Measuring Current on NUCLEO-N657X0-Q

[Dresult]

Hi everyone,
I'm trying to measure the current consumption of the MCU/NPU on a NUCLEO-N657X0-Q board. According to the reference manual (https://www.st.com/resource/en/user_manual/um3417-stm32n6-nucleo144-board-mb1940-stmicroelectronics.pdf - see par. 7.4.4), I tried both removing resistor R13 and measuring the current with a multimeter across pins 9-10 on CN12, and removing R40 and measuring across pins 3-4. In the first case, I couldn't measure anything at all, so I assumed the board was in SPMS mode and tried the second option instead. However, when measuring the current across pins 3-4, I got a reading in the order of 40 microamps, which seems implausible. Notably, I'm trying to measuring while AI validation is ongoing in CubeMX.

I'm wondering whether I might have made a mistake with the board, or if the issue lies with the measuring instrument.

Thanks!

[David SIORPAES · Accepted solution]

Hello,

After removing R40, current flows through R41 shunt resistor (50 mOhms). So, with the multimeter you should measure voltage drop on CN12 3-4 pins (not current) and then compute the resulting current: I=Vshunt/50m

Hope this helps,

David

[Dresult]

Thank you very much, I did not know that. I had read the manual (section 7.4.4, second bullet) word by word and was convinced that from those pins I could measure a current.