The device initiates a soft turn-off when the overcurrent and short circuit protection are triggered. When the overcurrent and short circuit faults occur, the IGBT transits from the active region to the desaturation region very quickly. The channel current is controlled by the gate voltage and decreases softly; thus, the overshoot of the IGBT is limited and prevents the overvoltage breakdown. There is a tradeoff between the overshoot voltage and short circuit energy. The turn-off speed should be slow to limit the overshoot-voltage, but the shutdown time should not be too long that the large energy dissipation can breakdown the device. The 900-mA soft turn-off current of the device ensures the power switches are safely turned off during short circuit events. Figure 7-10 shows the soft turn-off timing diagram.

Figure 8-6 Soft Turn-Off