Broadcom ACPL-337J, Reference Manual

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Broadcom ACPL-337J-EB600-RM100
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ACPL-337J Reference Manual Infineon EasyPIM™ 1B IGBT Module EB600-337J Evaluation Board
Figure 10: DESAT Circuitry at ACPL-337J High-Voltage Side
Fault detection implemented in the ACPL-337J monitors the collector-emitter voltage of the IGBT and triggers a local fault
shutdown sequence if the collector-emitter voltage exceeds the predefined threshold. A soft turn-off gate discharge device
slowly reduces the IGBT short circuit current to prevent damaging voltage spikes. Before the dissipated energy can reach
destructive levels, the IGBT is turned off. During the off state of the IGBT, the fault detection circuitry is disabled to prevent
false 'fault' signals. The DESAT fault detection circuitry must remain disabled for a short time period following the turn-on of
the IGBT, to allow the collector voltage to fall below the DESAT threshold. This time period, called the DESAT blanking time,
is controlled by the internal DESAT charge current, the DESAT voltage threshold, and the external DESAT capacitor. The
nominal blanking time is calculated in terms of external capacitance, FAULT threshold voltage (V
DESAT
), and DESAT charge
current (I
CHG
) in addition to an internal DESAT blanking time (t
DESAT(BLANKING)
). Figure 11 shows a diagram describing the
operation of the driver during a DESAT fault condition.
Figure 11: DESAT Protection Sequence. Diagram is the same as in the ACPL-337J data sheet.
The DESAT terminal monitors the voltage between the collector and the emitter (V
CE
) of the IGBT. When this voltage
exceeds 7V, a weak pull-down in the output stage turns on to softly turn off the IGBT. When the gate voltage falls below
V
EE
+ 2V, the Miller clamp turns on to clamp the IGBT gate to V
EE
. After this event, the FAULT output goes low. When
t
DESAT(MUTE)
expires, the LED input needs to be kept low for t
DESAT(RESET)
before the fault condition is cleared. Afterwards,
the FAULT status returns to high. The output stage responds to the input only after the input fault condition has been cleared.
To isolate the collector from the gate driver circuit when the IGBT is off and to be able to adjust the sensed saturation voltage
between the collector and the emitter, DESAT diodes (D2 and D3 in
Figure 10 ) are added in the circuit. By changing the
forward voltage value of the mentioned diodes, the user can modify threshold level of the saturation voltage. This
configuration can be also changed by retaining only one diode and placing a 0Ω resistor in place for the other diode. By
increasing the total forward voltage (the sum of the forward voltages of both diodes), the user can decrease the DESAT
threshold voltage. When using two diodes instead of one, the same type of diodes must be used, and the blocking voltage
rating of these diodes can be half of the maximum reverse voltage. Additionally, the DESAT threshold voltage is adjusted by
adding a low-voltage Zener diode (D1 in
Figure 10 ).