What really interests me about this design is the ~~buck~~ Boost-converter
So this ~~buck~~ boost-converter is 100% core-independent. The Analog Comparator, TimerD, CCL, and Event-System are all active while the AVR DB sleeps, meaning that the microcontroller can run this simple ~~buck~~ boost-converter without any cost to CPU time.
An incredible design that demonstrates the flexibility of AVR DB's combined peripherals.