Application details

L6725

18/27

6.4

Compensation network

The loop is based on a voltage mode control (Figure 11). The output voltage is regulated to the

internal/external reference voltage and scaled by the external resistor divider. The error

filtered by the output filter. The modulator transfer function is the small signal transfer function

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

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:

Figure 11. Compensation Network

Cout

L

LC

⋅

=

1

ω

Cout

ESR

ESR

⋅

=

1

ω

(8)

(9)

⎟⎟⎠

⎞

⎜⎜⎝

⎛

+

⋅

⋅

=

19

18

19

18

5

1

1

C

C

C

C

R

P

ω

20

4

2

1

C

R

P

⋅

=

ω

(10)

(11)

19

5

1

1

C

R

Z

⋅

=

ω

()

4

3

20

2

1

R

R

C

Z

+

⋅

=

ω

(12)

(13)