SC4524A Ver la hoja de datos (PDF) - Semtech Corporation

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componentes Descripción

Fabricante

SC4524A

28V 2A Step-Down Switching Regulator

Semtech Corporation 

L =

OD

20%⋅IO ⋅FSW

IRMS _ CIN = IO ⋅ D ⋅ ( − D)

SC4524A

Vo =

Vc

Applications Information (Cont.)

Minimum Off Time Limitation

The PWM latch in Figure 2 is reset every cycle by the

clock. The clock also turns off the power transistor to

refresh the bootstrap capacitor. This minimum off time

limits the attainable duty cycle of the regulator at a given

switching frequency. The measured minimum off time is

100ns typically. If the required duty cycle is higher than

the attainable maximum, then the output voltage will not

be abRle4

mode.

t=oRr6eachV.0OiVts−set

value

in

continuous-conduction

InductDo=r SelecVtOio+nVD

VIN + VD − VCESAT

The inductor ripple current for a non-synchronous step-

down converter in continuous-conduction mode is

RD 4IL==R(6V OV+.0FOSVVWD −)⋅⋅L( − D )

(3)

winhdeurcetLDanF=Sc=WeV(.INVis2O+V0+tVOh%DVe+D⋅−I)VOsV⋅Dw(⋅CFEiSt−WAcTDhi)ng frequency and L1 is the

An inductor ripple current between 20% to 50% of the

maximum load current gives a good compromise among

easffsiucimenIDiRncMIgLyS,_=3cCI5o(NV%sO=t

I+aOnV⋅dD )Ds⋅iz(⋅e(.−R−DeD)-a) rranging Equation (3) and

iFnSdWu⋅cLto r ripple current, the inductor is

given by

If theRiLDn 4Vp=O=uRt=(vV6DoO3 IlL5t+aV.%⋅0gOVVeED⋅ IS)Ov −⋅Ra⋅(rF+ieS−Ws8Do ⋅)vFeSWr a⋅ wC Oide range,

(4)

then choose

Lco1 nbvaesrIeRteMdrS

CDIN=

The peak

on the nominal input voltage. Always verify

>_coVCuIpNI4Nrer+⋅er=VaDnVOItVODtiI+oIONl⋅−inmV⋅VDFaDiCtStEW⋅Sto(AhfTeS−iCnD4p)5u2t4vAolptaogweeerxttrraenmsiesst.or is at

lSceuCar4sr5te2n2D4Dt.6.AVIALO.i=sT=h(2DVe.O6ILmA+⋅FamSVxEWDiSimn)⋅R⋅Luu(+smo8−dnD⋅eeF)lSivhWear⋅laCf bOolef

load current

the inductor

for the

ripple

Input Decoupling Capacitor

TrihpeplienpLCcuuINrt=r>ce(an4Vpt2Oa⋅o0+Dcf%iVtVaIoIODN⋅brI)O⋅u⋅sF(⋅chFSkoWS−WucoDldn) vbeertcehro. Tshenis

to handle the

value is given

RMS

by

I RMS _ CIN = IO ⋅ D ⋅ ( − D)

(5)

TinhpeuitnrpDipuVptOlce=avpDoaIlcLtai⋅tgaeEnScweRitm+hiun8sst⋅pFaSelWscoi⋅fibCceaOthioignh. Tehnisoiusgimh ptoorkteaenpt

GPWM

in reducing the conductive EMI from the regulator. The

input capacitance can be estimated from

RA7C

=

=

RC 4IN=>R64 ⋅DV.V0OIIOVN ⋅ −FSW

(6)

C5 =

AwC h=er−e2DD0V=⋅INloisgthVGeOCaA+RllVoSDw⋅ a2bπlFeCiCnpO u⋅tVVrFiOBpple voltage.

