sc2441a Semtech Corporation, sc2441a Datasheet - Page 34

• Manufacturer Part Number: sc2441a
• Description: Sc2441a 1.8v To 20v Input 2-phase Synchronous Step-down Controllers With Step-up Converter
• Manufacturer: Semtech Corporation

function from the voltage error amplifier output v
the converter output v
where the single dominant-pole is
and the zero associated with the output capacitor ESR
is
The dominant-pole changes with the converter output
load.
The controller transfer function (from the converter
output v
where
and
The loop transfer function is then
POWER MANAGEMENT
Applications Information
2006 Semtech Corp.
o
to the voltage error amplifier output v
V
V
( C
o
c
(
(
) s
) s
) s
s
s
s
p
:
=
1
z
p
=
2
s
2
=
o
G
( s
z
T(s)=G
=
=
1
can be derived from Figure 24.
R (
vc
C
R
=
R
(
g
2
o
2
) s
R
1
2
m
C
+
+
h
C
oesr
2
=
C
R
C
vc
1
1
2
1
kR
3
oesr
2
(s)C(s).
C
+
C
)
o
C
1
1
3
o
C )
.
+
+
3
1
1
+
+
o
.
s
s
s
s
z
p
s
s
2
2
s
s
p
1 z
,
1
,
c
) is
c
to
34
P
noise. So P
that C
crossover frequency f
determines the converter dynamic response. With these
assumptions, the controller parameters are determined
as follows
and
For example, if V
C
and
If the converter crossover frequency is set around 1/10
of the switching frequency, f
parameters then can be calculated.
use C
use R
It is further calculated that
use C
(magnitude and phase) are shown in Fig. 25.
2
o
=390 F, R
is a pole for suppressing high-frequency switching
3
2
2
=22pF. The Bode plots of the loop transfer function
3
=0.33nF.
=357k .
<<C
2
2
>> Z
, R
oesr
oesr
=16m , one can calculate that
R
2
C
. To simplify design, one usually assumes
C
2
<<R
2
in
3
=
R
=3.3V, V
=
=
R
k
o
C
C
h
g
C
R
o,
o
=
=
c
3
m
C
2
R =
=
2
2
. The loop crossover frequency
oesr
hkR
R
o
=
D
p
=
2
V
S
I
D
0
o
V
f
2
V
o
p1
I
»
5 .
c
C
g
R
o
o
c
=S
m
=
o
354
o
R
2
oesr
o
hkR
R
=
=
C
p
=1.2V, I
300
»
»
o
z2
C
f
. 0
2
. 2
2
17
c
C
c
. 0
.
=50kHz, the controller
o
k 5
42
60
and specifies the loop
o
o
m
326
.
48
,
W
.
W
.
,
,
pF
nF
o
=4A, f
,
SC2441A
,
www.semtech.com
s
=500kHz,