LT3071EUFD datasheet(20/28 Pages) LINER

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LT3071

3071f

ApplicAtions inFormAtion

thefartherthewiresareplacedapartfromeachother,the

moreinductancewillbereduced,uptoa50%reduction

whenplacedafewinchesapart.Splittingthewiresbasi-

callyconnectstwoequalinductorsinparallel.However,

whenplacedincloseproximityfromeachother,mutual

inductanceisaddedtotheoverallselfinductanceofthe

wires.Themosteffectivewaytoreduceoverallinductance

istoplacetheforwardandreturn-currentconductors(the

wirefortheinputandthewireforthereturnground)in

very close proximity. Two 18-AWG wires separated by

0.05inchreducetheoverallselfinductancetoaboutone-

fourthofasingleisolatedwire.IftheLT3071ispowered

byabatterymountedincloseproximitywithgroundand

power planes on the same circuit board, a 47µF input

capacitorissufficientforstability.However,iftheLT3071

ispoweredbyadistantsupply,usealowESR,largevalue

inputcapacitorontheorderof330µF.Aspowersupply

outputimpedancevaries,theminimuminputcapacitance

neededforapplicationstabilityalsovaries.

Bias Pin Capacitance Requirements

TheBIASpinsuppliescurrenttomostoftheinternal

controlcircuitryandtheoutputstagedrivingthepass

transistor.TheLT3071requiresaminimum2.2µFby-

pass capacitor for stability and proper operation. To

ensure proper operation, the BIAS voltage must sat-

isfythefollowingconditions:2.2V≤VBIAS≤3.6Vand

VBIAS ≥ (1.25 • VOUT + 1V). For VOUT ≤ 0.95V, the

minimumBIASvoltageislimitedto2.2V.

Load Regulation

TheLT3071providesaKelvinsensepinforVOUT,allowing

theapplicationtocorrectforparasiticpackageandPCB

I-Rdrops.However,LTCrecommendsthattheSENSEpin

terminateincloseproximitytotheLT3071’sOUTpins.

Thisminimizesparasiticinductanceandoptimizesregula-

tion.TheLT3071handlesmoderatelevelsofoutputline

impedance,butexcessiveimpedancebetweenVOUTand

COUTcausesexcessivephaseshiftinthefeedbackloop

andadverselyaffectsstability.

Figure1inthePinFunctionssectionillustratestheKelvin-

Senseconnectionmethodthateliminatesvoltagedrops

duetoPCBtraceresistance.However,notethatthevoltage

dropacrosstheexternalPCBtracesaddstothedropout

voltageoftheregulator.TheSENSEpininputbiascurrent

dependsontheselectedoutputvoltage.SENSEpininput

currentvariesfrom50µAtypicallyatVOUT=0.8Vto300µA

typicallyatVOUT=1.8V.

Short-Circuit and Overload Recovery

LikemanyICpowerregulators,theLT3071hassafeop-

eratingarea(SOA)protection.Thesafeareaprotection

decreasescurrentlimitasinput-to-outputvoltageincreases

andkeepsthepowertransistorinsideasafeoperating

regionforallvaluesofinput-to-outputvoltageuptothe

absolutemaximumvoltagerating.VBIASmustbeabove

theUVLOthresholdforanyfunction.TheLT3071hasa

precisioncurrentlimitspecifiedat±20%thatisactiveif

VBIASisaboveUVLO.

Under conditions of maximum ILOAD and maximum

VIN-VOUTthedevice’spowerdissipationpeaksatabout

3W.Ifambienttemperatureishighenough,diejunction

temperaturewillexceedthe125°Cmaximumoperating

temperature. If this occurs, the LT3071 relies on two

additionalthermalsafetyfeatures.Atabout145°C,the

PWRGDoutputpulls

lowprovidinganearlywarningofan

impendingthermalshutdowncondition.At165°Ctypically,

theLT3071’sthermalshutdownengagesandtheoutputis

shutdownuntiltheICtemperaturefallsbelowthethermal

hysteresislimit.TheSOAprotectiondecreasescurrentlimit

astheIN-to-OUTvoltageincreasesandkeepsthepower

dissipationatsafelevelsforallvaluesofinput-to-output

voltage.TheLT3071providessomeoutputcurrentatall

valuesofinput-to-outputvoltageuptotheabsolutemaxi-

mumvoltagerating.SeetheCurrentLimitvsVINcurvein

theTypicalPerformanceCharacteristics.

Duringstart-up,aftertheBIASvoltagehascleareditsUVLO

thresholdandVINisincreasing,outputvoltageincreases

attherateofcurrentlimitchargingCOUT.

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