ISL6326 Datasheet, PDF (9/30 Pages) Intersil Corporation – 4-Phase PWM Controller with 8-Bit DAC Code Capable of Precision rDS ON or DCR Differential Current Sensing

ISL6326
Functional Pin Description
VCC
Supplies the power necessary to operate the chip. The
controller starts to operate when the voltage on this pin
exceeds the rising POR threshold and shuts down when the
voltage on this pin drops below the falling POR threshold.
Connect this pin directly to a +5V supply.
GND
Bias and reference ground for the IC. The bottom metal base
of ISL6326 is the GND.
EN_PWR
This pin is a threshold-sensitive enable input for the
controller. Connecting the 12V supply to EN_PWR through
an appropriate resistor divider provides a means to
synchronize power-up of the controller and the MOSFET
driver ICs. When EN_PWR is driven above 0.875V, the
ISL6326 is active depending on status of EN_VTT, the
internal POR, and pending fault states. Driving EN_PWR
below 0.745V will clear all fault states and prime the ISL6326
to soft-start when re-enabled.
EN_VTT
This pin is another threshold-sensitive enable input for the
controller. It’s typically connected to VTT output of VTT
voltage regulator in the computer mother board. When
EN_VTT is driven above 0.875V, the ISL6326 is active
depending on status of EN_PWR, the internal POR, and
pending fault states. Driving EN_VTT below 0.745V will clear
all fault states and prime the ISL6326 to soft-start when
re-enabled.
FS
Use this pin to set up the desired switching frequency. A
resistor, placed from FS to ground will set the switching
frequency. The relationship between the value of the resistor
and the switching frequency will be described by an
approximate equation.
SS
Use this pin to set up the desired start-up oscillator
frequency. A resistor, placed from SS to ground will set up
the soft-start ramp rate. The relationship between the value
of the resistor and the soft-start ramp up time will be
described by an approximate equation.
VID7, VID6, VID5, VID4, VID3, VID2, VID1 and VID0
These are the inputs to the internal DAC that generates the
reference voltage for output regulation. Connect these pins
either to open-drain outputs with or without external pull-up
resistors or to active pull-up outputs. All VID pins have 40µA
internal pull-up current sources that diminish to zero as the
voltage rises above the logic-high level. These inputs can be
pulled up externally as high as VCC plus 0.3V.
VRSEL
use this pin to select internal VID code. When it is connected
to GND, the extended VR10 code is selected. When it’s
floated or pulled to high, VR11 code is selected. This input
can be pulled up as high as VCC plus 0.3V.
VDIFF, VSEN, and RGND
VSEN and RGND form the precision differential remote-
sense amplifier. This amplifier converts the differential
voltage of the remote output to a single-ended voltage
referenced to local ground. VDIFF is the amplifier’s output
and the input to the regulation and protection circuitry.
Connect VSEN and RGND to the sense pins of the remote
load.
FB and COMP
Inverting input and output of the error amplifier respectively.
FB can be connected to VDIFF through a resistor. A properly
chosen resistor between VDIFF and FB can set the load line
(droop), when IDROOP pin is tied to FB pin. The droop scale
factor is set by the ratio of the ISEN resistors and the
inductor DCR or the dedicated current sense resistor. COMP
is tied back to FB through an external R-C network to
compensate the regulator.
DAC and REF
The DAC pin is the output of the precision internal DAC
reference. The REF pin is the positive input of the Error
Amp. In typical applications, a 1kΩ, 1% resistor is used
between DAC and REF to generate a precision offset
voltage. This voltage is proportional to the offset current
determined by the offset resistor from OFS to ground or
VCC. A capacitor is used between REF and ground to
smooth the voltage transition during Dynamic VID™
operations.
PWM1, PWM2, PWM3, PWM4
Pulse width modulation outputs. Connect these pins to the
PWM input pins of the Intersil driver IC. The number of
active channels is determined by the state of PWM3 and
PWM4. Tie PWM3 to VCC to configure for 2-phase
operation. Tie PWM4 to VCC to configure for 3-phase
operation.
ISEN1+, ISEN1-; ISEN2+, ISEN2-; ISEN3+, ISEN3-;
ISEN4+, ISEN4-
The ISEN+ and ISEN- pins are current sense inputs to
individual differential amplifiers. The sensed current is used
for channel current balancing, overcurrent protection, and
droop regulation. Inactive channels should have their
respective current sense inputs left open (for example, open
ISEN4+ and ISEN4- for 3-phase operation).
For DCR sensing, connect each ISEN- pin to the node
between the RC sense elements. Tie the ISEN+ pin to the
other end of the sense capacitor through a resistor, R_ISEN.
The voltage across the sense capacitor is proportional to the
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FN9262.1
May 5, 2008