8

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POWER MANAGEMENT

SC2608

(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.)

(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.

An example is given below to demonstrate the procedure

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