IR3081 International Rectifier Corp., IR3081 Datasheet - Page 22

• Manufacturer Part Number: IR3081
• Description: Xphasetm Vr 10 Control Ic
• Manufacturer: International Rectifier Corp.

If the over temperature setting voltage is higher than the phase delay setting voltage, VBIAS*RA
HOTSET pin between R
respectively. Pre-select R
Bootstrap Capacitor C
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 adopted 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 R
depends on the output capacitors used in the converter. For the applications using Electrolytic, Polymer or AL-
Polymer capacitors and running at lower frequency, type II compensation shown in Figure 12(a) is usually enough.
While for the applications using only ceramic capacitors and running at higher frequency, type III compensation
shown in Figure 12(b) is preferred.
For applications where AVP is not required, the compensation is the same as for the regular voltage mode control.
For converter using Polymer, AL-Polymer, and ceramic capacitors, which have much higher ESR zero frequency,
type III compensation is required as shown in Figure 12(b) with R
Type II Compensation for AVP 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
output inductors matches that of the inductor, and determine R
and C
respectively.
Page 22 of 39
VO+
VDRP
E
are the equivalent inductance of output inductors and the equivalent capacitance of output capacitors
FB
and R
RFB
RDRP
(a) Type II compensation
R
R
DRP
PHASEx
PHASEx
BST
PHASEx1
are chosen according to Equations (15) and (16), and the selection of compensation types
PHASEx1
3
2
VDAC
=
=
FB
FB
RA
RCP
(
V
HOTSET
PHASEx
and R
,
Figure 12. Voltage loop compensation network
+
-
V
CCP1
BIAS
EAOUT
∗
PHASEx2
−
V
−
RA
V
BIAS
V
CCP
BIAS
HOTSET
PHASEx
*
−
R
and connect RMPIN+ or RMPIN- between R
V
PHASEx
HOTSET
∗
EAOUT
V
BIAS
1
)
∗
R
VO+
VDRP
PHASEx
RFB1
CP
DRP
(b) Type III compensation
1
and C
RFB
RDRP
CFB
CDRP
and C
CP
DRP
from Equations (27) and (28), where L
VDAC
FB
removed.
RCP
+
-
CCP1
EAOUT
CCP
(25)
(26)
PHASEx2
EAOUT
10/01
PHASEx
IR3081
and R
/04
, connect
PHASEx3
E