Upon testing how a RAK3172 responds to power glitches or cycling and having a 10uf on power plane, I have found that:
- Many times the ENCKEY loses value and becomes 0000000000000000. For P2P operation the other P2P settings seem to endure.
but sometimes an even more serious thing happens…
- The device becomes unresponsive: AT Command response and the loaded program stop.
The firmware must be reloaded via a process to get the device active again…
Using STM32CP Uart mode…Boot Mode…Full Chip Erase… then Load RAK3172_v1.0.4_Boot+App_20220218.hex , then Load RAK3172-E_latest.bin then I can load my custom firmware again…working.
However, changing to a 100uf cap. appears to much lessen the device from becoming unresponsive, but the ENCKEY can still lose setting but also much less frequently.
Also found that keeping Reset low during sustained power cycling prevents the above symptoms. So as long as the Reset pin is kept low during power glitches, I have not seen this issue.
Any ideas to fully protect the device without external brownout circuit?
Is there a way to have longer on-chip reset and brownout delay?