The UCC21759-Q1 implements a fast overcurrent and short circuit protection feature to protect the IGBT module from catastrophic breakdown during fault. The DESAT pin of the device has a typical 9V threshold with respect to COM, source or emitter of the power semiconductor. When the input is in floating condition, or the output is held in low state, the DESAT pin is pulled down by an internal MOSFET and held in LOW state, which prevents the overcurrent and short circuit fault from false triggering. The internal current source of the DESAT pin is activated only during the driver ON state, which means the overcurrent and short circuit protection feature only works when the power semiconductor is in on state. The internal pulldown MOSFET helps to discharge the voltage of DESAT pin when the power semiconductor is turned off. UCC21759-Q1 features a 200ns internal leading edge blanking time after the OUTH switches to high state. The internal current source is activated to charge the external blanking capacitor after the internal leading edge blanking time. The typical value of the internal current source is 500µA.

Figure 7-5 DESAT Protection