STM32L0 doesn't start on power cycle.

[LMehm]

Hello!

We are using an STM32L0 microcontroller as a power switch.

The device works correctly when the firmware is started from STM32CubeIDE using the Run command.

However, if we switch the power supply off and then back on, the STM32L0 does not boot.

We suspect there may be an issue related to the reset circuit.

Please see the attached schematic. The relevant device is U6.

Could you please advise?

Thank you in advance.

[Andrew Neil]

Presumably, it does start correctly if you just assert NRST ?

Similar issue here: MCU doesn't start after power cycle; Reset works OK

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@LMehm wrote:

We suspect there may be an issue related to the reset circuit.

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So have you looked at the reset signal with an oscilloscope? Does it meet the datasheet requirements.

It's recommended to have a capacitor on NRST - you don't have that:

PS:

In the datasheet:

https://www.st.com/resource/en/datasheet/stm32l010c6.pdf 

[LMehm]

This is the waveform on NRST pin during startup.

[LMehm]

Adding 100nF capacitor didn't help.

[TDK]

Debug the code and see where it's stuck.

NRST circuit and signal looks fine. That is not the issue. The chip is no doubt booted and running something.

[LMehm · Accepted solution]

We forgot to connect BOOT0 pin to ground.

We fixed this using Option bytes and STM32CubeProgrammer.

Now everything works fine.

[Andrew Neil]

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@LMehm wrote:

Now everything works fine.

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Jolly good - so please mark that as the solution.

[Andrew Neil]

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@LMehm wrote:

Now everything works fine.

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Until you find that you need the BOOT0 functionality !