Hi all,
My customer has a urgent issue on CMPSS of F280039. They are using CMPSS to do over current protection on their inverter project. However, CMPSS is triggered incorrectly. Below are the waveforms:
Channel 6 (orange) is the inverter AC output current
Channel 8 (purple) is the feedback of output current measured at the ADC pin.
Channel 2 (green) is the output of CMPSS.
Channel 7 is VDD.
(The lower half is a Zoom-in of the upper half).
The first three cycles are normal, CMPSS output is high when the current reaches a threshold. In the fourth cycle, CMPSS is triggered at lower current. Since the fifth cycle, CMPSS is always triggered. The behavior looks like CMPSS threshold is decreasing, but we've confirmed DACHVAL is constant by logging it in each cycle.
Also, this problem occurs only when the power stage is on. If we turn off the power stage and feed the current ADC pin with fake sinusoidal current signal. the CMPSS works normally.
We‘ve measured the VDDs, and they are as clean as channel 7.
Any idea what might be the cause?
Thanks,
Hang.
