Is there *any* dynamic activity expected in an nRF52 while in SYSTEM_OFF mode ?

[Russ Mirov]

For quite a while I've noticed that across multiple custom boards using the nRF52 I've been seeing low-level current spikes from a part that is in SYSTEM_OFF mode.  They are very narrow, and perhaps 20uA high.  Typically the system power is << 1uA in this mode.   As a sanity check simply replacing the system being monitored by a 10Meg resistor shows the expected (small) current without any dynamic activity.

Over and over I've read that everything is shut down and static in SYSTEM_OFF mode.  What is still active ?

-Russ

[Vidar Berg]

Hi Russ,

Periodic current spikes are expected in System ON and System OFF because of the auto-controlled refresh mode feature in our internal supply circuit. Explanation copied from the Current measurement guide:

"The nRF52 power supply uses auto-controlled refresh modes to maximize efficiency. What this basically means is that a capacitor is recharged regularly to provide power to the chip. The recharge off the capacitor happens during a very short time interval, and results in a high frequency peak in current. This peak is measured to be about 10 - 15 us long. In order to get the correct average current during these peaks, a sampling frequency corresponding to half the peak length is required. This results in a minimum frequency of 200k samples per second (1 sample every 5 us)."

I don't think there is anything active in your case since the measured current is below 1uA. Almost everything is forced off in System OFF. It's only the wakeup source, IO configurations, and RAM retention that should have any impact. 

Regards,

Vidar