Why does the voltage value on the RESET pin of my microprocessor not go high?

Question

I am facing an issue that I do not understand.
I am using a STM32F030K6T6 microcontroller with a capacitor X7R 0603 100nF 10% 50V connected to the ground, whose the value corresponds to the preconization specified in the datasheet as follows:

Most of the time, I do not have any problem. But on really few boards, the microprocessor stays blocked in reset mode because the voltage of the NRESET pin which stays quite low, around 470mV. There is nothing more connected on NRSET signal: only the microprocessor, the SWD connector (without any plugged-connector) and the capacitor.
Do you have any explanation? Could it be because of ESD? A broken capacitor series ? (I have measured its resistance with the ohmmeter to check if there is a short circuit, but it's greater than 1Meg Ohm) Or an issue of capacitor charge/discharge?

Justme · Answer

If you removed capacitor and MCU now works, and since MCU works after adding a new capacitor, the problem was a faulty capacitor.
It could have been damaged at some point during board manufacture or handling, so it might have a had a microscopic crack, and when pressure is applied (by handling the board or thermal expansion) the capacitor might short out or become leaky.

Why does the voltage value on the RESET pin of my microprocessor not go high?

One Answer

Add your own answers!

Ask a Question