[X-NUCLEO-LPM01A] Voltage drops from 3.3V to ~1.5V when powering Arduino UNO for current measurement

[Uday]

Hi STM Community,

I'm trying to use the X-NUCLEO-LPM01A board to measure the current consumption of an Arduino UNO during simple blinking states.

Setup Description:

• Power output is taken from CN14 (OUT and GND pins) on the LPM01A.

• These lines are directly connected to the Arduino UNO's 3.3V pin and GND.

• The LPM01A is powered via USB and in normal measurement mode.

Problem:

• Before connecting Arduino UNO, LPM01A display shows a stable 3.3V (or sometimes 3.27V).

• After connecting the Arduino UNO, the voltage drops to ~1.5V, and the Arduino does not power on.

Working Comparison:

Previously, I tested the same setup using STM32 NUCLEO-C031C6 as the target board.

• I removed SB2 and SB23 bridges as per the reference manual.

• In that setup, everything worked as expected — voltage remained stable, and current measurements were valid.

My Questions:

1. Why does the voltage drop when powering the Arduino UNO?

2. Is it not recommended to supply power directly to the Arduino UNO's 3.3V pin using LPM01A?

Thanks in advance for your help!

[TDK]

It should work fine. What pins are you using? Should be using pins 1 and 3 of CN14. Perhaps show a picture of your setup.

[Uday]

[Uday]

Thank you for the response.

Yes, as specified in the user manual, I’m using pin 1 (GND) and pin 3 (VOUT) of CN14 on the X-NUCLEO-LPM01A board.