How to power NUCLEO-F303K8 or NUCLEO-L432KC with an external supply voltage of +5V?

[VNava.1]

Hi ST community!

My name is Vincenzo I would like to supply my NUCLEO-F303K8 with an external supply Voltage of +5V.

I prepared a Test Project which control the LED3 to blink with a certain frequency. When I supply the NUCLEO through the VIN pin or through USB connector I see the LED3 blinks, but when I provide +5V through the 5V pin I cannot see the LED3 blinks.

What am I doing wrong?

I read the UserManual UM1956 and I cannot understand the reason why I cannot see the LED3 blinks. In this UM I read this procedure:

VIN or +5 V power supply

When powered from VIN or +5 V, it is still possible to use ST-LINK for communication for programming or debugging only, but it is mandatory to power the board first, using VIN or +5 V, then to connect the USB cable to the PC. By this way the enumeration will succeed anyway, thanks to the external power source.

The following power sequence procedure must be respected:

1. Check that SB1 is off

2. Connect the external power source to VIN or +5 V

3. Power on the external power supply 7 V< VIN < 12 V to VIN, or 5 V for +5 V

4. Check red LED LD2 is turned on

5. Connect the PC to USB connector CN1

I don't need to communicate with the PC, for this reason I don't to follow the fifth step.

Also consluting the Electrical Schematic I can see that effectively I provide VDD to the MCU also if I supply the board with +5V pin.

 

Can you help me?

Vincenzo

[KnarfB]

Same situation as here: https://community.st.com/s/question/0D50X00009Xkfm1/stm32l432-nucleo32-external-power

hth

KnarfB

[VNava.1]

Thanks!

[Piranha · Accepted solution]

Unpowered ST-LINK pulls down NRST of the connected slave MCU through pin protection diodes. Either power the ST-LINK or disconnect SB9.

[VNava.1]

Thanks Pirnha, I found confirmation of your solution in the UM 1956 as show in the figure below, but, at the same time, again in the UM 1956, there is a table which says that the SB9 should be removed only in +3v3 supply voltage case.

Do you think it's just an oversight?

Thanks again for your valuable suggestion!

[FFUMI.1]

Hi - has there been had any further development on this?

Requirements are quite straightforward, I think: use external power when USB is not used, still make the internal ST-Link usable when USB is connected.

So, I wonder if a permanent - and efficient - external power solution is ever possible, straight out of the box, or if some external circuitry is needed. If so, does any source or reference exist?

Does ST have something to suggest, about this?