ISL8103 INTERSIL [Intersil Corporation], ISL8103 Datasheet - Page 13

• Manufacturer Part Number: ISL8103
• Description: Three-Phase Buck PWM Controller with High Current Integrated MOSFET Drivers
• Manufacturer: INTERSIL [Intersil Corporation]

lumped quantity, as shown in Figure 7. The channel current,
I
Equation 6 shows the s-domain equivalent voltage, V
across the inductor.
The inductor DCR is important because the voltage dropped
across it is proportional to the channel current. By using a
simple R-C network and a current sense amplifier, as shown
in Figure 7, the voltage drop across all of the inductors DCRs
can be extracted. The output of the current sense amplifier,
V
currents I
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
V
V
L
V
DROOP
DROOP
, flowing through the inductor, passes through the DCR.
DROOP
L
s ( )
V
ISL8103
DROOP
=
+
-
s ( )
, can be shown to be proportional to the channel
I
FIGURE 7. DCR SENSING CONFIGURATION
L1
L
=
PHASE1
PHASE2
DROOP
⋅
=
, I
R
-------------------- - I
(
IREF
s L
ICOMP
------------------------------------------------------------------------- -
(
COMP
L2
ISUM
s R COMP C COMP
R
⋅
⋅
, and I
S
DROOP
+
DCR
⋅


DROOP
OUT
-------------
DCR
s L
OUT
L3
⋅
)
⋅
C
, shown in Equation 7.
is equal to the sum of the voltage
.
+
SUM
⋅
(Optional)
C
1
DCR
COMP


is therefore proportional to the
13
R
S
+
1
R
R
)
S
COMP
⋅
R COMP
-----------------------
I
I
L2
L1
INDUCTOR
INDUCTOR
R S
L2
L1
V
L
(s)
⋅
(
DCR
DCR
I
L1
-
+
I
L2
(EQ. 6)
L
+
(EQ. 8)
C
,
(EQ. 7)
I
I
OUT
V
L3
OUT
OUT
) DCR
⋅
ISL8103
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 ISL8103 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
OFS
V
R
COMP
OFS
OFS
+
-
FIGURE 8. POSITIVE OFFSET OUTPUT VOLTAGE
VDIFF
x R
GND
to compensate for the rise in DCR due to
R
I
OFS
1
1
OFS
). These functions are shown in Figures 8 and 9.
FB
PROGRAMMING
ISL8103
VREF
OFS
OFS
is connected to ground, the
OFS
is connected between OFS
S
, the load line can be set
) to flow into the OFS pin
OFS
E/A
GND
OFS
+
-
, from the OFS
0.5V
flows into the
February 15, 2006
VCC
FN9246.0
+
-
1.5V