ISL8102 Intersil Corporation, ISL8102 Datasheet - Page 20

• Manufacturer Part Number: ISL8102
• Description: Two-Phase Buck PWM Controller
• Manufacturer: Intersil Corporation

Due to errors in the inductance or DCR it may be necessary
to adjust the value of R
correctly. The effects of time constant mismatch can be seen
in the form of droop overshoot or undershoot during the
initial load transient spike, as shown in Figure 19. Follow the
steps below to ensure the R-C and inductor L/DCR time
constants are matched accurately.
After choosing a new value for R
necessary to adjust the value of R
load droop voltage. Use Equation 26 to obtain the new value
for R
1. Capture a transient event with the oscilloscope set to
2. Record ∆V
3. Select a new value, R
4. Replace R
about L/DCR/2 (sec/div). For example, with L = 1µH and
DCR = 1mΩ, set the oscilloscope to 500µs/div.
resistor based on the original value, R
following equation.
the error is corrected. Repeat the procedure if necessary.
R
S
ISL8102
COMP 2
.
FIGURE 18. DCR SENSING CONFIGURATION
PHASE1
PHASE2
DROOP
,
IREF
ICOMP
ISUM
=
COMP
1
and ∆V
R
COMP 1
with the new value and check to see that
COMP
,
2
C
V
as shown in Figure 19.
COMP,2
⋅
COMP
DROOP
∆
----------
∆
+
V
V
-
20
R
1
2
to match the time constants
S
COMP
, for the time constant
R
R
S
S
COMP
to obtain the desired full
I
I
L2
L1
, it will most likely be
INDUCTOR
INDUCTOR
L
L
V
COMP,1
L
(s)
DCR
DCR
-
, using the
(EQ. 27)
C
I
OUT
V
OUT
OUT
ISL8102
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 the 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,
FIGURE 20. COMPENSATION CONFIGURATION FOR
FIGURE 19. TIME CONSTANT MISMATCH BEHAVIOR
∆V
1
R
1
LOAD-LINE REGULATED ISL8102 CIRCUIT
R
2
C
2
C
(OPTIONAL)
1
2
and C
COMP
VDIFF
FB
1
.
∆V
∆I
2
ISL8102
October 19, 2005
V
I
TRAN
OUT
FN9247.0