LT3071EUFD datasheet(17/28 Pages) LINER

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LT3071

3071f

ApplicAtions inFormAtion

Figure 2. VIOC Control Block Diagram

PWRGD—Power Good

PWRGDpinisanopen-drainNMOSdigitaloutputthat

activelypullslowifanyoneofthesefaultmodesisde-

tected:

• VOUTislessthan90%ofVOUT(NOMINAL)ontherising

edgeofVOUT.

• VOUTdropsbelow85%ofVOUT(NOMINAL)formorethan

25µs.

• VBIASislessthanitsundervoltagelockoutthreshold.

• TheOUT-to-INreverse-currentdetectoractivates.

• Junctiontemperatureexceeds145°Ctypically.*

*Thejunctiontemperaturedetectorisanearlywarning

indicatorthattripsapproximately20°Cbeforethermal

shutdownengages.

Stability and Output Capacitance

TheLT3071’sfeedbacklooprequiresanoutputcapacitor

forstability.ChooseCOUTcarefullyandmountitinclose

proximitytotheLT3071’sOUTandGNDpins.Includewide

routingplanesforOUTandGNDtominimizeinductance.

Ifpossible,mounttheregulatorimmediatelyadjacentto

theapplicationloadtominimizedistributedinductance

for optimal load transient performance. Point-of-Load

applications present the best case layout scenario for

extractingfullLT3071performance.

LowESR,X5RorX7Rceramicchipcapacitorsarethe

LTCrecommendedchoiceforstabilizingtheLT3071.Ad-

ditionalbulkcapacitorsdistributedbeyondtheimmediate

decouplingcapacitorsareacceptableastheirparasiticESL

andESR,combinedwiththedistributedPCBinductance

isolatesthemfromtheprimarycompensationpoleprovided

bythelocalsurfacemountceramiccapacitors.

TheLT3071requiresaminimumoutputcapacitanceof

15µFforstability.LTCstronglyrecommendsthattheoutput

capacitornetworkconsistofseverallowvalueceramic

capacitorsinparallel.

Why Do Multiple, Small-Value Output Capacitors

Connected in Parallel Work Better?

TheLT3071’sunity-gainbandwidthwithCOUTof15µFis

about1MHzatitsfull-loadcurrentof5A.Surfacemounted

MLCC capacitors have a self-resonance frequency of

fR=1/(2π√LC),whichmustbepushedtoafrequencyhigher

thantheregulatorbandwidth.StandardMLCCcapacitors

areacceptable.Tokeeptheresonantfrequencygreater

than1MHz,theproduct1/(2π√LC)mustbegreaterthan

1MHz.Atthisbandwidth,PCBviascanaddsignificant

inductance,thusthefundamentaldecouplingcapacitors

mustbemountedonthesameplaneastheLT3071.

REFERENCE

LT3071

VREF

VOUT +

300mV

OUT

VIOC

3071 F02

LOAD

–

PWM

SWITCHING REGULATOR

REF

ITH

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