ISL8103 INTERSIL [Intersil Corporation], ISL8103 Datasheet - Page 21

• Manufacturer Part Number: ISL8103
• Description: Three-Phase Buck PWM Controller with High Current Integrated MOSFET Drivers
• Manufacturer: INTERSIL [Intersil Corporation]

Since the system poles and zero are affected by the values
of the components that are meant to compensate them, the
solution to the system equation becomes fairly complicated.
Fortunately, there is a simple approximation that comes very
close to an optimal solution. Treating the system as though it
were a voltage-mode regulator, by compensating the L-C
poles and the ESR zero of the voltage mode approximation,
yields a solution that is always stable with very close to ideal
transient performance.
The feedback resistor, R
outlined in Load-Line Regulation Resistor. Select a target
bandwidth for the compensated system, F
bandwidth must be large enough to assure adequate
transient performance, but smaller than 1/3 of the per-
channel switching frequency. The values of the
compensation components depend on the relationships of
F
frequency. For each of the following three, there is a
separate set of equations for the compensation components.
Case 1:
Case 2:
Case 3:
0
FIGURE 19. COMPENSATION CONFIGURATION FOR
to the L-C double pole frequency and the ESR zero
R
LOAD-LINE REGULATED ISL8103 CIRCUIT
---------------------------
2π
R
C
1
---------------------------
2π
R
C
2
1
2
1
⋅
F
R
C
=
=
0
⋅
1
2
2
=
=
L C
1
>
R
------------------------------------------------------------------------------- -
(
=
=
R
L C
2π
⋅
R
------------------------------------------------ -
2π V
1
-------------------------------- -
2π C ESR
2
⋅
1
R
-------------------------------------------------------------- -
2π V
⋅
)
0.66 V
V
--------------------------------------------------------------- -
2
⋅
≤
C
⋅
1
⋅
1
0.66 V
2π F
----------------------------------------------------------- -
2
>
OSC
⋅
⋅
F
, has already been chosen as
⋅
F
C
OSC
1
(Optional)
0
F
2π F
-----------------------------------------------
⋅
1
2
0
0.66 V
⋅
OSC
⋅
0
<
0.66 V
21
⋅
⋅
⋅
-------------------------------- -
2π C ESR
⋅
0.66 V
V
0
IN
0.66 V
(
⋅
2π
OSC
⋅
IN
R
⋅
0
⋅
V
⋅
⋅
⋅
1
R
⋅
ESR
)
COMP
OSC
VDIFF
⋅
IN
2
⋅
V
1
⋅
1
IN
f
⋅
⋅
⋅
OSC
⋅
0
IN
⋅
FB
R
F
F
IN
ESR
2
0
1
⋅
⋅
0
⋅
⋅
⋅
⋅
L C
L C
C
L
0
L C
⋅
L
⋅
. The target
⋅
ISL8103
(EQ. 28)
ISL8103
In Equations 28, L is the per-channel filter inductance
divided by the number of active channels; C is the sum total
of all output capacitors; ESR is the equivalent series
resistance of the bulk output filter capacitance; and V
the peak-to-peak sawtooth signal amplitude as described in
the Electrical Specifications.
Once selected, the compensation values in Equations 28
assure a stable converter with reasonable transient
performance. In most cases, transient performance can be
improved by making adjustments to R
value of R
oscilloscope until no further improvement is noted. Normally,
C
Equations 28 unless some performance issue is noted.
The optional capacitor C
noise away from the PWM comparator (see Figure 19). Keep
a position available for C
frequency capacitor of between 22pF and 150pF in case any
leading edge jitter problem is noted.
Compensating the Converter operating without
Load-Line Regulation
The ISL8103 multi-phase converter operating without load
line regulation behaves in a similar manner to a voltage-
mode controller. This section highlights the design
consideration for a voltage-mode controller requiring external
compensation. To address a broad range of applications, a
type-3 feedback network is recommended (see Figure 20).
Figure 21 highlights the voltage-mode control loop for a
synchronous-rectified buck converter, applicable, with a
small number of adjustments, to the multi-phase ISL8103
circuit. The output voltage (V
voltage, VREF, level. The error amplifier output (COMP pin
voltage) is compared with the oscillator (OSC) modified saw-
tooth wave to provide a pulse-width modulated wave with an
amplitude of V
smoothed by the output filter (L and C). The output filter
capacitor bank’s equivalent series resistance is represented by
the series resistor E.
1
FIGURE 20. COMPENSATION CONFIGURATION FOR
will not need adjustment. Keep the value of C
C
R
3
2
3
while observing the transient performance on an
IN
NON-LOAD-LINE REGULATED ISL8103 CIRCUIT
at the PHASE node. The PWM wave is
R
R
1
2
2
2
, is sometimes needed to bypass
C
, and be prepared to install a high
2
OUT
C
1
) is regulated to the reference
COMP
VDIFF
FB
2
. Slowly increase the
ISL8103
February 15, 2006
1
from
PP
FN9246.0
is