In the applications of traction inverter or motor drive, the power semiconductors are in hard switching mode. With the strong drive strength of UCC21759-Q1, the dV/dt can be high, especially for SiC MOSFET. Noise can not only be coupled to the gate voltage due to the parasitic inductance, but also to the input side as the non-ideal PCB layout and coupled capacitance.

UCC21759-Q1 features a 40ns internal deglitch filter to IN+, IN- and RST/EN pin. Any signal less than 40ns can be filtered out from the input pins. For noisy systems, external low pass filter can be added externally to the input pins. Adding low pass filters to IN+, IN- and RST/EN pins can effectively increase the noise immunity and increase the signal integrity. When not in use, the IN+, IN- and RST/EN pins should not be floating. IN- should be tied to GND if only IN+ is used for non-inverting input to output configuration. The purpose of the low pass filter is to filter out the high frequency noise generated by the layout parasitics. While choosing the low pass filter resistors and capacitors, both the noise immunity effect and delay time should be considered according to the system requirements.