ISL6564 Intersil Corporation, ISL6564 Datasheet - Page 23

• Manufacturer Part Number: ISL6564
• Description: Multiphase PWM Controller
• Manufacturer: Intersil Corporation

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
to the L-C pole frequency and the ESR zero frequency. For
each of the three cases which follow, there is a separate set
of equations for the compensation components.
In Equations 25, 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
Case 1:
Case 2:
Case 3:
FIGURE 18. COMPENSATION CONFIGURATION FOR
R
FB
LOAD-LINE REGULATED ISL6564 CIRCUIT
-------------------
2π LC
R
C
f
R
C
R
C
-------------------
2π LC
V
0
+
-
C
C
C
C
DROOP
C
C
R
>
1
1
C
=
=
----------------------------- -
2πC ESR
=
=
=
=
C
R
------------------------------------------------------------ -
(
R
R
0.75V
------------------------------------------------ -
----------------------------------- -
2πV
FB
2
2π
2πV
≤
>
FB
FB
FB
C
(
(OPTIONAL)
1
0.75V
f
, has already been chosen as
f
C
)
0
0
V
--------------------------------------------
PP
2
2πf
----------------------------------- -
----------------------------------------- -
0.75 V
23
<
PP
PP
IN
f
0
0.75V
----------------------------- -
2πC ESR
0.75V
R
2
2π f
0
)
R
(
0.75 V
IDROOP
IN
(
FB
V
ESR
V
2π
FB
COMP
PP
VDIFF
pp
0
IN
f
(
1
)
V
0
f
IN
IN
2
0
R
(
FB
pp
) C
IN
ESR
LC
f
FB
0
L
2
L
)
LC
0
LC
. The target
)
(EQ. 24)
0
ISL6564
resistance of the bulk output-filter capacitance; and V
the peak-to-peak sawtooth signal amplitude as described in
Figure 6 and Electrical Specifications.
The optional capacitor C
noise away from the PWM comparator (see Figure 21). Keep
a position available for C
frequency capacitor of between 22pF and 150pF in case any
leading-edge jitter problem is noted.
Once selected, the compensation values in Equations 23
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 23 unless some performance issue is noted.
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 22, 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
cause problems with too much phase shift below the system
bandwidth.
In the solutions to the compensation equations, there is a
single degree of freedom. For the solutions presented in
Equations 26, R
FIGURE 19. COMPENSATION CIRCUIT FOR ISL6564 BASED
C
will not need adjustment. Keep the value of C
C
R
1
1
C
while observing the transient performance on an
CONVERTER WITHOUT LOAD-LINE
REGULATION
FB
R
is selected arbitrarily. The remaining
FB
R
C
C
2
2
2
, is sometimes needed to bypass
, and be prepared to install a high-
C
C
HF
HF
to be lower than 10f
HF
IDROOP
. This pole can be used for
COMP
VDIFF
= 10f
FB
C
. Slowly increase the
0
, but it can be
December 27, 2004
C
0
from
0
, of the
PP
can
FN9156.2
is