ISL6323A Datasheet, PDF (24/35 Pages) Intersil Corporation – Monolithic Dual PWM Hybrid Controller Powering AMD SVI Split-Plane and PVI Uniplane Processors

ISL6323A
period, it will attempt a soft-start, as shown in Figure 16. If
the fault remains, the trip-retry cycles will continue until
either the fault is cleared or for a total of seven attempts. If
the fault is not cleared on the final attempt, the controller
disables UGATE and LGATE signals for both Core and North
Bridge and latches off requiring a POR of VCC to reset the
ISL6323A.
It is important to note that during soft start, the overcurrent
trip point is increased by a factor of 1.4. If the fault draws
enough current to trip overcurrent during normal run mode, it
may not draw enough current during the soft start ramp
period to trip overcurrent while the output is ramping up. If a
fault of this type is affecting the output, then the regulator will
complete soft start and the trip-retry counter will be reset to
zero. Once the regulator has completed soft start, the
overcurrent trip point will return to it’s nominal setting and an
overcurrent shutdown will be initiated. This will result in a
continuous hiccup mode.
Note that the energy delivered during trip-retry cycling is
much less than during full-load operation, so there is no
thermal hazard.
OUTPUT CURRENT, 50A/DIV
0A
OUTPUT VOLTAGE,
500mV/DIV
0V
3ms/DIV
FIGURE 16. OVERCURRENT BEHAVIOR IN HICCUP MODE
NORTH BRIDGE REGULATOR OVERCURRENT
The overcurrent shutdown sequence for the North Bridge
regulator is identical to the Core regulator with the exception
that it is a single phase regulator and will only disable the
MOSFET drivers for the North Bridge. Once 7 retry attempts
have been executed unsuccessfully, the controller will
disable UGATE and LGATE signals for both Core and North
Bridge and will latch off requiring a POR of VCC to reset the
ISL6323A.
Note that the energy delivered during trip-retry cycling is
much less than during full-load operation, so there is no
thermal hazard.
OVERCURRENT PROTECTION IN POWER SAVINGS
MODE
While in Power Savings Mode, the OCP trip point will be
lower than when running in Normal Mode. Equation 20, with
N = 1, will yield the OCP trip point for the Core regulator
while in Power Savings mode.
If an overcurrent event should occur while the system is in
Power Savings Mode, the ISL6323A will restart in the
Normal state with the PSI_L bit set to 1.
Individual Channel Overcurrent Limiting
The ISL6323A has the ability to limit the current in each
individual channel of the Core regulator without shutting
down the entire regulator. This is accomplished by
continuously comparing the sensed currents of each channel
with a constant 140µA OCL reference current. If a channel’s
individual sensed current exceeds this OCL limit, the UGATE
signal of that channel is immediately forced low, and the
LGATE signal is forced high. This turns off the upper
MOSFET(s), turns on the lower MOSFET(s), and stops the
rise of current in that channel, forcing the current in the
channel to decrease. That channel’s UGATE signal will not
be able to return high until the sensed channel current falls
back below the 140µA reference.
General Design Guide
This design guide is intended to provide a high-level
explanation of the steps necessary to create a multiphase
power converter. It is assumed that the reader is familiar with
many of the basic skills and techniques referenced below. In
addition to this guide, Intersil provides complete reference
designs that include schematics, bills of materials, and example
board layouts for all common microprocessor applications.
Power Stages
The first step in designing a multi-phase converter is to
determine the number of phases. This determination
depends heavily on the cost analysis which in turn depends
on system constraints that differ from one design to the next.
Principally, the designer will be concerned with whether
components can be mounted on both sides of the circuit
board, whether through-hole components are permitted, the
total board space available for power-supply circuitry, and
the maximum amount of load current. Generally speaking,
the most economical solutions are those in which each
phase handles between 25A and 30A. All surface-mount
designs will tend toward the lower end of this current range.
If through-hole MOSFETs and inductors can be used, higher
per-phase currents are possible. In cases where board
space is the limiting constraint, current can be pushed as
high as 40A per phase, but these designs require heat sinks
and forced air to cool the MOSFETs, inductors and
heat-dissipating surfaces.
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