Non-obvious power problem

[John]

Hello,

This is less a question and more of a survey. We've recently completed development on a project using the nRF51822 but have run into an odd power problem. We built and tested the first 500 or so units. Our design has the unit in System Off mode while they are in stock or not in use by the customer. However, after a couple of weeks 5 units in stock were found to have completely depleted 2 AAA batteries.

We've gone through all of the usual suspects such as floating pins, misuse of peripherals and most anything we could search for in this forum. So, I thought I would post and see if anyone had experiences with odd power bugs using the nRF51 that they would share to give me additional ideas to try.

We are using the nRF51 as our main processor on this product, and it is running the FreeRTOS port using tickless idle. When we are in our "storage mode" as we call our system off behavior while in stock, the board typically burns well under 1uA. While in stock the units are boxed and the only GPIO that could wake the device back up is a button push which should be impossible.

Thanks in advance for any ideas or just good old war stories.

Regards, John

[John]

Thanks Stefan, I was not aware of that. I'll have the HW guys check on that. For completeness sake, I'll attach the schematic (it's not a complicated board by any means).

Also I wanted to note that this is the first time we have used System Off instead of the System On Idle mode for low power. Additionally it is the first time we have used the sd_power_pof_* API's with the threshold set to 2.1V. I'm not sure if there are any rookie mistakes we could be making with either of those functionalities.