High-frequency digital controller for DC-DC converters based on multi-bit Σ-Δ pulse-width modulation

This paper introduces a novel digital controller for low-power dc-dc switching converters that allows operation at very high constant switching frequencies and can be implemented with a simple hardware. The key components of the controller are new digital pulse-width modulator (DPWM), which is based on multi-bit sigma-delta (Sigma-Delta) concept, and a dual-sampling mode PID compensator. Depending on the conditions in the converter circuit, the output voltage is either sampled at a frequency lower than the switching frequency or at the switching rate. The undersampling, which is used in steady-state, minimizes power consumption of the controller. During transients, to achieve fast dynamic response, the controller samples at the switching rate. Operation of the controller is verified with an experimental FPGA system and an integrated circuit (IC), which utilizes the Sigma-Delta DPWM architecture, is designed. Pulse-with modulated signals produced by the new IC at frequency of 115 MHz are obtained and closed loop operation with a 2 W buck dc-dc that switches at 2 MHz is demonstrated.