ACPL-336J-000E View Datasheet(PDF) - Avago Technologies
Part Name
Description
MFG CO.
ACPL-336J-000E
Avago Technologies
'ACPL-336J-000E' PDF : 18 Pages View PDF
Introduction to DESAT Detection
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 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
IGBTs during a fault condition.
A circuit providing fast local DESAT detection and shutdown is an ideal solution, but the number of required compo-
nents, board space consumed, cost, and complexity have until now limited its use to high performance drives. The
features that this circuit must have are high speed, low cost, low resolution, low power dissipation, and small size. The
ACPL-336J 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 optically isolated fault and UVLO
status feedback signal into a single 16-pin surface mount package.
The fault detection method, which is adopted in the ACPL-336J, 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
circuitry is simply disabled to prevent false ‘fault’ signals.
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 ACPL-336J limits the power dissipation in the
IGBT even with insufficient gate drive voltage. Another more subtle advantage of the desaturation detection method
is that power dissipation in the IGBT is monitored, while the current sense method relies 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.
Output Control
The outputs (VOUT, FAULT and UVLO) of the ACPL-336J are controlled by the combination of VCC1, VCC2(UVLO), LED
current IF and IGBT desaturation condition. The following table shows the logic truth table for these outputs.
VCC1
Low
Low
Low
Low
High
High
High
High
VCC2 (UVLO)
Low
High
High
High
Low
High
High
High
IF
X
Low
High
High
X
High
Low
High
DESAT
Not Active
Not Active
Active (no DESAT fault)
Active (DESAT fault)
Not Actve
Active (DESAT fault)
Not Active
Active (no DESAT fault)
VOUT
Low
Low
High
Low
Low
Low
Low
High
Fault
Low
Low
Low
Low
High
Low
High
High
UVLO
Low
Low
Low
Low
Low
High
High
High
The logic level is defined by the respective threshold of each function pin.
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