nRF52840 reset failure

Question

A problem is experienced with our nRF52840 device, which occasionally stops working and cannot be reset. 
 Below are the issues observed:

The main software is stopped.

A stable power of 3.3V is being supplied.

Tests have been conducted with nRFConnect-SDK v2.6.1 and v2.4.2, with no resolution.

The P0.18 is configured as the nRESET pin.

The device is not reset by pulling down and up of the nRESET pin.

Connections cannot be established using J-Link Segger tools.

The issue is temporarily resolved by disconnecting and reconnecting the battery.

We have noticed the issue mentioned below, where different SDKs were used, but this did not provide a solution. 
 nRF52840 power-on reset failure - Nordic Q&A - Nordic DevZone - Nordic DevZone (nordicsemi.com)

Yang22 · Answer

Hi Simon, 
 
 Thank you very much for your feedback and the solution you provided. 
 The issue occurs when our battery&rsquo;s voltage becomes unstable, fluctuating between 3 V and 0 V in a short time frame, and the reset pin is pulled up by a 3.3V regulator from the battery. We are wondering if the unstable VCC affects the reset pins during these rapid level changes. 
 Reproducing the issue is challenging and can only be reproduced one or two times during a 1-hour test. In our tests, we use a power supply to simulate the battery and incrementally switch the power between 0 V and 3 V. The nRF then powers off and will reboot once the voltage recovers to more than 1.8 V. 
 Thank you for reviewing the hardware of our board. I will create a private DevZone case and upload the relevant files. 
 
 Thanks a lot and Best regards, 
 Yang

nRF52840 reset failure

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