IR3094PBF

Page 21 of 29

09/26/05

RCP

CCP1

EAOUT

CCP

RFB

RDRP

VO+

VDRP

VDAC

+

-

EAOUT

FB

FB

CFB

CDRP

RCP

EAOUT

CCP1

CCP

RFB

RDRP

VO+

VDRP

VDAC

FB

+

-

EAOUT

RFB1

(

a) Type II compensation

(b) Type III compensation

Figure 9. Voltage loop compensation networks

Type II Compensation for Voltage Droop Applications

Determine the compensation at no load, the worst case condition. Choose the crossover frequency fc between 1/10

and 1/5 of the switching frequency per phase. Assume the time constant of the resistor and capacitor across the

the equivalent inductance of output inductors and the equivalent capacitance of output capacitors respectively.

2

2

)

*

*

*

2

(

1

*

5

)

2

(

C

C

I

FB

E

E

C

CP

R

C

f

V

R

C

L

f

R

S

S



(16)

CP

E

E

CP

R

C

L

C

10

(17)

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

Type III Compensation for Voltage Droop 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 the

LE

FB

CS

E

DRP

C

R

R

G

C

R

f

*

*

2

1

S

(18)

S

T

180

)

5

.

0

tan(

90

1

 A

C

(19)

Choose the desired crossover frequency fc around fc1 estimated by (18) 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 /Dec

and (22).

VREF

VREF