Testing power off current consumption

[nrbrook]

I'm trying to ensure my firmware goes into power off when it should, and that current consumption is as expected when in power off. However, using PPK2 to measure current on the nRF52 DK, I'm having difficulty getting a low power consumption even with an example project.

Is there an example which specifically demonstrates the lowest possible power consumption in power off? If I edit examples/peripheral/template_project/main.c and add NRF_POWER->SYSTEMOFF = 1; at the start of main, the current consumption is between 2.5 and 15ma. What else do I need to add to that example to get to the 0.3uA specified in the data sheet?

[Simonr]

Hi

I discussed this with one of the PPK developers to get a better understanding of what's going on here. First off, the DKs are not optimal to do current consumption measurements on, as the onboard debugger also draws power. ~700uA seems like a leak between the nRF and on-board debugger (OBD). The OBD state when the USB is disconnected is floating, which is not great when you want an exact current consumption. When measuring over the External IN on the DK it will also power (and measure the current draw) of the OBD as well as the nRF chip. 

We recommend using SMU mode, with PPK2 [GND] to DK [External in -] and PPK [VOUT] to DK [nRF_VDD] which is the top pin on SB40 on the DK. That way, you'll power nRF_VDD directly, and bypass everything else. This way you should get the most accurate current consumption of just the nRF52.

Best regards,

Simon

[nrbrook]

Hi Simon, thanks.

I don't think SB40 exists on the nRF52 DK? I tried using [External in -] and VDD_nRF on the shield debug connector, but the result is the same.

Regardless, I fixed the problem with my code on my custom circuit so now I get <3uA on that board and don't really need to test this on the DK.

Thanks