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.

[Kenneth]

It looks to me as the drop is up to 1V and the duration is up to 1.3seconds:

This kind of drop in voltage will unfortunately trigger the POR when voltage return to normal ~3V. To avoid this you will need to either reduce the drop and/or reduce the duration of the drop. What is the connection and advertisement interval here? What is drawing all the current during the 1.3second period? Maybe you can look into increase the connection interval and advertisement interval here?

[Roh]

A capacitor of 100uF is installed in the circuit.
If it's an neighbor cause of MCU, the shotky diode will work, but if it's an MCU itself cause, the diode won't help.
Most of the gpio for external device control is pull up or down with 1M or 10K ohms resister.
For reference, there was no action on the peripheral circuit when the symptoms occurred.