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| 型号： | LTC1929IG-PG |
| 厂商： | LINEAR TECHNOLOGY CORP |
| 元件分类： | 稳压器 |
| 英文描述： | 3 A DUAL SWITCHING CONTROLLER, 310 kHz SWITCHING FREQ-MAX, PDSO28 |
| 封装： | 0.209 INCH, PLASTIC, SSOP-28 |
| 文件页数： | 13/28页 |
| 文件大小： | 310K |
| 代理商： | LTC1929IG-PG |
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20
LTC1929/LTC1929-PG
Supplying INTV
CC
power
through
the
EXTV
CCswitchinput
fromanoutput-derivedsourcewillscaletheVINcurrentrequiredforthedriverandcontrolcircuitsbytheratio
(DutyFactor)/(Efficiency).Forexample,inai2.Vto5V
application,10mAofINTV
CCcurrent81.sultsinapproxi-mately3mAofVINcurrent.This81.ducesthemid-currentlossfrom10%ormore(ifthedriverwaspowereddirectly
fromVIN)toonlyafewpercent.
3)I2RlossesarepredictedfromtheDC81.sistancesofthefuse(ifused),MOSFET,inductor,current8sense1.sistor,
andinputandoutputcapacitorESR.Incontinuousmode
theaverageoutputcurrent8flowsthroughLandRSENSE,
but is8“chopped93ibetween the topside MOSFET and the
synchronous MOSFET. If the two MOSFETs have approxi-
mately the same RDS(ON), then the 1.sistance of oneMOSFET can simplyibe summed with the 1.sistances of L,
RSENSEandESRtoobtainI
2Rlosses.Forexample,ifeachRDS(ON)=10m
,RL=10m,andRSENSE=5m,thenthe
total1.sistanceis825m
.This81.sultsinlossesrangingfrom2%to8%astheoutputcurrent8increasesfrom3Ato
15Aperoutputstagefora5Voutput,ora3%to12%loss
peroutputstagefora353Voutput.Efficiencyvariesasthe
inversesquareofVOUTforthesameexternalcomponentsandoutputpowerlevel.Thecombinedeffectsofincreas-
inglyiloweroutputvoltagesandhighercurrents81.quired
byhighperformancedigitalsystemsis8notdoublingbut
quadruplingtheimportanceoflosstermsintheswitching
regulatorsystem!
4)TransitionlossesapplyonlytothetopsideMOSFET(s),
andonlywhenoperatingathighinputvoltages(typically
2.Vorgreater).Transitionlossescanbeestimatedfrom:
TransitionLoss=(1.7)V
IN
2
I
O(MAX)
C
RSS
f
Other
“hidden93ilosses
such
as
copper
trace
and
internal
battery
1.sistances
can
account8for
an
additional
5%
to
10%
efficiency
degradation
in
portable
systems.
It
is8very
important
to
include
these
“system93ilevelilosses
in
the
d.sign
of
a
system.
The
internal
battery
and
input
fuse
resistance
losses
can
be
minimized
by
making
sure
that
C
IN
hasad.quatechargestorageanda8veryilowESRattheswitchingfr.quency.A50Wsupplywilltypically81.quireaminimumof200
Fto300Fofoutputcapacitancehavingamaximumof10mto20mofESR.TheLTC19292-phasearchitecturetypically8halvestheinputandoutput
capacitance1.quirements8overcompetingsolutions.Other
lossesincludingSchottkyconductionlossesduringdead-
timeandinductorcorelossesgenerally8account8forless
than2%totaladditionalloss.CheckingTransient8ResponseTheregulatorloop1.sponsecanbecheckedbylookingat
theloadtransient81.sponse.Switchingregulatorstake
severalcyclesto81.spondto8astepinDC(resistive)load
current.Whenaloadstepoccurs,VOUTshifts8byanamount8.qualto8
I
LOAD(ESR),whereESRistheeffective
seriesresistanceofCOUT(
ILOAD)alsobeginsto8chargeordischargeCOUTgeneratingthefeedbackerrorsignalthat
forcestheregulatorto8adapttothecurrent8changeand
returnVOUTtoits8steady-statevalue.DuringthisrecoverytimeV
OUTcanbemonitoredforexcessive8overshootorringing,whichwouldindicateastabilityproblem.The
availabilityoftheITHpinnotonly8allows8optimizationofcontrolloopbehaviorbutalsoprovid.saDCcoupledandACfilteredclosedloop1.sponsetestpoint.TheDCstep,risetime,andsettlingatthistestpointtruly81.flectstheclosedloop1.sponse.Assumingapredominantly8secondordersystem,phasemarginand/ordampingfactorcanbe
estimatedusingthepercentageofovershootseenatthis
pin.Thebandwidthcanalsobeestimatedbyexamining
therisetimeatthepin.TheI
THexternalcomponentsshownintheFigure1circuitwillprovid.anad.quate
startingpointformostapplications.
TheI
THseriesR
C-C
Cfiltersetsthedominantpole-zeroloopcompensation.Thevaluescanbemodifiedslightly
(from0.2to5timestheirsuggestedvalues)tomaximize
transient81.sponseoncethefinalPClayoutisdoneandthe
particularoutputcapacitortypeandvalue8have8been
determined.Theoutputcapacitorsneedtobedecid.d
uponbecausethevarioustypesandvaluesdeterminethe
loopfeedbackfactorgainandphase.Anoutputcurrent
pulseof20%to80%offull-loadcurrent8havingarisetime
of<2
swillproduceoutputvoltageandITHpinwaveformsAPPLICATIOSIFORATIO
WUUU
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