SC2620 Semtech Corporation, SC2620 Datasheet - Page 18

• Manufacturer Part Number: SC2620
• Description: 30V Step-down Regulator
• Manufacturer: Semtech Corporation

If C
situates well beyond half the switching frequency. The low
frequency gain of the control-to-output transfer function is
simply the product of power stage transconductance and
the equivalent load resistance (Figure 12).
The transfer functions of the feedback network and the
error amplifier are:
and
provided that
In Equation (10), C
output resistance R
high frequency pole p
POWER MANAGEMENT
Applications Information
2008 Semtech Corp.
1
R
v
v
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v
is ceramic, then its ESR zero can be neglected as it
v
OUT
COMP
O
p
FB
1
FB
Amplifier
Transcondu
R
R
1
1
O
1
R
C
C
G
2
5
sC
5
R
MA
2
Open
5
R
5
R
forms a low frequency pole p
O
O
C
O
1
of the error amplifier and C
3
1
6
with R
c
Loop
1
and
1
s
tan
sC
R
sC
1
5
sC
ce
R
Gain
R
5
:
11
5
R
O
6
Figure 11. Simplified Control Loop Equivalent Circuit
C6
R
R
2
V
V
IN
5
1
C
COMP
11
R5
R
C5
280
5
53
.
dB
RO
1.6M
1
GMA =
280
GMP = 8
1
1
POWER
6
STAGE
with the
6 .
forms a
-1
REFERENCE
-
+
VOLTAGE
M
(10)
-1
(9)
FB
1V
18
In addition C
The
band gain (between z
overall loop gain T(s) is the product of the control-to-output
and the output-to-control transfer functions. To simplify
resistive. If the overall loop gain is to cross 0dB at one
tenth of the switching frequency (
decade, then its mid-band gain (between z
be
v
T
v
COMP
j (
OUT
C11
Z
)
p
1
p
C
3
2
Bode plot, the feedback network is assumed to be
R1
R2
v
output-to-control
v
COMP
C
R
FB
R
1
5
10
5
1
ESR
5
R
I OUT
1
C
n
C1
C
and R
S
OUT
5
6
v
v
OUT
FB
R OUT
5
is also shown in Figure 12. Its mid-
form a zero with angular frequency:
V OUT
S
1
C
10
and p
1
R
n
OUT
3
) is
transfer
C
G
MA
10
R
S
5
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SC2620
R
5
1
1
f
R
and p
) at –20dB/
2
R
function
2
2
. The
) will