SC2453 Semtech Corporation, SC2453 Datasheet - Page 9

• Manufacturer Part Number: SC2453
• Description: High Performance Quad Output Switching Regulator
• Manufacturer: Semtech Corporation

PWM CONTROLLER
SC2453 is a voltage mode buck controller that utilizes
an externally compensated high bandwidth error ampli-
fier to regulate output voltage. The power stage of the
synchronous rectified buck converter control-to-output
transfer function is as shown below:
where,
L – Output inductance
C – Output capacitance
R
V
Figure 1. Voltage Mode Buck Converter Compensation
Network
POWER MANAGEMENT
Applications Information (Cont.)
G
IN
C
O
2002 Semtech Corp.
VD
– Output capacitor ESR
– Input voltage
(
) s
LC
1
C2
V
IN
R1
1
R3
1
s
R
L
sR
Vref
C
s
C
2
LC
-
+
R2
C3
C1
9
The transfer function of the compensation network is as
follows:
where,
The design guidelines are as following:
1. Set the loop gain crossover frequency
2. Place an integrator in the origin to increase DC and
3. Select
4. Cancel
5. Place a high frequency compensation pole
Figure 2. Asymptotic diagram of buck power stage and
its compensated loop gain.
G
Gd
0dB
I
Z
COMP
T
1
switching frequency.
low frequency gains.
to dampen peaking; the loop gain has –20dB rate
to go across the 0dB line for obtaining a wide band-
width.
half switching frequency to get the maximum attenu-
ation of the switching ripple and the high frequency
noise with the adequate phase lag at
R
R
(
1
) s
(
2
1
C
C
1
1
1
,
s
C
Z1
I
ESR
Z
3
2
and
1 (
1 (
)
,
with compensation pole
Z1
R (
P
1
s
s
1
P
Z
Z2
1
1
o
)(
)(
R
1
R
such that they are placed near
1
1
3
1
3
C
C )
2
Z2
s
s
,
2
P
Z
2
2
P
)
)
2
c
Loop gain T(s)
R
ESR
2
C
PRELIMINARY
C
1
1
p1
1
C
www.semtech.com
SC2453
C
P1
3
3
(
C
.
C
p2
P1
for given
P2
=
at the
ESR
).
O