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I want to measure the current consumption of the uC on my STM32 Nucleo-64 evaluation board (NUCLEO-L073RZ). The manual says, that I just have to remove the JP6/IDD jumper and then connect the pins to an ammeter: enter image description here

But if I just remove the JP6 jumper (no pin connection), the uC is still running (I can still debug/communicate via I2C). I would have expected, that if the JP6 is removed, the uC is no longer powered and therefore not accessible anymore...

Can somebody please explain me, where is my error in reasoning?

Here is the link to the corresponding STM32 Nucleo-64 manual (page 23):

user9564464
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  • did you connect external power? or does it consume parasitical current through communication lines? – Tarick Welling May 29 '19 at 14:13
  • How are your I2C lines are connected / pulled up? – theSealion May 29 '19 at 14:17
  • I am using the default settings of the jumpers (from factory) and currently only removed the JP6/IDD jumper and connected only the mini USB port to my PC (no I2C wires anymore, to exclude external problems). The power supply cames therfore from the USB/integrated ST-Link interface. Strange thing: Even if I remove all external connections except the USB, I still can connect to the uC (with STM32 ST-Link Utility) and program/debug (the debug LED is blinking alternating red/green)... – user9564464 May 29 '19 at 15:01

2 Answers2

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Connecting the USB to the debug port IS powering the MCU through the debug pod. Try removing the 2 ST-LINK jumpers on upper left an inch from the the USB connector. That disconnects the built-in ST-LINK from the MCU. That might remove the power from the debug pod to the MCU.

Richard at ImageCraft
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I found the reason: the problem was my fuse in the multimeter was broken and the irritating LED on the Nucleo is always ON (independently of the MCU is running or not)...

user9564464
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  • The "irritating" LED is indication that the LDO that feeds the LDO connected to your microcontroller is functioning properly and this is a standard debug mechanism for PCBs – bigwillydos Jun 11 '19 at 18:18
  • Yes. I am quite new to that HW topic, but this experience was quite instructive :) – user9564464 Jun 11 '19 at 18:24