ISL6310 Datasheet, PDF (8/27 Pages) Intersil Corporation – Two-Phase Buck PWM Controller with High Current Integrated MOSFET Drivers

ISL6310
These pins are internally pulled high, to approximately 1.2V,
by 40µA (typically) internal current sources; the internal
pull-up current decreases to 0 as the REF0 and REF1
voltages approach the internal pull-up voltage. Both REF0
and REF1 pins are compatible with external pull-up voltages
not exceeding the IC’s bias voltage (VCC).
VSEN and RGND (Pins 8, 7)
VSEN and RGND are inputs to the precision differential
remote-sense amplifier and should be connected to the sense
pins of the remote load.
ICOMP, ISUM, and IREF (Pins 10, 12, 13)
ISUM, IREF, and ICOMP are the DCR current sense
amplifier’s negative input, positive input, and output
respectively. For accurate DCR current sensing, connect a
resistor from each channel’s phase node to ISUM and
connect IREF to the summing point of the output inductors,
roughly VOUT. A parallel R-C feedback circuit connected
between ISUM and ICOMP will then create a voltage from
IREF to ICOMP proportional to the voltage drop across the
inductor DCR. This voltage is referred to as the droop voltage
and is added to the differential remote-sense amplifier’s
output
An optional 0.001µF to 0.01µF ceramic capacitor can be
placed from the IREF pin to the ISUM pin to help reduce
common mode noise that might be introduced by the layout.
DROOP (Pin 11)
This pin enables or disables droop. Tie this pin to the ICOMP
pin to enable droop. To disable droop, tie this pin to the IREF
pin.
VDIFF (Pin 6)
VDIFF is the output of the differential remote-sense amplifier.
The voltage on this pin is equal to the difference between
VSEN and RGND added to the difference between IREF and
ICOMP. VDIFF therefore represents the VOUT voltage plus
the droop voltage.
FB and COMP (Pins 5, 4)
The internal error amplifier’s inverting input and output
respectively. FB is connected to VDIFF through an external
R or R-C network depending on the desired type of
compensation (Type II or III). COMP is tied back to FB
through an external R-C network to compensate the
regulator.
DAC (Pin 32)
The DAC pin is the direct output of the internal DAC. This pin
is connected to REF pin using 1kΩ to 5kΩ resistor, This pin
can be left open if an external reference is used.
REF (Pin 1)
The REF input pin is the positive input of the error amplifier.
This pin can be connected to the DAC pin using a resistor
(1kΩ to 5kΩ) when the internal DAC voltage is used as the
reference voltage. When an external voltage reference is used,
it must be connected directly to the REF pin, while the DAC pin
is left unconnected. The output voltage will be regulated to the
voltage at the REF pin unless this voltage is greater than the
voltage at the DAC pin. If an external reference is used at this
pin, its magnitude cannot exceed 1.75V.
A capacitor is used between the REF pin and ground to
smooth the DAC voltage during soft-start.
OFST (Pin 2)
The OFST pin provides a means to program a DC current for
generating an offset voltage across the resistor between FB
and VDIFF. The offset current is generated via an external
resistor and precision internal voltage references. The polarity
of the offset is selected by connecting the resistor to GND or
VCC. For no offset, the OFST pin should be left unconnected.
OCSET (Pin 9)
This is the overcurrent set pin. Placing a resistor from OCSET
to ICOMP, allows a 100μA current to flow out of this pin,
producing a voltage reference. Internal circuitry compares the
voltage at OCSET to the voltage at ISUM, and if ISUM ever
exceeds OCSET, the overcurrent protection activates.
ISEN1, ISEN2 (Pins 26, 16)
These pins are used for balancing the channel currents by
sensing the current through each channel’s lower MOSFET
when it is conducting. Connect a resistor between the ISEN1
and ISEN2 pins and their respective phase node. This
resistor sets a current proportional to the current in the lower
MOSFET during its conduction interval.
UGATE1 and UGATE2 (Pins 25, 17)
Connect these pins to the upper MOSFETs’ gates. These
pins are used to control the upper MOSFETs and are
monitored for shoot-through prevention purposes. Maximum
individual channel duty cycle is limited to 66%.
BOOT1 and BOOT2 (Pins 24,18)
These pins provide the bias voltage for the upper MOSFETs’
drives. Connect these pins to appropriately-chosen external
bootstrap capacitors. Internal bootstrap diodes connected to
the PVCC pins provide the necessary bootstrap charge.
PHASE1 and PHASE2 (Pins 23, 19)
Connect these pins to the sources of the upper MOSFETs.
These pins are the return path for the upper MOSFETs’
drives.
LGATE1 and LGATE2 (Pins 27, 14)
These pins are used to control the lower MOSFETs and are
monitored for shoot-through prevention purposes. Connect
these pins to the lower MOSFETs’ gates. Do not use external
series gate resistors as this might lead to shoot-through.
8
FN9209.4
August 7, 2008