Power consumption measured in IDD

vik_modam · ‎2024-04-11

Im testing the power consumption in my Nucleo-l412kb board while running and stop2 mode.

I found huge discrepancies when I measure current in the IDD pins, powered from the USB host, respect to powering the board with an external power supply and measuring the current in series to the power supply.

Running on HSI at 16MHz, with 9 GPIOs outputs set high and 7 GPIOs in input mode pulled down, and a uart communication, gives me 2.3 mA power consumption, as measured in the IDD pins on board. When entering STOP2 mode I get 0.3 mA (probably I need to reconfigure the GPIOs before entering STOP2 in order to minimize power).

But, with an external power supply at 7V on Vin, I get around 60 mA power consumption, with no change at all entering in STOP2 mode.

What is making such a huge difference? I suspect that the IDD is giving the net power consumption, without the power LED (red), and the st-link, but couldnt find any documentation. Is it also something related to Voltage regulators?

If I would like to profit from the low power I see in the IDD pins, could I power the board through the 3V3 pin and expect that power consumption?

Also, in order to power the board with the 3V3 pin, the documentation says I need to remove the SB14 and SB9 bridges. The SB9 is used for the NRST, so another question is. Would I be still able to program my board If I remove the solder bridges?

Andrew Neil · ‎2024-04-11

@vik_modam wrote:
with an external power supply at 7V on Vin, I get around 60 mA power consumption, with no change at all entering in STOP2 mode.

Is that still measuring through the IDD link, or is that measured at your 7V power supply?

@vik_modam wrote:
Also, in order to power the board with the 3V3 pin, the documentation says I need to remove the SB14 and SB9 bridges. The SB9 is used for the NRST, so another question is. Would I be still able to program my board If I remove the solder bridges?

In general, only the 2 SWD wires are required for programming.

But there are some cases where the hardware NRST line can get you out of a "stuck" state where the SWD lines don't work - so it's always worth having.

If you've broken the NRST link on the PCB, you can always reconnect it using a jumper wire.

vik_modam · ‎2024-04-11

Hi Andrew, the 60 mA I measure at the power supply.

Andrew Neil · ‎2024-04-11

@vik_modam wrote:
Hi Andrew, the 60 mA I measure at the power supply.

Then that will be powering more than just the target processor.

You must measure at the IDD jumper to see only the target processor's consumption!

vik_modam · ‎2024-04-12

What if I am concerned about the total power consumption, not only the processor? I'm planning to use that board for my product. My question is how could I power the board such the total consumption get closer to that of the MCU itself. Do you think powering the board from the +3V3 line could help?

Andrew Neil · ‎2024-04-12

@vik_modam wrote:
What if I am concerned about the total power consumption, not only the processor?

Then you'll have to ensure that your "extras" are powered through the IDD link.

The purpose of the IDD link is to measure the target processor current without including the ST-Link, etc.

You could break-off the ST-Link part:

https://community.st.com/t5/stm32-mcus-products/3-3v-power-supply-for-nucleof103/m-p/657820/highlight/true#M240022

https://community.st.com/t5/stm32-mcus-products/3-3v-power-supply-for-nucleof103/m-p/657826/highlight/true#M240024

@vik_modam wrote:
I'm planning to use that board for my product.

It's a development board - it is not intended for inclusion in a product!

ST's Ts & Cs specifically forbid that.