The boards with lithium polymer charging are back and I've got mixed news: they mostly work. I ordered two (sponsored) designs from PCBWay: a dedicated lipo charger and a eReader carrier board with integrated lipo charging.

Note how the SD card connector is properly orientated this revision, but is erroneously labeled "v0.4" instead of "v0.5".

The dedicated charger board works exactly as expected. I plug in a USB C cable and it outputs 5V and chargers a lipo battery if it's connected. If a battery is not connected, the board still outputs 5V. The eReader carrier board will charge a lipo battery if it's connected, however, it does not output 5V no matter what. Probing the board revealed that power from the USB micro connector was reaching the BQ24075 battery charger. That chip was even outputting power to the TPS63701 5V regulator. But the regulator didn't output anything. I reexamined the schematics for the dedicated lipo charger and eReader carrier board to eventually discover the problem.

Below is the schematic for the TPS63701 in the fully functional lipo charging board.

Below is the TPS63701 schematic for the faulty eReader carrier board.

For some reason, I grounded the enable pin (EN, pin 14) of the TPS63701 boost converter on the eReader carrier board but not the dedicated lipo charger. I couldn't tell you want was going through my head when I did that. I was able to emulate the same faulty 5V output behavior on the functional dedicated lipo charger by grounding that board's enable pin.

I considered trying to cut traces of the TPS63701's EN pin, but I simply don't have the tools to make modifications that small. Even if I did, the time and energy required to so would probably be best spent working on the long list of firmware I need to write and revving the layout to incorporate the new touchscreens that came in.

Unfortunately, the carrier boards are bricks. The first completely unusable hardware of this project. It took 5 revisions before it happened, so I consider that an accomplishment.

I've progressed in the bring up of GDEY042T81-FT02 enough to do a 6th hardware revision. And boy oh boy, was driving that touchscreen much more convoluted than it needed to be. But that's a project log for a different day.

For the latest status updates please visit the project's Gitlab repository.