SC4601EVB データシートの表示（PDF） - Semtech Corporation
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SC4601EVB Datasheet PDF : 18 Pages
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SC4601
POWER MANAGEMENT
Applications Information - (Cont.)
After the compensation, the converter will have the
following loop gain:
T(s) = GPWM ⋅ GCOMP (s) ⋅ GVD (s) =
1
VM
⋅ ωI ⋅ VI
s
1+ s
⋅
1+
ωZ1
s
ωP1
1+ s
⋅
⋅
1
+
ωZ2
s
ωP2
1+
s
1
⋅
1
+
s
RC ⋅ C4
L
R
+
s2LC
Where:
GPWM = PWM gain and
VM = 1.5V, ramp peak to valley voltage of SC4601.
The design guidelines for the SC4601 applications are
as following:
1. Set the loop gain crossover corner frequency
ωC for given switching corner frequency
ωS =2 πfs,
2. Place an integrator at the origin to increase DC
and low frequency gains.
3. Select ωZ1 and ωZ2 such that they are placed
near ωO to damp the peaking and the loop gain
has a -20dB/dec rate to go across the 0dB
line for obtaining a wide bandwidth.
4. Cancel the zero from C4’s ESR by a compensa-
tor pole ωP1 (ωP1 = ωESR = 1/( RCC4)),
5. Place a high frequency compensator pole ωp2
(ωp2 = πfs) to get the maximum attenuation of
the switching ripple and high frequency noise
with the adequate phase lag at ωC.
The compensated loop gain will be as given in Figure 4:
T
ωZ1
ωo
Loop gain T(s)
ωZ2
-20dB/dec
Gd
ωc
0dB
ωp1
ω p2
Synchronous & Multi-phase Operation
The SC4601 has a SYNC/SLEEP pin, which can be used
to synchronize the controller to a faster external clock.
The SC4601 can be also used in conjunction with
Semtech’s multi-phase link (SC4201), to synchronize and
multi-phase several controllers. Feeding outputs A/B/C/
D of SC4201 to the SYNC inputs of several SC46xx con-
trollers, it is easy to displace the controllers by 2, 3 or 4
phases. Additionally the SC4201 can be synchronized to
an external clock so that everything runs under one fre-
quency. This synchronizing operation avoids frequency
beating among different controllers, simplifies noise fil-
tering. This multi-phasing control displaces the control-
lers by 90o/120o/180o degrees, and simplifies tremen-
dously the input filtering requirements for the system.
Figure 5 shows one possible application.
Figure 5. Breakthrough, innovative solution to meet the
next generation of networking and industrial power re-
quirements.
Power stage GVD(s)
-40dB/dec
ω ESR
Figure 4. Asymptotic diagrams of power stage and its
loop gain.
2006 Semtech Corp.
12
www.semtech.com
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