ir3092 International Rectifier Corp., ir3092 Datasheet - Page 24

• Manufacturer Part Number: ir3092
• Description: 2 Phase Opteron, Athlon, Or Vr10.x Control Ic
• Manufacturer: International Rectifier Corp.

The maximum and minimum duty cycle adjust range of Ramp2 compared to Ramp1 has been limited to 0.5x and 2.0x of
the master’s ramp (see Figure 3.). The crossover frequency of the current share loop can be programmed with a capacitor
at the SCOMP pin so that the share loop does not interact with the output voltage loop. 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.
The SCOMP capacitor is driven by a trans-conductance stage capable of sourcing and sinking 25uA. The duty cycle of
Ramp2 inversely tracks the voltage on the SCOMP pin; if V(SCOMP) increases, Ramp2’s slope will increase and the
effective duty cycle will decrease resulting in a reduction in Phase 2’s output current. Due to the limited 25uA source
current, an SCOMP pre-charge circuit has been included to pre-condition V(SCOMP) so that the duty cycle of Ramp2 is
equal to Ramp1 prior to any GATEHX high pulses. The pre-condition circuit can source 400uA. The Equal Duty Cycle
Comparator (see Block Diagram) activates a pre-charge circuit when SS/DEL is less than 0.7V. The Error Amplifier
becomes active enabling GATEH switching when SS/DEL is above 1.3V.
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.
Resistors R
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.
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 be estimated by
Equations (13), where C
the equivalent resistance of inductor DCR.
(a) Type II compensation
VO+
VDRP
Page 24 of 37
FB
and R
RFB
RDRP
DRP
f
C
E
and R
are chosen according to Equations (9) and (10), and the selection of compensation types
VDAC
2
S
FB
FB
RCOMP
*
CE
C
+
-
CCP1
Figure11 . Voltage loop compensation network
E
are the equivalent capacitance and ESR of output capacitors respectively and R
EAOUT
(
CCOMP
G
CS
R
*
DRP
R
FB
EAOUT
R
LE
(b) Type III compensation

R
VO+
VDRP
CE
RFB1
)
RFB
RDRP
CFB
CDRP
VDAC
FB
RCOMP
+
-
CCP1
EAOUT
(13)
CCOMP
06/25/04
EAOUT
IR3092
LE
is