nRF52832 occasionally doesn't start up with coin cell battery

[Francesco_M]

Dear,

we have some problems at the startup for our nRF52832 board powered with coin cell battery. The hardware include nRF52832 SoC, an accelerometer (LIS3DHTR) and battery holder for CR2032. We have also an additional 10uF capacitor in parallel with battery (in addition to 4.7uF on VDD, pin 48); the battery voltage is connected directly on VDD pins (pin 48, 36, 13). We verifiead that occasionally when we put battery inside battery holder the nRF52832 doesn't start up and seems to go in a state where it draw current that discharge battery in very short time (2 days). When the nRF52832 is in this unknown state the VDD voltage is 3V (the coin cell battery voltage) but there isn't activity on TX and RX and nRF52832 is stucked (if startup procedure is finished normally, nRF52832 will execute firmware instruction normally and therefore it will go on TX/RX periodically). We verified also that when we insert the coin cell battery inside battery holder some bounce on VDD supply voltage occurred. Basing on internal coin cell resistance and capacitor of about 15uF (10uF+4.7uF) the rise time of our "power supply" from 0 to 1.7V should be in the range 10usec.-10msec. and therefore tpor,10msec=9msec. What happen if during tpor time (9msec. in our case) after 1.7V, VDD voltage drop under 1.7V due to contact-non contact from battery with battery holder? What could be the cause of the incorrect startup of the nRF52832 SoC?

Best Regards

[Vidar Berg]

Hi,

If possible, please attach a debugger to the device after it has failed to boot, then call "nrfjprog --readregs," then post the result here. The rise time you outlined should not be a problem. 

Thanks, 

Vidar

[Francesco_M]

Hi Vidar,

many thanks for your answer. It is not simple for us to reproduce the failed boot on nRF52832 because this happen tipical on 2-3 boards every 100, therefore to follow your suggested procedure attaching a debugger to a board we will require time. We will try to reproduce the problem on boot but we noted that it depends how we introduce coin battery inside battery holder. In the meanwhile, please can you give us some hypothesis for the specified boot problem? Many thanks in advance.  

[Vidar Berg]

Hi,

Francesco_M said:

many thanks for your answer. It is not simple for us to reproduce the failed boot on nRF52832 because this happen tipical on 2-3 boards every 100, therefore to follow your suggested procedure attaching a debugger to a board we will require time

Understand that it's difficult to reproduce. Considering that the battery becomes drained within a couple of days I think it's fair to assume that the device stays in this bad state. So when you reproduce this, try not to reset the device. 

Francesco_M said:

In the meanwhile, please can you give us some hypothesis for the specified boot problem? Many thanks in advance.

 It's hard to say. But I think it could be caused by FW. I.e., the power-up sequence of the chip+external sensor causes an assert or hardfault that makes the app hang. Or have you enabled the watchdog timer which should prevent this?