System OFF Current in 52840

[michael a]

Good morning,

I am trying to get the lowest current during system OFF (no RAM retention, no wake-up sources configuration) on 52840 PDK. The spec says that the OFF current can be as low as 0.4 uA. However, I cannot get below 1.3 uA. Using the PPK I can see ~40 uA periodic spikes every ~50-60 ms. When I looked through the previously posted questions I concluded that this may be the LDO/DCDC refresh mode, but I am not sure. Could you please confirm?

And if this is really the case, does this mean that there is no way of reaching the 0.4 uA that is stated in the spec?

I used the following code:

int main(void){

    NRF_POWER->SYSTEMOFF =1;

    while(true){__WFE();}

}

Thank you,

Michael

[Håkon Alseth]

Hi,

 

The spikes are due to the regulator refresh mode.

When using the PPK and measuring system off, you are entering the lower end of the resolution for the kit:

It measures current from 1 μA up to 70 mA and gives a detailed picture of the current profile for the user application.

Since you are measuring on a DK, then I suspect this added ~1 uA comes from leakage of external hardware on this board, as there are connections from the nRF to for instance the SEGGER IC, as explained in the note of the DK documentation. Powering the DK from USB will also provide a lot of noise when measuring current, so we recommend that you use a battery.

 

Kind regards,

Håkon

 

[michael a]

Thank you for your answer.

But I think that the added average current is dominated by the refresh mode spikes, not by the PPK resolution nor the USB noise.

Is the refresh-spikes current taken into account in the current consumption numbers you report in the documentation (e.g. the system-OFF 0.4 uA)?

Best regards,

Michael

[Håkon Alseth]

Hi,

 

Our tests are performed with the refresh mode spikes included.

The consumption between each refresh mode spike shall be 0, as the chip is not drawing any current at that point.

 

Best regards,

Håkon