Power-up problem STM32L4

[Alvar Ollon]

Posted on December 21, 2017 at 13:38

Hello,

Having a problem to startup the STM32L4 MCU. After powering the board it seems like the controller does not start or get stuck. Running with a debugger works fine but when removing the debugger connection and power cycle the board, the controller does not run. I also tested to add an external watchdog and the controller started and behaved as expected. So I started to think that the reset (NRST) pin had to do with the problem. I removed the external watchdog and power cycled the board then I manually reset the MCU by shortly connected the NRST to ground. The MCU started to run as expected.

I would prefer to run without an external watchdog and without a manual reset. I am asking for help to understand why this is happening and how to solve the problem.

[Tesla DeLorean · Accepted solution]

Posted on December 21, 2017 at 13:47

Make sure BOOT0 is pulled low.

[John F.]

Posted on December 22, 2017 at 09:12

Do you have a 100nF capacitor connected from Reset to Vss?

Is your power supply startup ramp monotonic?

[Alvar Ollon]

Posted on December 22, 2017 at 13:26

Hi,

The BOOT0 was not connected so I connected BOOT0 to GND and now the controller works as expected.

Regarding John F’s comment, there is no capacitor between Reset and Vss. It is a capacitor 100nF between Reset and GND. The startup ramp looks fine.

Thank you both for all help!