21
Applications Information
Typical Application/
Operation
Introduction to Fault
The HCPL-316J satisfies these
criteria by combining a high
speed, high output current driver,
high voltage optical isolation
between the input and output,
local IGBT desaturation detection
and shut down, and an optically
isolated fault status feedback
signal into a single 16-pin surface
mount package.
on a preset current threshold to
predict the safe limit of
operation. Therefore, an overly-
conservative overcurrent
threshold is not needed to protect
the IGBT.
Detection and Protection
The power stage of a typical three
phase inverter is susceptible to
several types of failures, most of
which are potentially destructive
to the power IGBTs. These failure
modes can be grouped into four
basic categories: phase and/or
rail supply short circuits due to
user misconnect or bad wiring,
control signal failures due to
noise or computational errors,
overload conditions induced by
the load, and component failures
in the gate drive circuitry. Under
any of these fault conditions, the
current through the IGBTs can
increase rapidly, causing
excessive power dissipation and
heating. The IGBTs become
damaged when the current load
approaches the saturation current
of the device, and the collector to
emitter voltage rises above the
saturation voltage level. The
drastically increased power
Recommended Application
Circuit
The HCPL-316J has both
inverting and non-inverting gate
control inputs, an active low reset
input, and an open collector fault
output suitable for wired ‘OR’
applications. The recommended
application circuit shown in
Figure 62 illustrates a typical
gate drive implementation using
the HCPL-316J.
The fault detection method,
which is adopted in the
HCPL-316J, is to monitor the
saturation (collector) voltage of
the IGBT and to trigger a local
fault shutdown sequence if the
collector voltage exceeds a
predetermined threshold. A small
gate discharge device slowly
reduces the high short circuit
IGBT current to prevent
damaging voltage spikes. Before
the dissipated energy can reach
destructive levels, the IGBT is
shut off. During the off state of
the IGBT, the fault detect
The four supply bypass
capacitors (0.1 µF) provide the
large transient currents necessary
during a switching transition.
Because of the transient nature of
the charging currents, a low
current (5 mA) power supply
suffices. The desat diode and 100
pF capacitor are the necessary
external components for the fault
detection circuitry. The gate
resistor (10 Ω) serves to limit
gate charge current and indirectly
control the IGBT collector
circuitry is simply disabled to
prevent false ‘fault’ signals.
dissipation very quickly overheats
the power device and destroys it.
To prevent damage to the drive,
fault protection must be
implemented to reduce or
turn-off the overcurrents during a
fault condition.
The alternative protection
scheme of measuring IGBT
current to prevent desaturation is
effective if the short circuit
capability of the power device is
known, but this method will fail if
the gate drive voltage decreases
enough to only partially turn on
the IGBT. By directly measuring
the collector voltage, the
HCPL-316J limits the power
dissipation in the IGBT even with
insufficient gate drive voltage.
Another more subtle advantage of
the desaturation detection
voltage rise and fall times. The
open collector fault output has a
passive 3.3 kΩ pull-up resistor
and a 330 pF filtering capacitor.
A 47 kΩ pulldown resistor on
A circuit providing fast local fault
detection and shutdown is an
ideal solution, but the number of
required components, board
space consumed, cost, and
complexity have until now limited
its use to high performance
drives. The features which this
circuit must have are high speed,
low cost, low resolution, low
power dissipation, and small size.
V
OUT
provides a more predictable
high level output voltage (V ).
OH
In this application, the IGBT gate
driver will shut down when a fault
is detected and will not resume
switching until the
microcontroller applies a reset
signal.
method is that power dissipation
in the IGBT is monitored, while
the current sense method relies
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