In this paper, a simple, fully digital, asynchronous finite state machine controller for buck-boost power converters is introduced and simulated. With the addition of only two analog voltage comparators and six power MOS switches, the circuit can generate an output voltage that is able to track a dynamic reference with a 1 MHz bandwidth with good efficiency using a 0.35 mu m CMOS process. The controller also provides adiabatic charging and discharging of capacitive loads.