sc2608 Semtech Corporation, sc2608 Datasheet - Page 8

• Manufacturer Part Number: sc2608
• Description: Sc2608 Simple, Synchronous Voltage Mode Pwm Controller
• Manufacturer: Semtech Corporation

POWER MANAGEMENT
(5) The compensation capacitor is determined by choosing
the compensator zero to be about one fifth of the output
filter corner frequency:
SC2608 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 provided
here with Mathcad. The phase margin can then be
checked using the Bode plot.
Applications Information (Cont.)
©
2005 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 procedure
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
4
in
i
c
=15A
=1nF
4
=1.33KΩ
=2.5V
=12V
=200KHz
1 . 10
1 . 10
5
5
set to
set to
V
G
V
C
R
R
C=100nF
1 . 10
1 . 10
ramp
bg
m
o
c
c
=4400uF
=0.009 Ω
=1.5KΩ
=0.007A/V
=0.8V
6
=1V
6
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SC2608