IR3523

Page 29 of 37

June 20, 2008

Type III Compensation for AVP Applications

Determine the compensation at no load, the worst case condition. Assume the time constant of the resistor and

capacitor across the output inductors matches that of the inductor, the crossover frequency and phase margin of

LE

FB

CS

E

DRP

C

R

R

G

C

R

f

∗

∗

=

*

*

2

1

π

(25)

π

θ

180

)

5

.

0

tan(

90

1

∗

−

=

A

C

(26)

Choose the desired crossover frequency fc around fc1 estimated by (25) or choose fc between 1/10 and 1/5 of

the switching frequency per phase, and select the components to ensure the slope of close loop gain is -20dB

(28) and (29).

FB

FB

R

R

2

1

to

FB

FB

R

R

3

2

(27)

1

4

1

FB

C

FB

R

f

C

∗

∗

=

π

(28)

DRP

FB

FB

FB

DRP

R

C

R

R

C

∗

+

=

)

(

1

(29)

I

FB

E

E

C

CP

V

R

C

L

f

R

5

)

2

(

2

∗

∗

∗

∗

∗

=

π

(30)

CP

E

E

CP

R

C

L

C

∗

∗

=

10

(31)

A ceramic capacitor between 10pF and 220pF is usually enough.

Type III Compensation for Non-AVP Applications

the switching frequency per phase and select the desired phase margin θc. Calculate K factor from (32), and

determine the component values based on (33) to (37),

)]

5

.

1

180

(

4

tan[

+

∗

=

C

K

θ

π

(32)

K

V

f

C

L

R

R

I

C

E

E

FB

CP

∗

∗

∗

∗

∗

∗

=

5

)

2

(

2

π

(33)

CP

C

CP

R

f

K

C

∗

∗

=

π

2

(34)

CP

C

CP

R

K

f

C

∗

∗

∗

=

π

2

1

1

(35)