ISL6432 Datasheet, PDF (5/12 Pages) Intersil Corporation – PWM and Triple Linear Power Controller for Home Gateway Applications

ISL6432
Functional Pin Descriptions
VCC (Pin 11)
Provide a well decoupled 5V bias supply for the IC to this
pin. This pin also provides the gate bias charge for the lower
MOSFET controlled by the PWM section of the IC, as well as
the base current drive for the linear regulators’ external
bipolar transistors. The voltage at this pin is monitored for
Power-On Reset (POR) purposes.
GND (Pin 5)
Signal ground for the IC. All voltage levels are measured with
respect to this pin.
PGND (Pin 9)
This is the power ground connection. Tie the synchronous
PWM converter’s lower MOSFET source to this pin.
BOOT (Pin 7)
Connect a suitable capacitor (0.47µF recommended) from
this pin to PHASE. This bootstrap capacitor supplies UGATE
driver the energy necessary to turn and hold the upper
MOSFET on.
OCSET (Pin 12)
Connect a resistor from this pin to the drain of the upper
PWM MOSFET. This resistor, an internal 40µA current
source (typical), and the upper MOSFET’s on-resistance set
the converter overcurrent trip point. An overcurrent trip
cycles the soft-start function.
The voltage at this pin is monitored for power-on reset (POR)
purposes and pulling this pin below 1.25V with an open
drain/collector device will shutdown the switching controller.
PHASE (Pin 6)
Connect the PHASE pin to the PWM converter’s upper
MOSFET source. This pin is used to monitor the voltage
drop across the upper MOSFET for overcurrent protection.
UGATE (Pin 8)
Connect UGATE pin to the PWM converter’s upper MOSFET
gate. This pin provides the gate drive for the upper MOSFET.
LGATE (Pin 10)
Connect LGATE to the PWM converter’s lower MOSFET
gate. This pin provides the gate drive for the lower MOSFET.
COMP and FB (Pins 4, 3)
COMP and FB are the available external pins of the PWM
converter error amplifier. The FB pin is the inverting input of the
error amplifier. Similarly, the COMP pin is the error amplifier
output. These pins are used to compensate the voltage-mode
control feedback loop of the synchronous PWM converter.
DRIVE2, 3, 4 (Pins 1, 15, 13)
Connect these pins to the base terminals of external bipolar
NPN transistors. These pins provide the base current drive
for the regulator pass transistors.
FB2, 3, 4 (Pins 2, 16, 14)
Connect the output of the corresponding linear regulators to
these pins through properly sized resistor dividers. The
voltage at these pins is regulated to 0.8V. These pins are
also monitored for undervoltage events.
Quickly pulling and holding any of these pins above 1.25V
(using diode-coupled logic devices) shuts off the respective
regulators. Releasing these pins from the pull-up voltage
initiates a soft-start sequence on the respective regulator.
Description
Operation
The ISL6432 monitors and precisely controls 4 output
voltage levels (Refer to Block and Simplified Power System
Diagrams, and Typical Application Schematic). The IC has a
synchronous PWM controller and three linear controllers.
The PWM controller drives 2 MOSFETs (Q1 and Q2) in a
synchronous-rectified buck converter configuration and
regulates the output voltage to a level programmed by a
resistor divider. The linear controllers are designed to
regulate three more of the communication chip set
voltages. All linear controllers are designed to employ
external NPN bipolar pass transistors.
Initialization
The ISL6432 automatically initializes upon receipt of input
power. Special sequencing of the input supplies is not
necessary. The Power-On Reset (POR) function continually
monitors the input bias supply voltage. The POR monitors
the bias voltage at the VCC pin. The POR function initiates
soft-start operation after the bias supply voltage exceeds its
POR threshold.
Soft-Start
The POR function initiates the soft-start sequence. The
PWM error amplifier reference input is clamped to a level
proportional to the soft-start voltage. As the soft-start voltage
slews up, the PWM comparator generates PHASE pulses of
increasing width that charge the output capacitor(s).
Similarly, all linear regulators’ reference inputs are clamped
to a voltage proportional to the soft-start voltage. The ramp-
up of the internal soft-start function provides a controlled
output voltage rise.
Overcurrent Protection
All outputs are protected against excessive overcurrents.
The PWM controller uses the upper MOSFET’s
on-resistance, r_DS(ON) to monitor the current for protection
against shorted output. All linear controllers monitor their
respective FB pins for undervoltage events to protect against
excessive currents.
A sustained overload (undervoltage on linears or overcurrent
on the PWM) on any output results in an independent
shutdown of the respective output, followed by subsequent
individual re-start attempts performed at an interval equivalent
to 3 soft-start intervals. Figure 1 describes the protection
feature. At time T0, an overcurrent event sensed across the
switching regulator’s upper MOSFET (r_DS(ON) sensing)
triggers a shutdown of the V_OUT1 output. As a result, its
internal soft-start initiates a number of soft-start cycles. After a
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