IR3082PbF

Page 23 of 33

01/31/05

)

1

(

)

(

1

2

PHASEx

BIAS

PHASEx

HOTSET

BIAS

PHASEx

PHASEx

RA

V

R

V

V

RA

R

−

⋅

⋅

−

⋅

=

(23)

)

1

(

1

3

PHASEx

BIAS

PHASEx

HOTSET

PHASEx

RA

V

R

V

R

−

⋅

⋅

=

(24)

If the over temperature setting voltage is higher than the phase delay setting voltage, VBIAS times RAPHASEx,

connect HOTSET pin between RPHASEx1 and RPHASEx2 and connect RMPIN+ or RMPIN- between RPHASEx2 and

RPHASEx3 respectively. Pre-select RPHASEx1,

HOTSET

BIAS

PHASEx

BIAS

PHASEx

HOTSET

PHASEx

V

V

R

V

RA

V

R

−

⋅

⋅

−

=

1

2

)

(

(25)

HOTSET

BIAS

PHASEx

BIAS

PHASEx

PHASEx

V

V

R

V

RA

R

−

⋅

⋅

=

1

3

(26)

Bootstrap Capacitor CBST

Depending on the duty cycle and gate drive current of the phase IC, a 0.1uF to 1uF capacitor is needed for the

bootstrap circuit.

Decoupling Capacitors for Phase IC

0.1uF-1uF decoupling capacitors are required at VCC and VCCL pins of phase ICs.

VOLTAGE LOOP COMPENSATION

The adaptive voltage positioning (AVP is usually used in the computer applications to improve the transient

response and reduce the power loss at heavy load. 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.

Resistors RFB and RDRP are chosen according to Equations (15) and (16), and the selection of compensation types

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

compensation shown in Figure 18 (a) is usually enough. While for the applications with only ceramic capacitors,

type III compensation shown in Figure 18 (b) is preferred.

EAOUT

FB

VDAC

VO+

VDRP

-

+

EAOUT

RFB

RDRP

RCP

CCP

CCP1

EAOUT

FB

VDAC

VO+

VDRP

-

+

EAOUT

RFB1

CFB

RFB

RDRP

RCP

CCP

CCP1

(a) Type II compensation

(b) Type III compensation

Figure 18. Voltage loop compensation network