ISL8102 Intersil Corporation, ISL8102 Datasheet - Page 13

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

If the R-C network components are selected such that the
R-C time constant matches the inductor L/DCR time
constant, then V
drops across the individual DCRs, multiplied by a gain. As
Equation 8 shows, V
total output current, I
By simply adjusting the value of R
to any level, giving the converter the right amount of droop at
all load currents. It may also be necessary to compensate for
any changes in DCR due to temperature. These changes
cause the load line to be skewed, and cause the R-C time
constant to not match the L/DCR time constant. If this
becomes a problem a simple negative temperature
coefficient resistor network can be used in the place of
R
temperature.
Output Voltage Offset Programming
The ISL8102 allows the designer to accurately adjust the
offset voltage by connecting a resistor, R
pin to VCC or GND. When R
and VCC, the voltage across it is regulated to 1.5V. This
causes a proportional current (I
and out of the FB pin. If R
voltage across it is regulated to 0.5V, and I
FB pin and out of the OFS pin. The offset current flowing
through the resistor between VDIFF and FB will generate the
desired offset voltage which is equal to the product (I
R
V
COMP
1
DROOP
). These functions are shown in Figures 8 and 9.
V
ISL8102
DROOP
+
-
to compensate for the rise in DCR due to
FIGURE 7. DCR SENSING CONFIGURATION
=
PHASE1
PHASE2
DROOP
R
-------------------- - I
IREF
ICOMP
COMP
ISUM
R
S
DROOP
⋅
DROOP
OUT
OUT
C
is equal to the sum of the voltage
.
SUM
⋅
(Optional)
OFS
C
DCR
COMP
OFS
is therefore proportional to the
13
R
S
is connected to ground, the
OFS
is connected between OFS
R
R
S
S
COMP
, the load line can be set
) to flow into the OFS pin
I
I
L2
L1
INDUCTOR
INDUCTOR
L
L
OFS
V
OFS
L
(s)
, from the OFS
DCR
DCR
-
flows into the
OFS
(EQ. 8)
C
I
OUT
V
OUT
OUT
x
ISL8102
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
R
R
OFS
OFS
V
R
V
R
FIGURE 8. POSITIVE OFFSET OUTPUT VOLTAGE
FIGURE 9. NEGATIVE OFFSET OUTPUT VOLTAGE
OFS
OFS
OFS
OFS
+
-
+
-
VDIFF
VDIFF
VCC
=
=
I
--------------------------
V
--------------------------
V
OFS
GND
R
R
I
0.5 R
1.5 R
OFS
OFFSET
OFFSET
1
1
OFS
OFS
FB
FB
⋅
⋅
PROGRAMMING
PROGRAMMING
1
1
ISL8102
ISL8102
VREF
VREF
OFS
OFS
OFS
to GND):
to VCC):
:
E/A
GND
E/A
GND
+
+
-
-
0.5V
0.5V
October 19, 2005
(EQ. 9)
VCC
VCC
(EQ. 10)
FN9247.0
+
+
-
-
1.5V
1.5V