TS51221 datasheet(7/18 Pages) SEMTECH

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TS51221

Final Datasheet

Rev 1.1

April 6, 2015

www.semtech.com

7 of 18

Semtech

Functional Description

TheTS51221wirelesspowerreceiverdeviceisaswitching

converterthatincludesflexibilitytobeusedforawiderange

ofinputvoltagesandisoptimizedforhighefficiencypower

conversionwithlowR

DSONintegratedsynchronousswitches.A

1MHzinternalswitchingfrequencyfacilitateslowcostLCfilter

combinations.Additionally,thefixedoutputversionsenable

aminimumexternalcomponentcounttoprovideacomplete

regulationsolutionwithonly4externalcomponents:aninput

bypasscapacitor,aninductor,anoutputcapacitor,andthe

bootstrapcapacitor.

Detailed Pin Descripttion

Unregulated input, VCC

Thisterminalistheunregulatedinputvoltagesourcefrom

therectifiedreceivercoilvoltage.Itisrecommendedthata

10uFbypasscapacitorbeplacedclosetothedeviceforbest

performance.SincethisisalsothemainsupplyfortheIC,

goodlayoutpracticesneedtobefollowedforthisconnection.

Bootstrap control, BST

Thisterminalwillprovidethebootstrapvoltagerequiredfor

theupperinternalNMOSswitchofthebuckregulator.An

externalceramiccapacitorplacedbetweentheBSTinput

terminalandtheVSWpinwillprovidethenecessaryvoltage

fortheupperswitch.Innormaloperationthecapacitoris

re-chargedoneverylowsidesynchronousswitchingaction.

Inthecaseofwheretheswitchmodeapproaches100%duty

cycleforthehighsideFET,thedevicewillautomaticallyreduce

thedutycycleswitchtoaminimumofftimeonevery8thcycle

toallowthiscapacitortore-charge.

Sense feedback, FB

Thisistheinputterminalfortheoutputvoltagefeedback.

Forthefixedmodeversions,thisshouldbehookeddirectly

toV

OUT.TheconnectiononthePCBshouldbekeptasshort

aspossible,andshouldbemadeascloseaspossibletothe

capacitor.Thetraceshouldnotbesharedwithanyother

connection.(Figure23)

Foradjustablemodeversions,thisshouldbeconnectedto

theexternalresistordivider.Tochoosetheresistors,usethe

followingequation:

VOUT=0.9(1+RTOP/RBOT)

TheinputtotheFBpinishighimpedance,andinputcurrent

shouldbelessthan100nA.Asaresult,goodlayoutpractices

arerequiredforthefeedbackresistorsandfeedbacktraces.

Whenusingtheadjustableversion,thefeedbacktraceshould

bekeptasshortaspossibleandminimumwidthtoreduce

straycapacitanceandtoreducetheinjectionofnoise.

Fortheadjustableversion,theratioofVCC/VOUTcannotexceed

16.

Switching output, VSW

Thisistheswitchingnodeoftheregulator.Itshouldbe

connecteddirectlytothe4.7uHinductorwithawide,short

traceandtooneendoftheBootstrapcapacitor.Itisswitching

betweenVCCandPGNDattheswitchingfrequency.

Ground, GND

Thisgroundisusedforthemajorityofthedeviceincludingthe

analogreference,controlloop,andothercircuits.

Power Ground, PGND

Thisisaseparategroundconnectionusedforthelowside

synchronousswitchtoisolateswitchingnoisefromtherestof

thedevice.(Figure23)

Enable, high-voltage, EN

Thisistheinputterminaltoactivatetheregulator.Theinput

thresholdisTTL/CMOScompatible.Italsohasaninternalpull-

uptoensureastablestateifthepinisdisconnected.

Power Good Output, PG

Thisisanopendrain,activelowoutput.Theswitchedmode

outputvoltageismonitoredandthePGlinewillremainlow

untiltheoutputvoltagereachestheVOUT-UVthreshold.Once

theinternalcomparatordetectstheoutputvoltageisabove

thedesiredthreshold,aninternaldelaytimerisactivatedand

thePGlineisde-assertedtohighoncethisdelaytimerexpires.

IntheeventtheoutputvoltagedecreasesbelowVOUT-UV,the

PGlinewillbeassertedlowandremainlowuntiltheoutput

risesaboveVOUT-UVandthedelaytimertimesout.SeeFigure2

forthecircuitschematicforthePGsignal.

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