SC2608B Semtech Corporation, SC2608B Datasheet - Page 8

• Manufacturer Part Number: SC2608B
• Description: Synchronous Voltage Mode PWM Controller
• Manufacturer: Semtech Corporation

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POWER MANAGEMENT
(5) The compensation capacitor is determined by choos-
ing the compensator zero to be about one fifth of the
output filter corner frequency:
SC2608B soft start time is determined by the
compensation capacitor. Capacitance can be adjusted
to satisfy the soft start requirement.
(6) The final step is to generate the Bode plot by using
the simulation model in Fig. 4 or using the equations pro-
vided here with Mathcad. The phase margin can then be
checked using the Bode plot.
Applications Information (Cont.)
©
2007 Semtech Corp.
phase i ( )
C
mag i ( )
F
zero
=
2
π
135
180
100
=
R
45
90
50
50
0
0
1
•
10
F
10
F
5
o
zero
100
100
Fig. 5. Bode plot of the loop
Loop Gain Phase (Degree)
1 . 10
1 . 10
Loop Gain Mag (dB)
3
3
8
An example is given below to demonstrate the proce-
dure introduced above.
for suitable soft start time
F
F
i
set
i
1 . 10
1 . 10
F
R
V
V
L=2.2uH
C
C=327.95nF
I
o
sw
o
c
4
in
i
=15A
4
=1nF
=1.33KΩ
=2.5V
=12V
=250KHz
1 . 10
1 . 10
5
5
set to
set to
V
G
V
C
R
R
1 . 10
C=100nF
1 . 10
ramp
bg
m
o
c
c
=4400uF
=0.009 Ω
=1.5KΩ
=0.007A/V
=0.8V
6
=1V
6
SC2608B
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