ISL6322 INTERSIL [Intersil Corporation], ISL6322 Datasheet - Page 34

• Manufacturer Part Number: ISL6322
• Description: Four-Phase Buck PWM Controller with Integrated MOSFET Drivers and I2C Interface for Intel VR10, VR11, and AMD Applications
• Manufacturer: INTERSIL [Intersil Corporation]

following steps to choose the component values for the
R-C current sensing network:
If the desired overcurrent trip level, I
minimum overcurrent trip level, I
divider R-C circuit should be used to set the desired trip
level. Do the following steps to choose the component
values for the resistor divider R-C current sensing
network:
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 22. Do the
following steps to ensure the R-C and inductor L/DCR
time constants are matched accurately.
1. Choose an arbitrary value for C
2. Plug the inductor L and DCR component values, and the
3. Resistor R
1. Choose an arbitrary value for C
2. Plug the inductor L and DCR component values, the
value is 0.1µF.
value for C
calculate the value for R
value is 0.1μF.
value for C
channels N, and the desired overcurrent protection level
I
R
R
R
R
OCP
FIGURE 22. TIME CONSTANT MISMATCH BEHAVIOR
1
1
1
2
ΔV
and R
=
=
=
1
into Equations 34 and 35 to calculate the values for
-------------------------
DCR C
-------------------------------------- -
C
--------------------------------------------------------------------------------- -
C
1
1
L I
⋅
⋅
2
L
0.0375 N
(
⋅
2
.
I
1
1
⋅
OCP
OCP
should be left unpopulated.
chosen in step 1, into Equation 33 to
chosen in step 1, the number of active
1
⋅
L I
⋅
DCR 0.0375 N
⋅
1
OCP
and R
–
1
34
.
2
OCP,min
to match the time constants
I
I
⋅
OCP
OCP
1
1
OCP
. The recommended
. The recommended
)
>
=
, is greater than the
, then a resistor
I
OCP min
I
OCP min
ΔV
ΔI
2
,
,
V
I
TRAN
(EQ. 33)
(EQ. 34)
(EQ. 35)
OUT
ISL6322
Load-line Regulation Resistor
If load-line regulation is desired, the IDROOP pin should be
shorted to the FB pin in order for the internal average
sense current to flow out across the load-line regulation
resistor, labeled R
the desired load-line required for the application. The
desired load-line, R
where V
current I
Based on the desired load-line, the load-line regulation
resistor, R
Equation 40, depending on the R-C current sense circuitry
being employed. If a basic R-C sense circuit consisting of C1
and R1 is being used, use Equation 39. If a resistor divider
R-C sense circuit consisting of R1, R2, and C1 is being
used, use Equation 40.
In Equations 39 and 40:
R
N is the number of active channels,
DCR is the DCR of the individual output inductors, and
R1 and R2 are the current sense R-C resistors.
If no load-line regulation is required, the IDROOP pin should
be left open and not connected to anything. To choose the
value for R
Load-line Regulation” on page 35.
R
R
R
1. Capture a transient event with the oscilloscope set to
2. Record ΔV1 and ΔV2 as shown in Figure 22.
3. Select new values, R
4. Replace R
LL
LL
FB
FB
about L/DCR/2 (sec/div). For example, with L = 1µH and
DCR = 1mΩ, set the oscilloscope to 500µs/div.
constant resistors based on the original values, R
and R
that the error is corrected. Repeat the procedure if
necessary.
R
R
is the load-line resistance,
=
=
=
1 NEW
2 NEW
,
,
V
------------------------ -
R
--------------------------------- -
R
----------------------------------------------------------------
DROOP
FL
DROOP
LL
LL
2,OLD
I
FB
.
FL
FB
DCR
⋅
⋅
, can be calculated from Equation 39 or
N 300
N 300
=
=
in this situation, see “Compensation without
1
DCR R
⋅
⋅
R
R
, using Equation 36 and Equation 37.
and R
is the desired droop voltage at the full load
1 OLD
2 OLD
,
,
FB
⋅
LL
⋅
(
R
in Figure 6. This resistor’s value sets
, can be calculated by Equation 38,
2
2
⋅
⋅
1
with the new values and check to see
Δ
----------
Δ
Δ
----------
Δ
+
1,NEW
V
V
V
V
R
1
2
1
2
2
)
and R
2,NEW
, for the time
August 21, 2006
(EQ. 38)
(EQ. 39)
(EQ. 40)
(EQ. 36)
(EQ. 37)
1,OLD
FN6328.0