Design challenges

1. RF, power, sensors and connectors inside the enclosure without degrading any section: 8-layer stackup in 50 × 80 mm.
2. Reliable start-up no matter which charger or cable the user plugs in: USB-C PD negotiation and a dual power path with solar charging.
3. Current spikes without voltage drops: a power stage sized for transients and filtered so noise doesn't spread.