LT3071EUFD datasheet(11/28 Pages) LINER

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LT3071

3071f

pin Functions

VIOC (Pin 1):VoltageforIn-to-OutControl.TheICin-

corporatesauniquetrackingfunctiontocontrolabuck

regulatorpoweringtheLT3071’sinput.TheVIOCpinis

theoutputofthistrackingfunctionthatdrivesthebuck

regulatortomaintaintheLT3071’sinputvoltageatVOUT+

300mV.Thisfunctionmaximizesefficiencyandminimizes

powerdissipation.SeetheApplicationsInformationsec-

tionformoreinformationonpropercontrolofthebuck

regulator.

PWRGD (Pin 2):PowerGood.ThePWRGDpinisanopen-

drainNMOSoutputthatactivelypullslowifanyoneof

thesefaultmodesisdetected:

• VOUTislessthan90%ofVOUT(NOMINAL)ontherising

edgeofVOUT.

• VOUTdropsbelow85%ofVOUT(NOMINAL)formorethan

25µs.

• Junctiontemperaturetypicallyexceeds145°C.

• VBIASislessthanitsundervoltagelockoutthreshold.

• TheOUT-to-INreverse-currentdetectoractivates.

SeetheApplicationsInformationsectionformoreinfor-

mationonPWRGDfaultmodes.

REF/BYP (Pin 3):ReferenceFilter.Thepinistheoutput

ofthebandgapreferenceandhasanimpedanceofap-

proximately19kΩ.Thispinmustnotbeexternallyloaded.

BypassingtheREF/BYPpintoGNDwitha10nFcapacitor

decreasesoutputvoltagenoiseandprovidesasoft-start

functiontothereference.LTCrecommendstheuseofa

highquality,lowleakagecapacitor.SeetheApplications

Informationsectionformoreinformationonnoiseand

outputvoltagemarginingconsiderations.

GND (Pins 4, 9-14, 20, 26, Exposed Pad Pin 29):Ground.

TheexposedpadoftheQFNpackageisanelectricalcon-

nectiontoGND.Toensureproperelectricalandthermal

performance,solderPin29tothePCBgroundandtieto

allGNDpinsofthepackage.TheseGNDpinsarefused

totheinternaldieattachpaddleandtheexposedpadto

optimizeheatsinkingandthermalresistancecharacteris-

tics.SeetheApplicationsInformationsectionforthermal

considerationsandcalculatingjunctiontemperature.

IN (Pins 5, 6, 7, 8): Input Supply. These pins supply

powertothehighcurrentpasstransistor.TieallINpins

togetherforproperperformance.TheLT3071requiresa

bypasscapacitoratINtomaintainstabilityandlowinput

impedanceoverfrequency.A47µFinputbypasscapacitor

sufficesformostbatteryandpowerplaneimpedances.

Minimizinginputtraceinductanceoptimizesperformance.

ApplicationsthatoperatewithlowVIN-VOUTdifferential

voltagesandthathavelarge,fastloadtransientsmayrequire

muchhigherinputcapacitorrequirementstopreventthe

inputsupplyfromdroopingandallowingtheregulatorto

enterdropout.SeetheApplicationsInformationsection

formoreinformationoninputcapacitorrequirements.

OUT (Pins 15, 16, 17, 18):Output.Thesepinssupply

powertotheload.TieallOUTpinstogetherforproper

performance.Aminimumoutputcapacitanceof15µFis

requiredforstability.LTCrecommendslowESR,X5Ror

X7Rdielectricceramiccapacitorsforbestperformance.

Aparallelceramiccapacitorcombinationof10µF+4.7µF

+2.2µFor151µFceramiccapacitorsinparallelprovide

excellentstabilityandloadtransientresponse.Largeload

transientapplicationsrequirelargeroutputcapacitorsto

limitpeakvoltagetransients.SeetheApplicationsInfor-

mationsectionformoreinformationonoutputcapacitor

requirements.

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