L =
OD
20%⋅IO ⋅FSW
IRMS _ CIN = IO ⋅ D ⋅ ( − D)
SC4524B
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=oRr6eachV.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=(vV6DoO3 IlL5t+aV.%⋅0gOVVeED⋅ IS)Ov −⋅Ra⋅(rF+ieS−Ws8Do ⋅)vFeSWr a⋅ wC Oide range,
(4)
then choose
Lco1 nbvaesrIeRteMdrS
CDIN=
The peak
on the nominal input voltage. Always verify
>_coVCuIpNI4Nrer+⋅er=VaDnVOItVODtiI+oIONl⋅−inVm⋅VDFaDCitStEW⋅Sto(AhTfeS−iCnD4p)5u2t4vBolptaogweeerxttrraenmsiesst.or is at
lSceuCar4sr5te2n2D4Dt.6.BVIALO.i=sT=h(2DVe.6OILmA+⋅FamSVxEWDiSimn)⋅R⋅uLu(+smo8−dnD⋅eeF)lSivhWear⋅lafCboOlfe
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⋅tgaeEnScweRitm+hiun8sst⋅pFaSelWscoi⋅fibCceaOthioignh. 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=⋅INloisgthVGeOCaA+RllVoSDw⋅ a2bπlFeCiCnpO u⋅tVVrFiOBpple voltage.
AC =
C8 =
Multi-layerVcINe+raVmDic− cVaCEpSaATcitors, which have very low ESR
A(aCare=fewt−h2em0Wid⋅)leoaagnldc2ch8aon⋅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−Oco0ae3Ola=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⋅ecO5ilBa8pceintfnfc0Foa(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)nuFck
converter
(7)
can
be
GPWM
RGCAAVVwSdtA7Poc8CChiWenh=1e===Mcce0rree(re2−−≈µegf0aFoπ22CGm+tsCAr2⋅ht00eC0IeCO6NosesAR⋅⋅it0/s>4ll⋅hoo(G0Rωi7tEengg4hPSµqp⋅dWhe)⋅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)to0FusDrtm⋅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+sSFhcPsidgh/ihoRoGω-t7dsPtpWike)dM(ye(rbe+cavu+srerrsr/rieseRωernEnStdQRriseCo+ecdOnos)esv2sien/argyωs n2ifnir)neptehuwethSecCeu4lrir5ne2gn4trBe.csTptihifkieeesrses,
DV = DI ⋅ ESR +
GPWM
≈
R
GCA ⋅ R S
,
ωp
≈
RCO
,
ωZ
=
11,
R ESRCO