LT3071EUFD datasheet(14/28 Pages) LINER

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LT3071

3071f

ApplicAtions inFormAtion

Introduction

Current generation FPGA and ASIC processors place

stringentdemandsonthepowersuppliesthatpowerthe

core,I/Oandtransceiverchannels.Thesemicroprocessors

maycycleloadcurrentfromnearzerotoampsintensof

nanoseconds.Outputvoltagespecifications,especiallyin

the1Vrange,requiretighttolerancesincludingtransient

responseaspartoftherequirement.SomeASICprocessors

requireonlyasingleoutputvoltagefromwhichthecore

andI/Ocircuitryoperate.SomehighperformanceFPGA

processorsrequireseparatepowersupplyvoltagesforthe

processorcore,theI/O,andthetransceivers.Often,these

supplyvoltagesmustbelownoiseandhighbandwidth

toachievethelowestbit-errorrates.Theserequirements

mandatetheneedforveryaccurate,lownoise,highcur-

rent,veryhighspeedregulatorcircuitsthatoperateatlow

inputandoutputvoltages.

TheLT3071isalowvoltage,UltraFasttransientresponse

linearregulator.Thedevicesuppliesupto5Aofoutput

currentwithatypicaldropoutvoltageof85mV.A0.01µF

referencebypasscapacitordecreasesoutputvoltagenoise

to25µVRMS(BW=10Hzto100kHz).TheLT3071’shigh

bandwidthprovidesUltraFasttransientresponseusinglow

ESRceramicoutputcapacitors(15µFminimum),saving

bulkcapacitance,PCBareaandcost.

TheLT3071’sfeaturespermit

state-of-the-artlinearregula-

torperformance.TheLT3071isidealforhighperformance

FPGAs,microprocessors,sensitivecommunicationsup-

plies,andhighcurrentlogicapplicationsthatalsooperate

overlowinputandoutputvoltages.

Output voltage for the LT3071 is digitally selectable in

50mVincrementsovera0.8Vto1.8Vrange.Ananalog

marginingfunctionallowstheusertoadjustsystemoutput

voltageoveracontinuous±10%range.

The LT3071 provides an output current monitor that

typically sources a current of IOUT/2500or400µAper

ampofIOUTatitsIMONpin.TerminatingtheIMONpinto

GNDwitharesistorproducesavoltageproportionalto

outputcurrent.Thispermitsausertomeasuresystem

performancesuchasoutputpowerorifoutputcurrent

exceedsorfallsbelowsomethreshold.

TheICincorporatesauniquetrackingfunction,whichif

enabledbytheuser,controlsanupsteamregulatorpower-

ingtheLT3071’sinput(seeFigure8).Thistrackingfunction

drivesthebuckregulatortomaintaintheLT3071’sinput

voltageto VOUT+300mV.Thisinput-to-outputvoltage

controlallowstheusertochangetheregulatoroutput

voltage,andhavetheswitchingregulatorpoweringthe

LT3071’sinputtotracktotheoptimuminputvoltagewith

nocomponentchanges.

This combines the efficiency of a switching regulator

withsuperiorlinearregulatorresponse.Italsopermits

thermalmanagementofthesystemevenwithamaximum

5Aoutputload.

LT3071internalprotectionincludesinputundervoltage

lockout(UVLO),reverse-currentprotection,precisioncur-

rentlimitingwithpowerfoldbackandthermalshutdown.

TheLT3071regulatorisavailableinathermallyenhanced

28-lead,4mm

×5mmQFNpackage.

TheLT3071’sarchitecturedrivesaninternalN-channel

powerMOSFETasasourcefollower.Thisconfiguration

permitsausertoobtainanextremelylowdropout,Ultra-

Fasttransientresponseregulatorwithexcellenthighfre-

quencyPSRRperformance.TheLT3071achievessuperior

regulatorbandwidthandtransientloadperformanceby

eliminatingexpensivebulktantalumorelectrolyticcapaci-

torsinthemostmodernanddemandingmicroprocessor

applications.Usersrealizesignificantcostsavingsasall

additional bulk capacitance is removed. The additional

savingsofinsertioncost,purchasing/inventorycostand

boardspacearereadilyapparent.Precisionincremental

outputvoltagecontrolaccommodateslegacyandfuture

microprocessorpowersupplyvoltages.

Outputcapacitornetworkssimplifytodirectparallelcom-

binationsofceramiccapacitors.Often,thehighfrequency

ceramicdecouplingcapacitorsrequiredbythesevarious

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