ISL6314CRZ-T Datasheet, PDF (17/32 Pages) Intersil Corporation – Single-Phase Buck PWM Controller with Integrated MOSFET Drivers for Intel VR11 and AMD Applications

ISL6314
.
V_DROOP
=
R_{-----C----O-----M-----P-}
R_S
⋅
I_OUT
⋅
D
CR
(EQ. 7)
By simply adjusting the value of R_S, the load line can be set
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_COMP to compensate for the rise in DCR due to
temperature.
Note: An optional 10nF ceramic capacitor from the ISEN+
pin to the ISEN- pin is recommended to help reduce any
noise affects on the current sense amplifier due to layout
Output-Voltage Offset Programming
The ISL6314 allows the designer to accurately adjust the
offset voltage by connecting a resistor, R_OFS, from the OFS
pin to VCC or GND. When R_OFS is connected between OFS
and VCC, the voltage across it is regulated to 1.6V. This
causes a proportional current (I_OFS) to flow into the OFS pin
and out of the FB pin, providing a negative offset. If R_OFS is
connected to ground, the voltage across it is regulated to
0.3V, and I_OFS flows into the FB pin and out of the OFS pin,
providing a positive offset. 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 x R_FB).
These functions are shown in Figures 6 and 7.
Once the desired output offset voltage has been determined,
use the following formulas in Equations 8 and 9 to set R_OFS:
For Negative Offset (connect R_OFS to VCC):
R_OFS
=
--¹---^.--⁶-----^â‹---^R----^F----^B---
V_OFFSET
(EQ. 8)
For Positive Offset (connect R_OFS to GND):
R_OFS
=
--⁰---^.--³-----^â‹---^R----^F----^B---
V_OFFSET
(EQ. 9)
VDIFF
+
V_{OFS RFB}
-
VREF
E/A
FB
I_OFS
R_OFS
OFS
ISL6314
GND
+
0.3V
-
-
1.6V
+
GND
VCC
FIGURE 6. POSITIVE OFFSET OUTPUT VOLTAGE
PROGRAMMING
VDIFF
-
V_{OFS RFB}
+
VREF
E/A
FB
I_OFS
VCC
R_OFS
OFS
ISL6314
+
0.3V
-
-
1.6V
+
GND
VCC
FIGURE 7. NEGATIVE OFFSET OUTPUT VOLTAGE
PROGRAMMING
17
FN6455.2
October 8, 2009