IR3093

Page 26 of 39

07/15/04

SETBIAS

FD

BIASOUT

SET

I

V

V

R



(15)

Compensation of the Current Share Loop

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 22nF capacitor from SCOMP to LGND is good

for most of the applications. If necessary have a 1k resistor in series with the Csc to make the current loop a little

bit faster.

Compensation of Voltage Loop

The adaptive voltage positioning is used in the computer applications to meet the load line requirements. Like

current mode control, the adaptive voltage positioning loop introduces extra zero to the voltage loop and splits the

double poles of the power stage, which make the voltage loop compensation much easier.

types depends on the capacitors used. For the applications using Electrolytic, Polymer or AL-Polymer capacitors,

type II compensation shown in Figure 11 (a) is usually enough. While for the applications with only low ESR

ceramic capacitors, type III compensation shown in Figure 11 (b) is preferred.

(a) Type II compensation

(b) Type III compensation

Figure 11 . Voltage loop compensation network

Type II Compensation

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 of the voltage loop can

)

*

(

*

2

CE

LE

FB

CS

E

DRP

C

R

R

R

G

C

R

f



S

(16)

frequency and transient load response. Choose the desired crossover frequency fc1 around fc estimated by

CFB

CDRP

RCOMP

EAOUT

CCP1

CCOMP

RFB

RDRP

VO+

VDRP

VDAC

FB

+

-

EAOUT

RFB1

RCOMP

CCP1

EAOUT

CCOMP

RFB

RDRP

VO+

VDRP

VDAC

+

-

EAOUT

FB

FB