ISL6313 INTERSIL [Intersil Corporation], ISL6313 Datasheet - Page 27

• Manufacturer Part Number: ISL6313
• Description: Two-Phase Buck PWM Controller with Integrated MOSFET Drivers for Intel VR11 and AMD Applications
• Manufacturer: INTERSIL [Intersil Corporation]

N is the number of phases. It is recommended that the
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 21. Follow the
steps below to ensure the R-C and inductor L/DCR time
constants are matched accurately.
Loadline Regulation Resistor
If loadline regulation is desired, the resistor on the FS pin,
R
average sense current to flow out across the loadline
regulation resistor, labeled R
value sets the desired loadline required for the application.
The desired loadline, R
where V
current I
R
1. Capture a transient event with the oscilloscope set to
2. Record ΔV1 and ΔV2 as shown in Figure 21.
3. Select new values, R
4. Replace R
T
SET
, should be connected to Ground in order for the internal
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 36.
error is corrected. Repeat the procedure if necessary.
R
FIGURE 21. TIME CONSTANT MISMATCH BEHAVIOR
1 NEW
=
(
ΔV
DROOP
FL.
----------------------------
100 10
1
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
(
⋅
I
------------- -
OCP
N
1
)
LL
⋅
to match the time constants
1(NEW)
⋅
Δ
----------
Δ
, can be calculated by Equation 37
400
--------- -
V
V
3
1
2
27
FB
OCP
, for the time constant
in Figure 7. This resistor’s
, be chosen so that it’s
1(OLD)
ΔV
ΔI
2
, using
V
I
TRAN
(EQ. 35)
(EQ. 36)
OUT
ISL6313
.
Based on the desired loadline, the loadline regulation
resistor, R
In Equation 38, R
number of active channels; DCR is the DCR of the individual
output inductors; and R
If no loadline regulation is required, the resistor on the FS
pin, R
value for R
without load-line regulation” on page 28.
IOUT Pin Resistor
A copy of the average sense current flows out of the IOUT
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 40 below to set R
desired 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
R
R
R
R
LL
IOUT
FB
APA
=
=
T
, should be connected to the VCC pin. To choose the
=
V
------------------------ -
=
R
-------------------------------------- -
DROOP
LL
V
-------------------------------- -
------------------------------- -
DCR I
I
100
FB
IOUT
FL
FB
APA TRIP
R
⋅
DCR
SET
, can be calculated from Equation 38.
N R
in this situation, please refer to “Compensation
×
(
⋅
, can be calculated from Equation 39.
⋅
10
OCP
⋅
SET
LL
N
–
6
)
is the loadline resistance; N is the
IOUT
⋅
=
⋅
--------- -
400
--------- -
400
SET
6
3
---------------------------- -
100
, placed from this pin to ground can
500mV
×
APA
is the RSET pin resistor.
10
C
–
and C
resistor to help with noise
6
=
5kΩ
C
OCP
.
APA
, the IOUT pin
APA
to get the
, should
March 5, 2007
(EQ. 37)
(EQ. 38)
(EQ. 39)
APA
(EQ. 40)
FN6448.0
to