Using HSE on NUCLEO-L432KC when powered by external +5V

[WQ]

Hi there:

We are going to use NUCLEO-L432KC. The MCU is STM32L432KCU6U. Its main clock HSE is the MCO output of the ST_Link MCU. The NUCLEO-32 PCB has quite a few power options. We are going to use the external +5V mode (+5V on CN4 Pin 4). However, the 3.3V to ST_LINK is not powered by this +5V according to the schematic, and there is no MCO clock because the ST_LINK MCU is not working if external +5V only. So, the MCU can't be HSE clocked when using +5V. Am I reading these correctly? Thanks for help.

-WQ

[Peter BENSCH · Accepted solution]

The behaviour of the included ST-LINK depends on where you feed in the 5V. There are two possibilities: CN4.4 (+5V) or CN1.1 (USB port, VBUS).

If you use CN4.4, the ST-LINK is indeed not supplied, therefore it cannot deliver an MCO signal and you would have to work with the internal clock sources of the STM32L432 (see table 5 of UM1956).

As a way out, you could feed the 5V to CN1.1 or e.g. to the anode of D1, which would supply the ST-LINK again.

In this context, please remember that the NUCLEO boards are only permitted for development purposes and not for end products, as can also be read in the Terms of Use.

Does it answer your question?

Regards

/Peter

[WQ]

Thanks for the reply and the really good suggestion (jumping to D1 anode).

-WQ