SC2446A Semtech Corporation, SC2446A Datasheet - Page 18

• Manufacturer Part Number: SC2446A
• Description: Dual-Phase Single or Two Output Synchronous Step-Down Controller
• Manufacturer: Semtech Corporation

R
output voltage is regulated with satisfactory dynamic
performance.
With the output voltage V
and the feedback resistor values are determined using
the equations given in the “Output Voltage Setting”
section with
For the rated output current I
k is first estimated as
From the transfer function from the voltage error
amplifier output v
where, the single dominant pole is
and the zero due to the output capacitor ESR is
The dominant pole moves as output load varies.
The controller transfer function (from the converter
output v
where
and
POWER MANAGEMENT
Application Information (Cont.)
o2
2005 Semtech Corp.
and the current sensing gain, such that the converter
o
to the voltage error amplifier output v
V
V
( C
o
c
(
(
c
) s
) s
) s
s
to the converter output v
p
s
:
1
p
s
2
s
G
( s
z
1
R (
z
h
vc
2
k
C
R
(
g
o
o
2
) s
R
2
m
known, the feedback gain h
0
R
2
h
C
V
oesr
I
R
5 .
C
o
C
1 .
2
o
o
1
1
2
1
1
C
, the current sensing gain
oesr
kR
3
2
C
.
.
)
C
2
o
C
1
1
,
3
o
C )
.
3
1
1
o
.
s
s
s
s
,
z
p
s
s
2
2
s
s
1 z
p
,
1
.
o
is
c
) is
18
The loop transfer function is then
To simplify design, we assume that C
selects S
frequency f
determines the converter dynamic bandwidth. With these
assumptions, the controller parameters are determined
as following.
and
with a constant K.
For example, if V
R
and
If the converter crossover frequency is set around 1/10
of the switching frequency, f
parameters then can be calculated as
where,
(260 µ
If we use C
oesr
=4.67m , one can calculate that
g
m is the error amplifier transconductance gain
1
).
p1
2
c
=S
. It is noted that the crossover frequency
= 0.33 nF,
z2
C
o
=2.5V, I
R
and specifies the loop crossover
2
2
R
C
o
k
C
g
h
R
3
R
T(s)=G
m
2
2
C
hkR
2
o
V
I
2
C
o
o
0
I
2
f
V
R
=15A, f
o
o
1 .
c
g
5 .
o
o
R
m
oesr
o
2
R
hkR
C
o
167
vc
2
C
. 7
848
C
c
2
f
(s)C(s).
0
c
. 0
= 30kHz, the controller
o
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o
14
, 2 .
o
m
,
328
, K
s
.
,
=300kHz, C
.
k 5
,
nF
,
SC2446A
.
3
<<C
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2
, R
o
=1.68mF,
oesr
<<R
o,