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PDF SC4525A Data sheet ( Hoja de datos )
| Número de pieza | SC4525A | |
| Descripción | 28V 3A Step-Down Switching Regulator | |
| Fabricantes | Semtech Corporation | |
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SC4525A
28V 3A Step-Down Switching Regulator
POWER MANAGEMENT
Features
Wide input range: 8V to 28V
3A Output Current
200kHz to 2MHz Programmable Frequency
Precision 1V Feedback Voltage
Peak Current-Mode Control
Cycle-by-Cycle Current Limiting
Hiccup Overload Protection with Frequency Foldback
www.DataSheeSt4oUft.c-Somtart and Enable
Thermal Shutdown
Thermally Enhanced 8-pin SOIC Package
Fully RoHS and WEEE compliant
Applications
XDSL and Cable Modems
Set Top Boxes
Point of Load Applications
CPE Equipment
DSP Power Supplies
LCD and Plasma TVs
Description
The SC4525A is a constant frequency peak current-mode
step-down switching regulator capable of producing 3A
output current from an input ranging from 8V to 28V. The
switching frequency of the SC4525A is programmable
up to 2MHz, allowing the use of small inductors and
ceramic capacitors for miniaturization, and high input/
output conversion ratio. The SC4525A is suitable for
next generation XDSL modems, high-definition TVs and
various point of load applications.
Peak current-mode PWM control employed in the
SC4525A achieves fast transient response with simple loop
compensation. Cycle-by-cycle current limiting and hiccup
overload protection reduces power dissipation during
output overload. Soft-start function reduces input start-
up current and prevents the output from overshooting
during power-up.
The SC4525A is available in SOIC-8 EDP package.
Typical Application Circuit
SC4525A
VIN 10V – 28V
C4
4.7mF
IN
BST
SW
SS/EN SC4525A
COMP
ROSC
FB
GND
C7
10nF
C8
10pF
R7
24.3k
C5
1nF
R5
18.2k
D1
1N4148
C1
0.1mF
L1
5.2mH
R4
33.2k
OUT
5V/3A
D2
20BQ030
R6
8.25k
C2
10mFX3
L1: Coiltronics CD1-5R2
C2: Murata GRM31CR60J106K
C4: Murata GRM32ER71H475K
Efficiency
90
80
VIN = 12V
VIN = 24V
70
60
50
40
0.0
0.5 1.0 1.5 2.0 2.5
Load Current (A)
3.0
Figure 1. 1MHz 10V -28V to 5V/3A Step-down Converter
November 8, 2007
Efficiency of the 1MHz 10V-28V to 5V/3A Step-Down Conve
1 page  
SC4525A
Pin Descriptions
SO-8 Pin Name Pin Function
1
SW
Emitter of the internal NPN power transistor. Connect this pin to the inductor, the freewheeling diode and the
bootstrap capacitor.
2 IN
3
4
www.DataSheet4U.com
ROSC
GND
5 SS/EN
6 COMP
Power supply to the regulator. It is also the collector of the internal NPN power transistor. It must be closely by-
passed to the ground plane.
An external resistor from this pin to ground sets the oscillator frequency.
Ground pin
Soft-start and regulator enable pin. A capacitor from this pin to ground provides soft-start and overload hiccup
functions. Hiccup can be disabled by overcoming the internal soft-start discharging current with an external pull-
up resistor connected between the SS/EN and the IN pins. Pulling the SS/EN pin below 0.2V completely shuts off
the regulator to low current state.
The output of the internal error amplifier. The voltage at this pin controls the peak switch current. A RC compensa-
tion network at this pin stabilizes the regulator.
7
FB
The inverting input of the error amplifier. If VFB falls below 0.8V, then the switching frequency will be reduced to
improve short-circuit robustness (see Applications Information for details).
8
BST
Supply pin to the power transistor driver. Tie to an external diode-capacitor bootstrap circuit to generate drive
voltage higher than VIN in order to fully enhance the internal NPN power transistor.
9
Exposed Pad
The exposed pad serves as a thermal contact to the circuit board. It is to be soldered to the ground plane of the
PC board.
