ISL6326CRZ-T Intersil, ISL6326CRZ-T Datasheet - Page 26

• Manufacturer Part Number: ISL6326CRZ-T
• Description: IC CTRLR PWM 4PHASE BUCK 40-QFN
• Manufacturer: Intersil

Specifications of ISL6326CRZ-T

• Pwm Type: Voltage Mode
• Number Of Outputs: 1
• Frequency - Max: 275kHz
• Duty Cycle: 25%
• Voltage - Supply: 4.75 V ~ 5.25 V
• Buck: Yes
• Boost: No
• Flyback: No
• Inverting: No
• Doubler: No
• Divider: No
• Cuk: No
• Isolated: No
• Operating Temperature: 0°C ~ 70°C
• Package / Case: 40-VFQFN, 40-VFQFPN
• Frequency-max: 275kHz
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

COMPENSATING LOAD-LINE REGULATED
CONVERTER
The load-line regulated converter behaves in a similar
manner to a peak-current mode controller because the two
poles at the output-filter L-C resonant frequency split with
the introduction of current information into the control loop.
The final location of these poles is determined by the system
function, the gain of the current signal, and the value of the
compensation components, R
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” on page 25.
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 three cases which follow, there is a separate set
of equations for the compensation components.
FIGURE 16. COMPENSATION CONFIGURATION FOR
R
FB
LOAD-LINE REGULATED ISL6326 CIRCUIT
V
+
-
DROOP
R
C
C
FB
2
C
(OPTIONAL)
, has already been chosen as
C
26
C
and C
IDROOP
COMP
VDIFF
FB
C
.
0
.
0
ISL6326
In Equation 35, 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
amplitude described in Electrical Specifications on page 7.
The optional capacitor C
noise away from the PWM comparator (see Figure 16). Keep
a position available for C
high-frequency capacitor of between 22pF and 150pF in
case any leading-edge jitter problem is noted.
Once selected, the compensation values in Equation 35
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 35 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 17, provides the
necessary compensation.
Case 1:
Case 2:
Case 3:
C
will not need adjustment. Keep the value of C
C
while observing the transient performance on an
R
C
-------------------
2π LC
f
R
C
-------------------
2π LC
R
C
0
C
C
C
C
C
C
>
1
1
=
=
=
=
----------------------------- -
2πC ESR
=
=
R
------------------------------------------------------------ -
(
R
0.75V
------------------------------------------------ -
R
----------------------------------- -
2πV
2
2
2π
2πV
≤
>
FB
FB
, is sometimes needed to bypass
FB
, and be prepared to install a
(
1
0.75V
f
f
)
0
0
V
--------------------------------------------
2
PP
2πf
----------------------------------- -
----------------------------------------- -
0.75 V
PP
<
PP
IN
f
0
----------------------------- -
2πC ESR
0.75V
0.75V
R
2
2π f
0
)
R
0.75 V
(
(
IN
FB
V
ESR
V
2π
FB
PP
pp
0
IN
(
f
1
0
)
V
f
IN
IN
2
0
R
(
pp
) C
IN
ESR
C
LC
f
FB
0
L
2
. Slowly increase the
L
P-P
)
LC
LC
)
is the sawtooth
C
from
May 5, 2008
(EQ. 35)
FN9262.1