SC2612C Semtech, SC2612C Datasheet - Page 7

• Manufacturer Part Number: SC2612C
• Description: 600kHz/200kHz Step-Down DC/DC Converter
• Manufacturer: Semtech

Having plotted the line ABCD, and confirmed the type of
compensation necessary, compensation component val-
ues can be determined.
At Fco, the line ABCD shows a gain of -27.5dB and a slope
of -20dB/decade. In order for the total open loop gain to
be 0dB with a -20dB/decade slope at this frequency, the
compensated error amp gain at Fco must be +27.5dB
with a 0dB slope. This is the line FG on the plot below.
Since open loop DC gain should be as high as possible to
minimize errors, a zero is placed at F and to minimize
high frequency gain and switching interference a pole is
placed at G.
The zero at F should be no higher than Fco/4 and the
pole at G no lower than 4*Fco. The equations to set the
gain and the pole and zero locations are:
For this example, this results in the following values.
Rs
Rs
Cs
Cp
Cs
Cp
POWER MANAGEMENT
2003 Semtech Corp.
100
=
-20
-40
-60
Fig2: Type 2 Error Amplifier Compensation
=
=
=
»
100.0E+0
»
80
60
40
20
0
10
2
10
2
6
6
gm
E
A
× p
0
× p
×
×
20
27
.
A
25
400
20
8
Fz
Fp
.
5
1
1
×
where
1
=
10
1
×
×
×
10
29
Rs
Rs
1
3
1
×
3
.
30
6
×
30
k
Fp(lc)
1.0E+3
A
W
×
10
×
=
10
»
3
gain
B
30
3
=
Fz(esr)
=
k
C
0
W
.
14
at
22
pF
Frequency (Hz)
Fco
nF
Filter+modulator
+divider gain
10.0E+3
(unecessar
(in
Compensated
Error Amp gain
dB)
F
Fz1
y
100.0E+3
Fco
due
to
Fp1
EA
Total open
loop gain
G
rolloff
1.0E+6
D
H
)
7
www.DataSheet4U.com
SC2612A/C
www.semtech.com