Application details

L6731B

20/24

closed loop transfer function with the highest 0dB crossing frequency to have fastest transient

response (but always lower than fsw/10) and the highest gain in DC conditions to minimize the

load regulation error. A stable control loop has a gain crossing the 0dB axis with -20dB/decade

slope and a phase margin greater than 45°. To locate poles and zeroes of the compensation

networks, the following suggestions may be used:

●

Modulator singularity frequencies:

●

Compensation network singularity frequencies:

●

Compensation network design:

–

–

Place

ω

ω

–

Place

ω

ω

–

Place

ω

ω

–

Place

ω

–

Check the loop gain considering the error amplifier open loop gain.

Figure 12. Asymptotic Bode plot of Converter's open loop gain

Cout

L

LC

⋅

=

1

ω

Cout

ESR

ESR

⋅

=

1

ω

(13)

(14)

⎟⎟⎠

⎞

⎜⎜⎝

⎛

+

⋅

⋅

=

19

18

19

18

5

1

1

C

C

C

C

R

P

ω

20

4

2

1

C

R

P

⋅

=

ω

(15)

(16)

19

5

1

1

C

R

Z

⋅

=

ω

()

4

3

20

2

1

R

R

C

Z

+

⋅

=

ω

(17)

(18)

LC

C

Vosc

Vin

R

R

ϖ

ϖ

⋅

∆

⋅

=

3

5

(19)