SC4525D View Datasheet(PDF) - Semtech Corporation
Part Name
Description
MFG CO.
'SC4525D' PDF : 21 Pages View PDF
AC
=
−
2
0
⋅
log
1
GCAR
S
⋅1
2πFCC O
⋅ VFB
VO
SC4525D
AppliAcCa=ti−o2n0s⋅
Ilongforma1tion
28 ⋅ 6.1 ⋅10
−(3C⋅o2nπt⋅.8)0
⋅
1
1
03
⋅ 22 ⋅10 −6
⋅ 1.0 = 15.9dB
3.3
(2) Select the open loop crossover frequency, FC, between
10%
and
20%
of
the
15.9
switching
frequency.
At
FC,
find
the
rceeqraumireiRcd7oc=uotm0p.pu21te8n0c⋅as12ap0t0aoc−ri3tgoa=risn2, ,2tAh. 3Ce.kIEnStRypziecraol
applications with
is neglected and
7
R7 =
10 20
0. 3 ⋅ 10−3
= 7. 4 k
t he reqACC uC58ir=e==d−22c π2πo0⋅⋅m16⋅p60loe0⋅gn 1⋅s01Ga031tC1o13A⋅rR2⋅ g22Sa.2⋅1in.21⋅πa1⋅tF0 11CF03CC3cO=a=0⋅n1V.V4bF2OB5epneFFstim(a9t)ed by
C5 =
1
2π ⋅ 7⋅10 3⋅ 7.4 ⋅ 10 3
= 3.1 nF
C8 =
1
2 π ⋅677⋅103 ⋅ 7.4 ⋅103
= 32 pF
(2(340))%UPsloaefAcVVtteCochh=e=ethcc−(e1roo2mc+s0ospsom⋅e1/lv5onp.Ge9ωgserPpanWf)tr2Ms(oe1a8(rq1t+op⋅u+6reso.nls/z11eRceω,⋅yrEF1no,SPQRF0,1,CCF−+.t3OZo1s),⋅2c2ba/nπeωtc⋅wn2e8)le0teh⋅n1e
110% and
03 ⋅22 ⋅1
ESR zero,
0
−6
⋅ 1.0 = 15.9dB
Se3le.3ctR7=7.32k, C5=3.3nF,
Compensator parameters
and C8= 33pF for the design.
for various typical applications
FZ.
R7
=
10 20
0.28 ⋅10
−3
= 22.3k
are listed in Table 4. A MathCAD program is also available
upon request for detailed calculation of the compensator
(c5a)nTbheeCGnc5Pa,Wl=tcMhu2e≈laπptG⋅ea1CdrA6Rab⋅mR⋅y1Se0t, e31r⋅s2o2f.1th⋅ eω1 0pco3≈m=Rp1C0eO. 4n,s5antFion
neωtwZ o=rkR
1 par,ameters.
ESRCO
Thermal Considerations
CR87
==
AC
10 20
2gπm⋅ 60
0
⋅
1
10 3
⋅ 22.1 ⋅10 3
= 12pF
For the power transistor inside the SC4525D, the
CVo5
Vc
C8
=1
= 2 πFZ1 RG7PWM (1 +
=(1 + s1 / ωp )(1 + s
2 πFP1 R 7
sRESR CO)
/ ωn Q + s 2
/
ωn2
)
(10)
conduction loss PC, the switching loss PSW, and bootstrap
circuit PloTsOsTAPLB=STP, cCan+ PbSeWes+tiPmBSaTte+dPaQs follows:
PC = D ⋅ VC E S AT⋅ IO
PQ = VIN ⋅ 2mA
whereGgPmW=M0≈.3mGCAAR/⋅VRiSs
,
the
EA
ωp
gain
≈
of
1,
tRhCeOSC4525D.
ωZ
=1,
R ESRCO
PS W
=
1
2
⋅
tS
⋅ VIN
⋅ IO
⋅ FS W
(11)
AC
E35xa0mkHpRzl,7e:1=2D1Veg0tmte2o0rm3i.n3eV/3thAe
voltage compensator for an
converter with 47uF ceramic
PB S
T
=
D
⋅
VB S
T
⋅
IO
40
oCuhtopoustCec5aa=plao2coiπptFo1Zrg1.aRin7 crossover frequency of 35kHz, and
wswhietcrehPiVnDBgST=tisi(m1the−eoDBf)St⋅ThVseDuN⋅pIPpONlytvroanltsaigsteoarn(sdeteS
is the equivalent
Table 3).
Table 3: Typical Switching Time
place
(20%
oCvfo8 lFt=aC)g2, eπaFnc1Pod1mRFp7P1e=ns6a7to7rkHzez.roFraonmd
pole at FZ1=7kHz
Equation (9), the
required compensator gain at FC is
PTIaNDbl=e(31..T1y~p1ic.a3l)s⋅wI2Oit⋅cRhDiCng time
Input Voltage
5V
Load Current
1A
2A
3A
6.86ns 9.71ns 12.5ns
AC =
−
20⋅
log
18.5
⋅
3.
1
53
⋅10−3
⋅
1
2π ⋅ 35⋅ 103 ⋅ 47⋅ 10−6
⋅
1.0
3.3
= 7 dB
12V
12.5ns 15.3ns 18ns
PTOTAL= PC + PS W + PBS T +InPaQddition, the quiescent current loss is
Then the compensator parameters are
PC = D ⋅ VC E S AT⋅ IO
PQ = VIN ⋅ 2mA
(12)
© 2011 Semtech Corp.
PS W
=
1
2
⋅
tS
⋅
VIN
⋅ IO
The
⋅ FS W
total
power
loss
of
the
SC4525D is therefore
www.semtech.com
14
IO
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