IR3082P

bF

Page 24 of 33

01/31/05

Type II Compensation

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

output inductors matches that of the inductor, RCP and CCP can be determined by equations (27) and (28).

o

CE

E

C

PWMRMP

FB

E

E

C

CP

V

R

C

f

V

R

C

L

f

R

⋅

⋅

⋅

⋅

+

⋅

⋅

⋅

⋅

⋅

=

2

2

)

2

(

1

)

2

(

π

π

(27)

CP

E

E

CP

R

C

L

C

⋅

⋅

=

10

(28)

where LE and RCE are the equivalent output inductance and ESR of output capacitors respectively. CCP1 is optional

and may be needed in some applications to reduce the jitter caused by the high frequency noise. A ceramic

capacitor between 10pF and 220pF is usually enough.

Type III Compensation

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

output inductors matches that of the inductor, RCP and CCP can be determined by equations (29) and (30), where CE

is equivalent output capacitance.

o

PWMRMP

E

E

C

CP

V

V

C

L

f

R

⋅

⋅

⋅

⋅

=

2

)

2

(

π

(29)

CP

E

E

CP

R

C

L

C

⋅

⋅

=

10

(30)

Choose resistor RFB1 according to Equation (31), and determine CFB from Equations (32).

FB

FB

R

R

2

1

1 =

to

FB

FB

R

R

3

2

1 =

(31)

1

1

4

1

FB

C

FB

R

f

C

⋅

⋅

=

π

(32)

CCP1 is optional and may be needed in some applications to reduce the jitter caused by the high frequency noise. A

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

CURRENT SHARE LOOP COMPENSATION

The crossover frequency of the current share loop should be at least one decade lower than that of the voltage loop

in order to eliminate the interaction between the two loops. A capacitor from SCOMP to LGND is usually enough for

most of the applications. Choose the crossover frequency of current share loop (fCI) based on the crossover

frequency of voltage loop (fC), and determine the CSCOMP,

6

_

10

05

.

1

2

)]

(

2

1

[

65

.

0

⋅

⋅

⋅

⋅

⋅

⋅

⋅

⋅

+

⋅

⋅

⋅

⋅

⋅

⋅

=

CI

O

MI

O

O

E

CI

LE

ROOM

CS

O

I

PWMRMP

SCOMP

f

V

F

I

V

C

f

R

G

I

V

R

C

π

π

(33)

Where FMI is the PWM gain in the current share loop,

)

(

)

(

DAC

I

DAC

PWMRMP

O

PWMRMP

SW

PWMRMP

PWMRMP

SCOMP

V

V

V

V

V

V

f

C

R

C

−

⋅

−

−

⋅

⋅

⋅

=

(34)