SC2446 Semtech Corporation, SC2446 Datasheet - Page 23

• Manufacturer Part Number: SC2446
• Description: Dual-Phase Single or Two Output Synchronous Step-Down Controller
• Manufacturer: Semtech Corporation

The transconductance error amplifier (in the SC2446)
has a gain g
design is to select the compensation network consisting
of C
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 Figure 17, 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
POWER MANAGEMENT
Application Information (Cont.)
o2
2004 Semtech Corp.
and the current sensing gain, such that the converter
2
, C
3
o
and R
to the voltage error amplifier output v
m
of 260
V
V
2
( C
, along with the feedback resistors R
o
c
(
(
) s
) s
) s
s
µ
p
:
1
A/V. The target of the compensation
s
G
( s
z
1
c
R (
h
vc
k
C
to the converter output v
(
g
o
o
2
) s
R
m
known, the feedback gain h
0
2
h
V
oesr
I
R
5 .
C
o
1 .
o
o
1
1
, the current sensing gain
oesr
kR
3
C
.
.
)
o
1
1
o
C )
.
1
1
o
s
s
s
s
,
z
p
s
s
2
2
s
s
1 z
p
,
1
.
c
) is
o
is
o1
,
23
and
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
oesr
=4.67m , one can calculate that
p1
c
=S
. It is noted that the crossover frequency
z2
o
=2.5V, I
and specifies the loop crossover
R
s
p
C
o
k
C
2
h
s
R
3
T(s)=G
2
z
2
2
V
I
R
2
o
o
0
I
V
=15A, f
o
R
o
1 .
g
5 .
2
o
R
m
oesr
R
C
R
2
hkR
C
C
o
167
2
vc
2
1
1
2
C
. 7
C
C
2
f
2
(s)C(s).
0
c
C
o
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2
o
14
, 2 .
C
o
m
,
,
3
, K
s
,
=300kHz, C
3
.
.
,
3
<<C
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SC2446
2
, R
o
=1.68mF,
oesr
<<R
o,