3.3V external power supply

[lcopparoni]

Hi everyone, I need to power my F401RE with a 3.3V external power source. I read in the datasheet I need to connect the power source to the CN7 pin 12 or CN7 pin 16. Where do I connect GND signal apart from 3.3V signal?

Also, from what I understood, I need to desolder SB2 AND SB12 to get it working, to mantain the ST-LINK functionalities.

Am I correct? Do I need to remove/change any jumper positions? I don't seem to find info about jumpers for 3.3V.

Thank​ you

[CMYL]

Hello,

Do you mean NUCLEO-F401RE (MB1136) ? according to UM1724 (section 6.3.3), When the STM32 Nucleo board is power supplied by +3.3V, the ST-LINK is not powered, thus the programming and debug features are unavailable. When SB2 (3.3V regulator) and SB12 (NRST) are OFF, means that the ST-LINK is also disconnected (even powered by USB).

According to MB1136 page 3, in order to keep ST-Link use USB, VIN (CN6.8 or CN7.24), or E5V, the +5V (CN6 pin 5 or CN7 pin 18) .

Best regards

[lcopparoni]

Hi,

Thanks for the reply.

Yes, you're right, the st link is off when powered with a 3.3V external power source. I don't need the st link, so I'm fine with this anyway.

For​ the other questions could you please help me? Do I need to desolder SB2 AND SB12 to get 3.3V external power source working?

[CMYL]

Hi

According to MB1336 (page 1), we can use the +3.3V as external power supply without de-soldering SB2 and SB12. However, remove any jumper from JP5 and mainly be carful to not feed the board with +5V Pin at the same time when +3v3 is used.

[lcopparoni]

Hi,

Thanks for the reply.

Could​ you please give me the link to this MB1336 file? I can't seem to find it. I downloaded several files from ST website about F401RE but didn't find the one you mentioned.

[CMYL · Accepted solution]

Hi

You're welcome 🙂

In NUCLEO-F401RE go to CAD Resources, then select Schematic Pack or use this link below:

https://www.st.com/resource/en/schematic_pack/nucleo_64pins_sch.zip

BR