isl6307b Intersil Corporation, isl6307b Datasheet - Page 20

• Manufacturer Part Number: isl6307b
• Description: 6-phase Vr11 Pwm Controller With 8-bit Vid Code Capable Of Precision Rds On Or Dcr Differential Current Sensing For Applications In Which Supply Voltage Is Higher Than 5v
• Manufacturer: Intersil Corporation

The magnitude of the spike is dictated by the ESR and ESL
of the output capacitors selected. By positioning the no-load
voltage level near the upper specification limit, a larger
negative spike can be sustained without crossing the lower
limit. By adding a well controlled output impedance, the
output voltage under load can effectively be level shifted
down so that a larger positive spike can be sustained without
crossing the upper specification limit.
As shown in Figure 8, a current proportional to the average
current in all active channels, I
load-line regulation resistor, R
across R
creating an output voltage droop with a steady-state value
defined as
The regulated output voltage is reduced by the droop voltage
V
derived by combining Equation 8 with the appropriate
sample current expression defined by the current sense
method employed.
Where V
programmed offset voltage, I
of the converter, R
N is the number of active channels, and R
resistor. R
R
Therefore the equivalent loadline impedance, i.e. Droop
impedance, is equal to:
Output-Voltage Offset Programming
The ISL6307B allows the designer to accurately adjust the
offset voltage. When a resistor, R
OFS to VCC, the voltage across it is regulated to 1.6V. This
causes a proportional current (I
R
regulated to 0.4V, and I
between DAC and REF, R
product (I
These functions are shown in Figure 9.
As it may be noticed in Figure 9, the OFSOUT pin must be
connected to the REF pin for this current injection to function
in ISL6307B. The current flow through R
offset at the REF pin, which is ultimately duplicated at the
output of the regulator.
V
V
R
DROOP
SENSE
OFS
DROOP
OUT
LL
=
is connected to ground, the voltage across it is
=
------------
R
. The output voltage as a function of load current is
N
FB
REF
V
depending on the sensing method.
FB
OFS
=
X
REF
I
is proportional to the output current, effectively
has a value of DCR, resistor or R
----------------- -
R
AVG
is the reference voltage, V
ISEN
R
x R
–
X
V
R
OFFSET
OFS
ISEN
FB
) is equal to the desired offset voltage.
OFS
is the sense resistor in the ISEN line,
–
REF



flows out of OFS. A resistor
I
------------ -
OUT
20
OUT
FB
, is selected so that the
6
AVG
OFS
. The resulting voltage drop
OFS
is the total output current
----------------- - R
R
, flows from FB through a
ISEN
R
) to flow into OFS. If
X
, is connected between
OFS
REF
FB
FB



is the
is the feedback
creates an
DS(ON)
(EQ. 10)
, or
(EQ. 8)
(EQ. 9)
ISL6307B
Once the desired output offset voltage has been determined,
use the following formulas to set R
For Positive Offset (connect R
For Negative Offset (connect R
Dynamic VID
Modern microprocessors need to make changes to their
core voltage as part of normal operation. They direct the
core-voltage regulator to do this by making changes to the
VID inputs during regulator operation. The power
management solution is required to monitor the DAC inputs
and respond to on-the-fly VID changes in a controlled
manner. Supervising the safe output voltage transition within
the DAC range of the processor without discontinuity or
disruption is a necessary function of the core-voltage
regulator.
The ISL6307B checks the VID inputs six times every
switching cycle. If the VID code is found to have been
changed, the controller waits half of a complete cycle before
executing a 12.5mV change. If during the half-cycle wait
period, the difference between DAC level and the new VID
code changes, no change is made. If the VID code is more
than 1-bit higher or lower than the DAC (not recommended),
R
R
OFS
OFS
FIGURE 9. OUTPUT VOLTAGE OFFSET PROGRAMMING
=
=
1.6
----------------------------- -
0.4
----------------------------- -
V
V
1.6V
OFFSET
OFFSET
×
×
WITH ISL6307B
R
R
VCC
+
-
REF
REF
0.4V
E/A
GND
+
-
FB
OFS
OFS
OFS
to VCC):
DYNAMIC
to GND):
VID D/A
ISL6307BCR
:
March 9, 2006
DAC
OFS
GND
VCC
OR
(EQ. 12)
(EQ. 11)
FN9225.0
REF
R
R
REF
OFS