8

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POWER MANAGEMENT

SC2608B

(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.)

(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.

An example is given below to demonstrate the proce-

dure introduced above.

set to

for suitable soft start time

Fig. 5. Bode plot of the loop

10

100

1 .10

3

1 .10

4

1 .10

5

1 .10

6

50

0

50

100

Loop Gain Mag (dB)

mag i

()

10

100

1 .10

3

1 .10

4

1 .10

5

1 .10

6

180

135

90

45

0

Loop Gain Phase (Degree)

phase i

()

set

5

o

zero

F

F

=

zero

F

R

C

•

=

π

2

1

V

V

F

I

C

C

R

V

G

V

C=327.95nF

R

R

C=100nF

set to

L=2.2uH