For the 25x driver PCB I decided to control all drivers simultaneously using the CTRL pin of the AL8843. By default all drivers should be off, even if no MCU is actively controlling the board.

To achieve this I'm using an N-MOSFET that is default conducting, pulling all CTRL pins low. If the MCU is connected, it can drive the CTRL_IN pin accordingly. Because the MCU will run at 3.3V, I use a voltage divider to set the gate voltage to 3.3V default.

The finished driver looks like this:

Top: 

Inner1:

Inner2:

Bottom:

The default track width is 0.5mm. With 2oz copper for inner and outer copper layers, this should be enough for conducting the LED currents safely.

For each LED panel with 100 LEDs we plug 2 of these 25x driver boards on either side of the panel. The full lamp is starting to take form: