Proposes a digital controller for adaptive power-supply regulation that uses sliding control, which is a widely used technique in switching power supplies for its fast transient response and robust stability. A novel reformulation of the sliding control law enables a simple and power-efficient digital implementation. The reference circuit can be either a delay line or a ring oscillator, and the sensor circuits for both cases are discussed. The prototype chip fabricated in 0.25-/spl mu/m CMOS technology demonstrates a power efficiency of 89% - 95 % over the regulated voltage range of 1.1 - 2.3 V.