isl6333 Intersil Corporation, isl6333 Datasheet - Page 34

• 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

desired overcurrent trip level, I
30% larger then the maximum load current expected.
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 23. Follow the
steps below to ensure the R-C and inductor L/DCR time
constants are matched accurately.
.
Loadline Regulation Resistor
If load line regulation is desired on the ISL6333 and
ISL6333A, the IDROOP pin should be connected to the FB
pin in order for the internal average sense current to flow
out across the loadline regulation resistor, labeled R
Figure 7. The ISL6333B and ISL6333C always have the
load line regulation enabled. The R
the desired loadline required for the application. The
desired loadline, R
where V
current I
R
R
1. Capture a transient event with the oscilloscope set to
2. Record ΔV1 and ΔV2 as shown in Figure 23.
3. Select new values, R
4. Replace R
SET
LL
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
Equation 35.
error is corrected. Repeat the procedure if necessary.
R
FIGURE 23. TIME CONSTANT MISMATCH BEHAVIOR
=
1 NEW
=
(
ΔV
V
------------------------ -
DROOP
FL
DROOP
----------------------------
100 10
1
I
.
FL
DCR
)
×
=
1
R
with the new value and check to see that the
is the desired droop voltage at the full load
–
6
1 OLD
(
LL
⋅
I
------------- -
OCP
, can be calculated by Equation 36
N
1
)
⋅
to match the time constants
1(NEW)
⋅
Δ
----------
Δ
400
--------- -
V
V
3
1
2
34
OCP
, for the time constant
, be chosen so that it’s
FB
ISL6333, ISL6333A, ISL6333B, ISL6333C
resistor value sets
1(OLD)
ΔV
ΔI
2
, using
(EQ. 36)
V
I
TRAN
(EQ. 34)
(EQ. 35)
OUT
FB
in
Based on the desired loadline, the loadline regulation
resistor, R
In Equation 37, R
number of active channels; DCR is the DCR of the individual
output inductors; and R
If no loadline regulation is required on the ISL6333 and
ISL6333A, the IDROOP pin should be left unconnected. To
choose the value for R
“Compensation Without Load-line Regulation” on page 35.
IMON Pin Resistor
A copy of the average sense current flows out of the IMON
pin, and a resistor, R
be used to set the overcurrent protection trip level. Based on
the desired overcurrent trip threshold, I
resistor, R
APA Pin Component Selection
A 100µA current flows into the APA pin and across R
set the APA trip level. A 1000pF capacitor, C
also be placed across the R
immunity. Use Equation 39 to set R
APA trip level. An APA trip level of 500mV is recommended
for most applications.
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.
COMPENSATION WITH LOAD-LINE REGULATION
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.
R
R
R
IMON
FB
APA
=
=
R
-------------------------------------- -
=
LL
V
-------------------------------- -
IMON
100
FB
------------------------------- -
DCR I
APA TRIP
R
⋅
DCR
, can be calculated from Equation 37.
N R
SET
×
(
⋅
, can be calculated from Equation 38.
⋅
10
OCP
SET
⋅
LL
–
N
6
)
IMON
is the loadline resistance; N is the
=
⋅
⋅
--------- -
400
FB
3.381
-------------- -
SET
400
3
---------------------------- -
100
500mV
, placed from this pin to ground can
in this situation, please refer to
×
APA
is the RSET pin resistor.
10
C
–
and C
resistor to help with noise
6
=
APA
5kΩ
OCP
C
. See Figure 24.
to get the desired
, the IMON pin
APA
, should
April 10, 2008
(EQ. 37)
(EQ. 38)
APA
(EQ. 39)
FN6520.0
to