Dear team,
My customer uses our 6pcs UCC21732-Q1 in their traction inverter projects. Recently they found a problem, there is oscillation at FLT pin. Below is their schematic, and 6pcs UCC21732-Q1 have the same schematic. The FLT pin of three phase low side driver are connected together. There are two PCB boards in their project, driver board and control board, and there two boards are connected by unshield cable and connector as the third picture.
UCC21732-Q1 is on the driver board. The FLT signal is connected to the CPLD of the control board via the unshield cable, connector and 0.001uF high frequency bypass capacitor（C12789, the second picture）.
When they do the double pulse test, the FLT has oscillation as the forth picture. They tried to change R454 from 3.16k to 1.74k, but the result is still bad. The minimum value is around 0.8-1.2V which is close to the threshold of low signal of CPLD. The test point is TP12840, and they use a twisted cable between test point and test probe.
In order to exclude the effects of the unshield cable and connector, they capture another waveform as the fifth picture, and the test point is C112 which is on the driver board, but the oscillation is still existing. Coul dyou please help analyze the phenomenon? Thanks!
CH1:AL_Vge
CH2:AL_Vce
CH3:AL_Ic
CH4:AL_DESAT_Fault
Thanks & Best Regards,
Sherry
