isl6333 Intersil Corporation, isl6333 Datasheet - Page 35

• Manufacturer Part Number: isl6333
• Description: Three-phase Buck Pwm Controller With Integrated Mosfet Drivers And Light Load Efficiency Enhancements For Intel Vr11.1 Applications
• Manufacturer: Intersil Corporation

Select a target bandwidth for the compensated system, f
The target 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
to the L-C pole frequency and the ESR zero frequency. For
each of the following three, there is a separate set of
equations for the compensation components.
In Equation 40, 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
peak-to-peak sawtooth signal amplitude, as described in the
“Electrical Specifications” on page 13.
Once selected, the compensation values in Equation 40
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
Equation 40 unless some performance issue is noted.
The optional capacitor C
noise away from the PWM comparator (see Figure 24). Keep
a position available for C
high-frequency capacitor of between 22pF and 150pF in
case any leading edge jitter problem is noted.
Case 1:
C
FIGURE 24. COMPENSATION CONFIGURATION FOR
will not need adjustment. Keep the value of C
R
C
FB
while observing the transient performance on an
LOAD-LINE REGULATED ISL6333 CIRCUIT
R
C
------------------------------- -
2 π
C
C
⋅
R
=
=
⋅
C
1
R
----------------------------------------------------- -
2 π V
L C
C
FB
⋅
2
⋅
C
(OPTIONAL)
2
⋅
2
⋅
C
, is sometimes needed to bypass
>
, and be prepared to install a
2 π f
----------------------------------------------------------
P-P
f
⋅
V
0
35
IN
IDROOP
⋅
⋅
COMP
R
VDIFF
0
FB
⋅
V
V
FB
IN
P-P
⋅
ISL6333, ISL6333A, ISL6333B, ISL6333C
f
C
0
. Slowly increase the
⋅
P-P
L C
ISL6333
⋅
is the
C
from
0
.
0
Case 3:
COMPENSATION WITHOUT LOAD-LINE REGULATION
The non load-line regulated converter is accurately modeled
as a voltage-mode regulator with two poles at the L-C
resonant frequency and a zero at the ESR frequency. A
type III controller, as shown in Figure 25, provides the
necessary compensation.
The first step is to choose the desired bandwidth, f
compensated system. Choose a frequency high enough to
assure adequate transient performance but not higher than
1/3 of the switching frequency. The type-III compensator has
an extra high-frequency pole, f
added noise rejection or to assure adequate attenuation at
the error-amplifier high-order pole and zero frequencies. A
good general rule is to choose f
higher if desired. Choosing f
Case 2:
FIGURE 25. COMPENSATION CIRCUIT WITHOUT LOAD-LINE
C
R
1
1
------------------------------- -
2 π
R
C
REGULATION
C
C
⋅
f
R
C
=
=
0
⋅
1
C
C
>
R
-------------------------------------------------------------------------------------- -
(
R
L C
2 π
------------------------------------ -
2 π C ESR
=
=
FB
FB
R
⋅
⋅
⋅
C
R
----------------------------------------------------------------- -
2 π V
⋅
)
FB
⋅
≤
C
V
---------------------------------------------------------------- -
2
⋅
2
f
PP
⋅
1
0
C
V
⋅
f
⋅
⋅
<
0
C
IN
2 π f
--------------------------------------------- -
2
HF
⋅
P-P
------------------------------------ -
2 π C ESR
(
⋅
⋅
2 π ⋅
⋅
HF
⋅
V
V
ESR
V
to be lower than 10f
HF
⋅
P-P
⋅
IN
IN
. This pole can be used for
R
⋅
V
COMP
)
0
VSEN
FB
2
IN
⋅
= 10f
1
⋅
⋅
ESR
⋅
⋅
⋅
V
R
FB
⋅
f
P-P
0
FB
C
f
2
0
0
⋅
⋅
, but it can be
⋅
⋅
L C
L
L
⋅
L C
ISL6333
⋅
0
April 10, 2008
0
, of the
(EQ. 40)
can
FN6520.0