Hi Lawrence,
Common-mode transients greater than 100V/ns can create interference between the input and output circuitry, rendering the output unstable. As an example, take the waveform below, captured using the CMTI setup in the UCC21520 datasheet (Figure 33). Both inputs are held to VCCI, the part is enabled, and the dead time is set to allow output overlap (DT tied to VCCI). With the common-mode transient much larger than 100V/ns, the output state will occasionally falter as seen by the dips in OUTA after about 25ns. Increasing the transient slew rate will eventually cause the output to go low, as though no input signal was being received. This fault clears after the transient condition concludes. The slew rate where issues begin will vary depending on die temperature, supply voltages, variations in the fabrication process, and layout quality.
CH1 (Yellow): OUTA (to VSSA)
CH3 (Purple): OUTB (to VSSB)
CH2 (Blue): Control ground to VSSA/VSSB (common mode transient)
Cursors: Slew rate measurement (192.7V/ns)
Regards,
