexible Dual Supply in a Simple < 0.5cm2 Footprint
TheLTM4622hasawideinputvoltagerangeof3.6Vto20V,idealanditcanalsobeconfiguredtooperatedownto3.1Vforoperationfroma3.3Vinputsupply.Itregulatestwovoltagesforacompactmulti-railsolu-tionwhereeachoutputcansupplyupto2.5A(3Apeak)andiscapableofpreciselyregulatingbetween0.6Vto5.5Vtowith1.5%maximumtotalDCoutputvoltageerroroverline,loadandtemperature.Forhigheroutputcurrentupto5A,simplytietheoutputsforcurrentsharing.
TheLTM4622requiresonly3ceramiccapacitorsand2resistorstocompleteasolutionoccupyinglessthan1cm2
single-sidedor0.5cm2onadouble-sidedPCB.
Figure2showstheLTM4622circuitinatypicaldualoutputapplication,alsoillustratingitscompactsolutionsize.Efficiencyandpowerlossforthecircuitoperatingata12VinputareshowninFigure3.
Figure2.TypicalApplication:1.5V/2.5A,1.2V/2.5ADual
Figure3.Efficiency,Lossat12VInput(Fig.2)
Reliable High Performance Regulation
TheLTM4622hasacontrolledon-timecurrent-modearchitectureforafasttransientwithgoodloopstabil-ityoverawidevoltagerange.Itprovidessystemprotectionsuchasshort-circuit,overvoltageandover-temperatureaswellasensuresmonotonicoutputvoltagerampingwithtracking,soft-startandtheabilitytostartintoapre-biasedoutput.Italsohasnolimitationoninputsupplyslewrate.
Figures4and5demonstratethefasttransientandpre-biasstart-upperformancesforthe1.5VoutputrailofFigure2circuit.
Figure4.12VIN,1.5VOUT1.25A-2.5ALoadStep(Fig.2)
Figure5.12VIN,1.8VOUTStart-upintoPre-BiasedOutput
ParallelOperationforHigherCurrentApplicationsTheLTM4622’scurrent-modearchitecturegivesitgoodandreliablecycle-by-cyclecurrentmonitoringal-lowingforitsoutputstobeparalleledtogethertosupportloadcurrentsofupto5A.
Figures6and7demonstratethegoodthermalandcurrentsharingperformanceoftheLTM4622whileconfiguredforatwooutputscurrentsharing,generatinga3.3Vat5Afroma5Vinput.
Figure6.VIN=5V,VOUT=3.3V/5A,TA=25CThermals
Figure7.VIN=5V,VOUT=3.3V/5ACurrentSharing
ConclusionTheultrathinLTM4622providesahighperformanceregulatorforsingleandmulti-railapplications.Itswideoperatingrange,featuresandcompactsolutionsizemakeitahighlyflexibleandrobustsolutioncapableoffittingintothetightestspacesontopsideandbacksideofaPCB.
Top Related