Correct power supply for Boron 2G/3G without LiPo battery

[nils]

@BDub

You can look back through the Device Diagnostics history at the ‘AT’ column to figure out what rAT it was on. Maybe though in your case if it was connected it will show a 3G RAT, vs. if it was on 2G maybe it wasn’t connecting at all, or just briefly.

The device.network.signal.at column has the value 4 most of the time, a small number of entries has 2. Looking at Restrict Boron 2G or 3G connections - #2 by picsil, 4 can be 2G or 3G if I understand correctly.

@BDub

That’s good to know and we will look into the reason for this.

Thank you. On a 2G/3G Boron without battery and 500mA input current limit the VSYS voltage can drop to ~3V, causing the modem to become unresponsive without influencing the nrf52840. As a consequence, the DeviceOS restarts the modem. This happens rarely, about one to ten times a day. I could reproduce this reliable by drawing a current peak on VSYS. Setting a higher input current limit solves this. I chosed 3000mA, probably a lower limit is ok though.

Look here for a detailed description (I discovered this because of a bug):

Memory leak in Gen3 network handling

As I discovered later, the reason for triggering the memory leak bug was a hardware issue. I describe it here to help people in the future having the same problem: I was powering the boron via the VUSB pin with a powerful (3A) supply (always stable 5V here, ensured with scope), but I didn’t increase the PMIC input current limit. The default is 500mA which is not enough for the Boron 2G/3Gs current peaks. More details: Correct power supply for Boron 2G/3G without LiPo battery This lead to volta…