nRF52840 in System OFF mode

[bojan]

Hello, guys.

I have a few questions for you regarding nRF52840 SoC...

One of our intentions was to measure the current consumption of nRF52840 SoC in System OFF mode using the nRF52840-DK board. For that purpose:

• We have prepared the nRF52840-DK as explained in this guide. 
• We have the SW6 switch set in nRF ONLY position
• PPK II was used as a source meter as illustrated below:

With such a setup, we were able to measure the following:

nRF5 SDK v17.1.0 bare metal samples:

1. Power Management Example as it is: ~4.7uA in System OFF mode.
2. Power Management Example with NRF LOGS and CPU Usage Monitor disabled in sdk_config.h file: ~3.6uA in System OFF mode.

nRF Connect SDK v2.1.0 Zephyr-based samples

1. Sample from samples/boards/nrf/system_off:  ~4.3uA in System OFF mode.

According to what I was able to read so far (e.g. this thread), those periodic current spikes in System OFF mode are expected (LDO regulator in refresh mode) but the current consumption between the refresh mode spikes should be 0.

• Do you have any idea what we are missing here and why we can't have 0uA between two refresh mode current spikes (e.g. something on the nRF52840-DK board where the current is leaking)?
• Is it needed to explicitly enable/disable the internal DC-DC regulator of nRF52840 SoC in order to optimize the current consumption?

Thanks in advance for your time and efforts. Looking forward to reading from you.

Sincerely,
Bojan.

[Stian Røed Hafskjold]

Hi, I think you just need to plug in the USB cable and you should be good. (assuming you connect it exactly like in the picture you posted, which does not have the USB connected)

Here is how I connect the DK:

And here is the idle current measurement, running the beacon sample:

2.2uA

Here is the hex file if you want to check:

3286.nrf52840_xxaa.hex

Best regards,
Stian

[bojan]

Thanks for the explanations, Stian Røed Hafskjold.

After plugging in the USB cable, I was able to measure ~0.85uA in System OFF mode:

I guess this is more or less in accordance with the numbers in a datasheet.

Would you be so kind to briefly explain why it was needed to use 5V power supply from USB in order to get the realistic numbers of current consumption?

Thanks for your support.

Cheers,
Bojan.

[Stian Røed Hafskjold]

Thanks, that is good to hear. The DK has two main power domains, VDD which is powered from the USB, and VDD_nRF (P22) which is powering the nRF chip only.

The reason VDD has to be powered as well is that the analog switch ICs which are isolating the nRF52 from the rest of the circuitry (cutting off SWD lines, etc) is powered from this domain. So if these switches are floating, you can get some leakage current.

Best regards,
Stian

[bojan]

Understood.

Thanks for the additional explanations.

I'm closing this ticket...

Cheers