Okay, so I have disappointing news again. After playing it for an hour or so, the same issue arose and I had to pull it out of the case and basically restart the entire build, so I am now “officially” not participating any longer
I don’t know what the issue is at this point, but the PCB really isn’t following good design principles because of the limited size of the board. Everything really needs a third revision. For what it’s worth, here is my issue. It seems like BATFET is getting disconnected from VSYS after plugging in the charger. I removed all USB-C circuitry and simply tried to charge it from a 12V 1A DC power brick, but the same issue is happening which rules out the USB-C being the problem. See below my issues:
Basically what happens is this. As soon as I connect a charger source, sometimes it will charge the cells. Other times it will not charge. It seems to be very random. If it turns out cells don’t charge, then when I disconnect the charger, the batteries get disconnected, and VSYS becomes low until I reconnect the batteries. Basically, the portable can be played with charger connected, but the batteries won’t work at all. The chip does get extremely hot when charging immediately, leading me to believe that it is poor layout. Here are my guesses:
- Charging VBUS cap is not close enough to the IC, with the trace going under a single small via and returning to a small via rather than using big polygons like I should have
- The VSYS output caps for the BQ are not grounded to the IC itself and instead are grounded to the GND plane.
- One small via connecting the GND pins of the BQ to the GND plane. I have thermal vias underneath the GND pad, but I guess this still might not be enough.
Perhaps someone else (Gman/Aurelio) who are more familiar with the BQ25895 can let me know if they do know why BATFET would shut off in this scenario. For now, I am going to read the datasheet back to front and head back to EAGLE to try a third revision.