AC =

C8 =

Multi-layerVcINe+raVmDic− cVaCEpSaATcitors, which have very low ESR

A(aCare=fewt−h2em0Wid⋅)leoaagnldc2ch8aon⋅ic6ee.asf⋅oilyr0hin−a3pnu⋅d2tleπfhi⋅lti8ge0hrin⋅RgM0. S3Ar⋅ips2ip2nlge⋅lce0u4−rr6.e7⋅nµ3tF,..03 R=7=5

RCCAAXsfvpsO758CCowaol5uart=====lRiitcttsapc20e22f−−cgyh0du.eππ222eLIiD0btrRni⋅⋅800akMnaIoC06gLmHpS=t⋅⋅⋅a60p=_hll2pfz5ipoo00ra.Cc(9⋅0letIgg(VariNthc⋅Vqac2−Oco0ae3Ola=ui0G2l+t0t3epeEiI+%8o=5ColOF3aVn⋅SA0rwnDc22SV⋅⋅RRc⋅⋅0WI6iDs)222yOitSka,t⋅.o)..2⋅Dha(⋅Hna3⋅⋅rLF.p(dszk⋅2⋅aSi⋅−m(sWpπbl⋅s−D0lo0aaFuiw−cw)dCl−D0l3la3kiCDect)3tEc=qceOi⋅)oShar=u20naR⋅ipanπ.mVsa4Vteg,2F⋅ecO5ilBa8pceintfnfc0Foa(rF1dtenr⋅rµqoc51Fuel000yoer0µt3enrikFc⋅q2cH2cyu.i2sz2a.iµrpaoe⋅FFadrmo)ce0rhcieqta−iongh6unrthiasg⋅btet.3hoeer..03

C5 =

C8 =



= 5

Vo =

Vc

RCVVTe oc75hx==p=er(0o2eu.sπ2Ds+ t⋅e8pV0sduO⋅6/t2a5=G0.ω9⋅r0siPDpp −W0)3IpM(L3l(=e⋅⋅+22vE+so22S sl/..tRR3ωakEg+⋅nSeQR80CD+ ⋅3OVFs)OS=2Wo0/f⋅.ωCa4 n25Ob)nuFck

converter

(7)

can

be

GPWM

RGCAAVVwSdtA7Poc8CChiWenh=1e===Mcce0rree(re2−−≈µegf0aFoπ22CGm+tsCAr2⋅ht00eC0IeCO6NosesAR⋅⋅it0/s>4ll⋅hoo(G0Rωi7tEengg4hPSµqp⋅dWhe)⋅F,uuM(G2iD0ogaXc(8CVtuh3t+5IAiIoO⋅toNeRR⋅+p6srsn2⋅Sutc.s/F2reRtw⋅Sω(i.3rpWc2⋅EhanSω)apπ)mQRe⋅p0,plFCnea+iC−t≈0cOcV3hCsc)3icRIetNO2⋅uaaC=2irp/ns⋅orOπaωecVauV,cen2F⋅tn2tOBi.8pptti)to0FusDrtm⋅IiLsra0ifpxion3ipumcω⋅lnre2ueZd2mav=sa⋅o.edRlste0EaqS−gaRu6Cesa⋅OtDi3es, ..03

R7 =

C5 =

 = 5

C 8 =

RCCGRCCfiiratv7P758nn5o8ehonWdsre=====l=dMuttusohal0e2222Yc≈tugeg0i.t5πtππntπ2eoGmypVFAF2o⋅g⋅8rpC0cCu06PZuAoceRc⋅t60itees⋅2nu5RRp0f0R.rf9⋅0oiruaf77lrSivt⋅fm−etce0ec,3inrea0irc3icty=nnap3⋅pgtoca22ls⋅aacof.222ipicwnta..2iao3t.mcorkbr⋅sirωituop⋅hopc0isparskts≈03vleane3cfR=opoohcC=rpt0nuiOglo.vria4chr,eu2ea5rtpctnttpneoiFetomFun.rntcpAdsefe.viirrlronteaReicωtdirbtupilZnerypueg=clsefaaiebRnunceegEsdudScerRsahZrCueti5CghOsnUOhee,t,

CF5re=e2wπhFeZe lRin7g Diode

CVVUreoc8easd=s=eiun(2ocgefπ+sShFcPsidgh/ihoRoGω-t7dsPtpWike)dM(ye(rbe+cavu+srerrsr/rieseRωernEnStdQRriseCoe+cdOnos)esv2sien/argyωs in2fnir)netpehuwethSecCeu4lri5rne2gn4trAe.csTptihifkieeesrses,

DV = DI ⋅ ESR +  

GPWM

≈

R

GCA ⋅ R S

,

ωp

≈



RCO

,

ωZ

=

 11,

R ESRCO

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