5 Page 
L1 =
OD
20% ⋅IO ⋅FSW
IRMS _ CIN = IO ⋅ D ⋅ (1 − D)
SC4525A
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
www.DatatbmShheoeedeaatbe4tRtU.lea4.cinot=omaRbr6leeam1chV.a0OxiVtism−su1emt ,vtahlueen
the output voltage will not
in continuous-conduction
ITnhdeuicntDdou=rcStVoeINrle+rcVipVtOiDpo+l−neVVDcCuErSrAeT nt 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
maagmnivadexonianmsgbIDsRuuyeMImLmfSf_=iicCnliIo(NegVanO=3dc5I+yOF%c, SVcu⋅WDoirnr)sD⋅edt⋅Ln(ua⋅11t(nc1, t−doI−ODsr,Di)rzig)epi.pvRelees-caaurrrargenongoti,ndtghceEoqimnudaputriocotmnori(s3ies)
If theRiLDn 41Vp=O=uRt=(vV6DoO3 Il1L5t+aV.%⋅0gOVVeED⋅ IS)Ov −⋅Ra⋅1(r1F+ieS−Ws8Do ⋅)vFeS1Wr a⋅ wC Oide range,
(4)
then choose
Lco1 nbvaesrIeRteMdrS
CDIN=
The peak
>_cooVCunIpNI4Nrer+⋅ter=VhaDnVOIteVODtiI+oIONl⋅−ninmV⋅oVDFaDmiCtStEW⋅Stio(nAh1fTaeSl−iCniDn4p)p5u2ut5tvAovloptalotgawegeeer.xttArraelwnmsaieyssts.orveisriafyt
lSceuCar4sr5te2n3D5Dt.6.AVIALO.i=sT=h(3DVe.O6ILmA+⋅FamSVxEWDiSimn)⋅R⋅Luu(+11smo8−dnD⋅eeF)lSiv1hWear⋅laCf bOolef
load current
the inductor
for the
ripple
Input Decoupling Capacitor
TrihpeplienpLCc1uuINrt=r>ce(an4Vpt2Oa⋅o0+Dcf%iVtVaIoIODN⋅brI)O⋅u⋅sF(⋅ch1FSkoWS−WucoDldn) vbeertcehro. Tshenis
to handle the
value is given
RMS
by
I RMS _ CIN = IO ⋅ D ⋅ (1 − D)
(5)
TinhpeuitnrpDipuVptOlce=avpDoaIlcLtai⋅tgaeEnScweRitm+hiun8sst⋅pFaSel1Wscoi⋅fibCceaOthioignh. Tehnisoiusgimh ptoorkteaenpt
GPWM
in reducing the conductive EMI from the regulator. The
input capacitance can be estimated from
RA7C
=
=
RC 4IN=>R64 ⋅1DV.V0OIIOVN ⋅ −F1SW
(6)
AAwM(aCCarheu==feeltwtr−−ihe-l22emDaD00yVW=ied⋅⋅INr)llVeooaicIasNggnelt+rdhacVG2eVchmO8CDao1aA+in⋅Rci−lc6lVoeSecV.Dwa11aC⋅sEfpa2⋅oiSl1abAyrπTc0lFehi1itnC−aoi3CnpnrpusO⋅d,u2tl⋅ewtπfVVhirhF⋅liOtiBip8gecp0hhrilne⋅Rh1gMva0.ovS13Aeltra⋅ivps2geip2enrly.ge⋅ 1llceo0uw4−rr6.e7E⋅nµS13RtF,..03
C5 =
AC =
C8 =
R=71=5
RCCAAXsfvpsO758CCowaol5uart=====lRiitcttsapc20e22f−−cgyh0du.eππ222eLIiD0b1trRni⋅⋅8100akMnaIoC016gLmHpS=t⋅⋅⋅a60p1=_h1ll2pfz5ipoo00ra.Cc(9⋅0letIgg(Va1riNthc⋅Vqac2−Oco01ae3Ola=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⋅ecO5ilBa8pceintfnfc0Foa(rF1dtenr⋅rµqo1c51Fuel000yoe1r0µt3enrikFc⋅q2cH2cyu.i2sz2a.iµrpaoe⋅FFa1drmo)ce0rhcieqta−iongh6unrthiasg⋅btet.13hoeer..03
C5 =
C8 =
VV=oc 1=5
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)nuFck
converter
(7)
can
be
GPWM
RGRCCGCRCCCAAVVwSdtAfiiratvF7P7Poc758nn585o8CCehhonirWWenhdsr=2eee=========l=dMcMuttceu2rseorha11ee(l0er222e222−−≈Yµc≈w1tugeegfg00ai.t5πFtoππππntπ222eChoGGm+mtysC1pVAFAr2FF2o⋅⋅gh⋅t800erpeC0CI0ceCOC111u60N1o6PZsZuesAAoece111RR⋅⋅c⋅itt060it/1s>e4le1lls⋅⋅2hnu5RRpRooi(G00fR0R.ωir7ft9⋅nE0oiernuagg4f777h1lPrSµSiqp⋅vt⋅gfdm−Wetchee101)⋅Fe,cu,3iunM(G2iDrDe0a01ircog3a1iXcct(8y=1nn1CapVitu1h33t⋅1+5IAoipgtIocaoO⋅to22NeRRls⋅⋅+dapac6sofrsn.2222i⋅Spiceutwnc.s/tFa2..211iraoe1R3tw⋅tSω(i..mco3rprWck2⋅b1E1rh⋅asni1Sωr)ωapit1uπo)mQpRe⋅⋅hop0,plpFc101isCnep1arsa+ikCt−t≈0s≈0c3vlOcV3hCeansec)3i3cfcRIRe=tNOop2⋅uooaahc11CC==2irprt0p/nns⋅uiorOOgπl1o1a.vωecVriauaV4ch,r,eceun22F⋅tn2tOea5Bi.r8ptptpctti)nttptneoo0FuiFestomFuDrn.rtm⋅ntIic1pALsdsrefa0ie.viifprxril1oronnt3eipaReumiccωωt⋅dlirnbretup2iueZlZnderyp2umaegv==clsase⋅foaa.eied1bRRnulnscete0eEgEsadudqSSce11−gaRrRsahu6ZrCesCuetia5Cg⋅hOOsntDUiO1h3eees,,t,..03
R7 =
C5 =
= 15
C 8 =
CVVUreoc8easd=s=eiun(2oc1gefπ+sShF1cPsidg1h/ihoRoGω-t7dsPtpWike)dM(y1e(rb1e+cavu+srerrsr/rieseRωernEnStdQRriseCoe+cdOnos)esv2sien/argyωs in2fnir)netpehuwethSecCeu4lri5rne2gn5trAe.csTptihifkieeesrses,
DV = DI ⋅ ESR + 1
GPWM
≈
R
GCA ⋅ RS
,
ωp
≈
1
RCO
,
ωZ
=
R
1
ESRC
11,
O
11 Page | ||
| Páginas | Total 19 Páginas | |
| PDF Descargar | [ Datasheet SC4525A.PDF ] | |
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