abnormal reboot in nRF52832 (urgent)

[Roh]

Hi, guys.

Its developing with nRF52832.

I have a big problem rebooting. could you help me?

to solve this problem, I tried the following : (of course, it is very stable now.)

  > improving inrush current which of peripheral device to protect POR condition (like a 300mV, 300msec)

  > improving Batt. terminal's tension for conducted resistance reduction.

      - coin cell is LR44 and its internal resistance is 1.65 ohm.

      - working voltage 3V(=2 coincell)

The following are the pre-occurrence symptoms : 

  > continuous retry BLE connecting after occur communication disconnecting.

  > voltage drop (like below image)

ref. : Our SDK version is ver15.3 which is including a part of v16.0 and 17.2
        Because our device is a medical device, it is impossible to change the version.

[Roh]

I know well that the waveform in the picture is the POR condition.
So, we improved the inrush current and Batt. terminal tension to get rid of it.
BLE connection interval is a slave latency 3(75~100msec) and AD interval is 230msec before pairing and 750msec after pairing. (in the picture, a small point is AD interval sign which it is at left/right side of deep point..)

our SW engineer worry about next :
-If AD interval is extended, access trying is not available.
-If connection interval is extended, data through put is slow-going.

The idle current is 0.3uA before reset and when reset is occurred, we couldn't catch it since the phenomena had occurred very non-periodically.

[hmolesworth]

Reducing the advertising rate would improve the situation, assuming each of those downward voltage steps is caused by an advertising transmission burst. Perhaps try an extreme case, advertise once per second to see what happens to those voltage steps. If that helps, perhaps there is a compromise advertising rate.

I'm assuming that once connected there is no issue?

[Kenneth]

That was a good suggestion. I was also thinking a bit of the timing here, the duration of that drop is 1.3seconds, which is very close to if you have by accident enabled directed advertisement, when directed advertisement is used, then it will send advertisement packets every 1.25ms for 1.28seconds. This could cause this kind of drop.