ISL6326 Intersil Corporation, ISL6326 Datasheet - Page 26

• Manufacturer Part Number: ISL6326
• Description: 4-Phase PWM Controller
• Manufacturer: Intersil Corporation

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two or more times to achieve optimal thermal balance
between all channels.
Load-Line Regulation Resistor
The load-line regulation resistor is labelled R
Its value depends on the desired loadline requirement of the
application.
The desired loadline can be calculated by the following
equation:
where I
and VR
load condition.
Based on the desired loadline R
resistor can be calculated by the following equation:
where N is the active channel number, R
resistor connected to the ISEN+ pin, and R
resistance of the current sense element, either the DCR of
the inductor or R
If one or more of the current sense resistors are adjusted for
thermal balance, as in Equation 31, the load-line regulation
resistor should be selected based on the average value of
the current sensing resistors, as given in the following
equation:
where R
the n
Compensation
The two opposing goals of compensating the voltage
regulator are stability and speed. Depending on whether the
regulator employs the optional load-line regulation as
described in Load-Line Regulation, there are two distinct
methods for achieving these goals.
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.
R
R
R
LL
FB
FB
=
th
=
=
V
------------------------ -
ISEN+ pin.
FL
N R
--------------------------------- -
R
----------
DROOP
R
ISEN(n)
DROOP
LL
X
I
is the full load current of the specific application,
FL
ISEN
R
∑
n
X
R
R
is the desired voltage droop under the full
ISEN n ( )
is the current sensing resistor connected to
LL
SENSE
depending on the sensing method.
26
C
LL
and C
, the loadline regulation
C
.
ISEN
X
FB
is the
is the sense
in Figure 5.
(EQ. 33)
(EQ. 34)
(EQ. 32)
ISL6326
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
perHchannel 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
IDROOP
COMP
VDIFF
FB
0
. The target
April 21, 2006
FN9262.0
0