SC4525CEVB View Datasheet(PDF) - Semtech Corporation

Part Name

Description

MFG CO.

SC4525CEVB

28V 3A Step-Down Switching Regulator

Semtech Corporation 

Applications Information (Cont.)

Closed-loop measurement shows that the SC4525C

minimum on time is about 120ns at room temperature

(Figure 4). If the required switch on time is shorter than

the minimum on time, the regulator will either skip cycles

or it will jitter.

To allow for transient headroom, the minimum operating

switch on time should be at least 20% to 30% higher than

the worst-case minimum on time.

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a1chV.0OiVts−s1et

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 O1V+.0FOSVVWD −)⋅⋅L1(11 − D )

(3)

winhdeurcetLDa1nF=Sc=WeV(.INVis2O+V0+tVOh%DVe+D⋅−I)VOsV⋅Dw(⋅C1FEiSt−WAcTDhi)ng frequency and L1 is the

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

maamnadxoianmsgIDsRuueMImLmfSf_=iicCnliIo(NegVanO=3dc5I+yOF%c, SVcu⋅WDoirnr)sD⋅edt⋅Ln(ua⋅11t(nc1, t−doI−ODsr,Di)rzig)epi.pvRelees-caaurrrargenongoti,ndtghceEoqimnudaputriocotmnori(s3ies)

given by

LD 1VO==(VDO3 IL5+%⋅ VED⋅ IS)O ⋅R⋅(1F+S−W8D ⋅)FS1W ⋅ C O 

(4)

If the input voltage varies over a wide range, then choose

Lco1 nbvaesrIeRteMdrS

CIN

The peak

on the nominal input voltage. Always verify

>_oCpINer=aItOiIoO⋅n aDt⋅t(h1e−inDp)ut voltage extremes.

cu4rr⋅eDnVtINlim⋅ FiStWof SC4525C power transistor is at

least

3.9A.

DVO

T=hDeILm⋅ axEiSmRu+m8d⋅eFlSiv1Wer⋅ aCbOle

load

current

for

the

1.0V 

R4

D

=

=

R

6





VO −

1VO.0+VVD

1





VIN + VD − VCESAT

SC4525C

D=

VO + VD

VIN + VD − VCESAT

DIL

SC4525C

=

is

(VO + VD ) ⋅ (1 − D)

3.9AFmSWin⋅uLs1 one

half

of

the

inductor

ripple

cInuprruetnDDLt.1IeL c==o(u(VVp2OOl0+in+%FVgSVD⋅WIDC)O⋅)a⋅(⋅⋅L1pF(11Sa−Wc−Dit)Do)r

TrihpeplienpLcIR1uuMrtS=r_ce(CanVIpNt2Oao=0+cf%IitVaOoD⋅b⋅rI)Ou⋅s(⋅Dch1FkoS⋅−Wuc(1oDldn−) vbDee)rtcehro. Tshenis

to handle the

value is given

RMS

by

AC =

AC =

R7 =

RC75 ==

CC58 ==

C8 =

Vo =

Vc

I RMS _ CIN = IO ⋅ D ⋅ (1 − D)

(5)

TinhpeuitnrpDipuVptOlce=avpDoaIlcLtai⋅tgaeEnScweRitm+hiun8sst⋅pFaSel1Wscoi⋅fibCceaOthioignh. Tehnisoiusgimh ptoorkteaenpt

iinnpruetdcuDacVpinOagc=ittDahIneLc⋅ecoEcnaSdnRub+ceti8eves⋅tFiESm1WMaI⋅tCefrdOomfrotmhe regulator. The

Vo =

Vc

GPWM

GPWM

RA7C

=

=

RC 4IN=>R64 ⋅1DV.V0OIIOVN ⋅ −F1SW

(6)

RC75 ==

AwC h=er−e2CDD0INV=⋅IN>lois4gt⋅hVGDeOCV1IaA+IONRllVo⋅SDFw⋅SaW2bπlFe1CiCnpO u⋅tVVrFiOBpple voltage.

AC =

CC58 ==

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

A(aCare=fewt−h2em0Wid⋅)leoaagnldc2ch8aon⋅ic6ee.a11sf⋅oil1yr0hin−a3pnu⋅d2tleπfhi⋅lti8ge0hrin⋅R1gM0. S13Ar⋅ips2ip2nlge⋅1lce0u4−rr6.e7⋅nµ13tF,..03 CR=871==5

RCCAAXsfvpsO758CCowaol5uart=====lRiitcttsapc20e22f−−cgyh0du.eππ222eLIiD0b1trRni⋅⋅8100akMnaIoC016gLmHpS=t⋅⋅⋅a60p1=_h1ll2pfz5ipoo00ra.Cc(9⋅0letIgg(Va1riNthc⋅Vqac2−Oco01ae3Ola=ui0G2l+t0t3ep1eEiI+%8o=51ColOF3aVn⋅S1A0rwnDc22SV⋅⋅RRc⋅⋅0WI6iDs)222yOitSka,t⋅.o)..2⋅Dh1a1(⋅Hna13⋅1⋅rLF.p(dszk⋅2⋅1aS11i⋅−m1(sWp1π1bl⋅s−D0lo0aaF1uiw1−cw)dCl−D0l3la3kiCDect)3tEc=qceOi⋅)oShar=u20naR⋅ipanπ1.mVsa4Vteg,2F⋅ecO5ilBa8pceintfnfc0Foa(rF1dtenr⋅rµqo1c51Fuel000yoe1r0µt3enrikFc⋅q2cH2cyu.i2sz2a.iµrpaoe⋅FFa1drmo)ce0rhcieqta−iongh6unrthiasg⋅btet.13hoeer..03

C5 =

C8 =





= 15

Vo =

Vc

RCVVTe oc75hx==p=er(0o2e1u.sπ2Ds+ t1⋅e8pV01sduO⋅6/11t2a5=G0.ω9⋅r0s1iPDpp −W0)3IpM(L131l(=e⋅1⋅+22vE+so22S sl/..tR1R3ωakEg+⋅nS1eQR80CD+ ⋅3OVFs)OS=21Wo0/f⋅.ωCa4 n25Ob)nuFck

converter

(7)

can

be

RGCVVwSdtA7Poc8hiWenh=2e==Mcce2rr1ee(re2≈µ1egf0aFoπCGm+tsCAr2⋅hteC0IeCO6NosesARit0/s>4⋅h(G0Rωi7tEen4hPSµqp⋅dWhe1)⋅F,uuM(iD01ogaXc(1Vtu1h3t+5IiIoOtoNeR⋅+psrsn2⋅utcs/F2reRtwSω(i.3rpWc1EhanSω)ap)mQRe⋅p,pl1Cnea+it≈0cOcVhsc)3icRIetN2uaa1C=irp/nsorO1aωecau,cen2tn2ti.pptti)toFusDrtmIiLsraifpxionipumcωlnreueZdmav=sao.edRlsteEaqS1gaRuCesaOtDies,

CCGfiiP58nnoWdr==Mtuoh22c≈uetππtoGpFAForCC11uPZuA11Rctt⋅uRRpfRiru77lrStete,nrcitnapgoaficnaitmobrωuopcisskt≈ancRpoo1CptnOlviac,earcttoieonrncdse.irrneRcωibtplZeyp=clefaeRuceEsudSe1rRsrCetChO1nOe1,t,

R = 10 20

GPWM

R7 =

C5 =

C8 =

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