- It seems like there is a dip in the VCC_SENSORS when the three voltage regulators are switched on. To check if this is really the root cause, the regulators can be removed one by one. In case all the regulators are removed, and the reset issue still happens, the root cause can be deemed to be different.
- Very narrow spikes on the EXPANDER_RESET can also cause this issue. A n RC filter can be used to eliminate these narrow spikes. The RC can be set to a time constant of around a ball park figure of one fifth the active pulse width on this line. A resistor of 1k is recommended. The C can be selected according to the time constant chosen.
I do not have information about the source of VCC_SENSORS and EXPANDER_RESET. Hence, I am unable to figure out any further causes. Do kindly let me know after you have eliminated the above two root causes.
Thank you for your answer, it was really helpful.
We indeed noticed a dip on VCC_SENSORS which is powering the CYC9520A. It was caused by the voltage regulators which caused a current spike during their activation. The problem is now solved!