Oversampled digital controller IC based on successive load-change estimation for dc-dc converters

This paper presents an oversampled digital controller IC for low-power switch-mode power supplies (SMPS) that achieves fast response with a minimized addition of switching losses due to its control actions. To reduce the voltage deviation and improve converter response time, the controller samples the output voltage four times per switching cycle. A single voltage sample is processed by the conventional digital PID compensator to provide tight voltage regulation. Three additional samples are used to calculate the change in duty ratio value that results in the fastest possible response. If the load disturbance is significant, potentially causing large deviation, additional switching pulses are injected based on the estimated load change. To prevent operation at frequencies larger than the switching frequency, while still taking into account the results of oversampling, a novel oversampled digital pulse-width modulator (ODPWM) is introduced. The ODPWM adds or subtracts additional pulses such that the extra pulses are most effective in achieving fast recovery. The controller is implemented on-chip in CMOS 0.18µm technology. The complete controller occupies 0.53 mm² of silicon area and takes only 5500 logic gates for the implementation. Its functionality and effectiveness are demonstrated on a 12-V-to−1.8-V, 60-W buck converter switching at 500 KHz. Compared to a fast PID compensator, having crossover frequency equal to 1/10^th of the switching rate, the new IC reduces the voltage deviation by two times.