I'm currently developing an IoT LoRa node using a Nucleo L432KC. I want the node to be alive more than a year, so I want to test its energy consumption very carefully.

I intended to cut off any unnecessary devices on the Nucleo board, starting with:

  • R22 to cut-off LD2 LED (power supply)
  • D2 to cut-off +3V3_ST_LINK, so the ST-LINK is not supposed to be powered

I power supply the board through Vin (9V).

I did some tests and the whole board is consuming 19 mA when running (idle) and 6 mA in stand-by mode. I don’t understand where those 6 mA are coming from. The STM32L432KC is consuming few uA so it’s not up to the microcontroller (tested with an amperemeter on JP1).

However, the 3V3_ST_LINK voltage which is supposed to be 0V is at 0.85V when the L432 is in sleep mode and 2.65V when it’s running. I don’t know what the origin of this voltage is and I don’t know either where the 6 mA are coming from.

Any idea? :)

Thank you! You can be my hero of the day, maybe of the week!

NB: sch of the board page 29-31 of this doc => http://www.st.com/content/ccc/resource/technical/document/user_manual/e3/0e/88/05/e8/74/43/a0/DM00231744.pdf/files/DM00231744.pdf/jcr:content/translations/en.DM00231744.pdf

  • \$\begingroup\$ Also it might help to check the CubeMX software, even if you don't want to use HAL. It has a energy calculator in it. \$\endgroup\$ – Michel Keijzers Apr 18 '18 at 15:11
  • \$\begingroup\$ The document you've supplied only has 34 pages, so there cannot be a page 56. Try 29-31. \$\endgroup\$ – loudnoises Apr 18 '18 at 17:43
  • \$\begingroup\$ I don't think software is the issue here, as some components are appently powered and they should not... I've used and tried CubeMX software indeed. \$\endgroup\$ – Grany Apr 19 '18 at 8:53
  • \$\begingroup\$ About the document, sorry, my bad! \$\endgroup\$ – Grany Apr 19 '18 at 8:55

SWD lines have internal pullups in the L432 which may put some current into the debugger. Try reconfiguring those pins to to analog with no pullup in your code.

If that does not work - physically cut off the ST-Link part, the board is designed to do that. Later on you can still program the L432 using jumper wires from the 6-pin header on the debugger part.

Also check the quiescent current of any regulators which are used to make 3.3V out of that 9V VIN.

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