isl6566a Intersil Corporation, isl6566a Datasheet - Page 14

• Manufacturer Part Number: isl6566a
• Description: Three-phase Buck Pwm Controller With Two Integrated Mosfet Drivers And One External Driver Signal
• Manufacturer: Intersil Corporation

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 7 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.
V
V
DROOP
COMP
DROOP
DROOP
To External Driver
V
PHASE Pin
DROOP
s ( )
ISL6566A
to compensate for the rise in DCR due to
, can be shown to be proportional to the channel
-
+
FIGURE 7. DCR SENSING CONFIGURATION
L1
=
PHASE2
PHASE1
=
, I
R
-------------------- - I
------------------------------------------------------------------------- -
(
s R COMP C COMP
ICOMP
COMP
L2
ISUM
⋅
R
IREF
, and I
S
PHASE3
DROOP


-------------
DCR
s L
⋅
⋅
DROOP
OUT
⋅
OUT
L3
+
1
, shown in Equation 6.
is equal to the sum of the voltage


.
(optional)
R
⋅
S
DCR
C
+
is therefore proportional to the
14
R
COMP
1
S
)
⋅
R
-----------------------
COMP
R
S
R S
S
, the load line can be set
R
I
I
I
L2
L1
COMP
L3
INDUCTOR
INDUCTOR
INDUCTOR
⋅
(
L
L
L
I
L1
V
L
+
(s)
I
L2
DCR
DCR
DCR
-
+
I
L3
) DCR
⋅
(EQ. 6)
(EQ. 7)
C
I
OUT
V
OUT
OUT
ISL6566A
Note: An optional 10nF ceramic capacitor from the ISUM pin
to the IREF pin is recommended to help reduce any noise
affects on the current sense amplifier due to layout.
Output-Voltage Offset Programming
The ISL6566A 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
R
FB
OFS
OFS
+
FIGURE 8. POSITIVE OFFSET OUTPUT VOLTAGE
-
). These functions are shown in Figures 8 and 9.
VDIFF
GND
R
I
OFS
FB
OFS
FB
PROGRAMMING
ISL6566A
VREF
OFS
OFS
is connected to ground, the
OFS
is connected between OFS
) to flow into the OFS pin
OFS
E/A
GND
OFS
+
-
, from the OFS
0.5V
flows into the
July 27, 2005
VCC
OFS
FN9200.2
+
-
1.5V
x