A 4-Phase Adaptive On-Time Controlled Buck Converter With Auto-Synchronized Dynamic Frequency and Transient-Enhancement Techniques

This article presents a four-phase adaptive on-time (AOT) controlled buck converter with an ultra-fast load-transient response. A dynamic-frequency clock generator is proposed to generate and auto-synchronize three duty signals with 90°, 180°, and 270° phase shifts based on an already-generated duty signal. Interleaving angles between phases are always kept constant even when the switching frequency varies. Unlike the traditional pulse distribution scheme in constant on-time (COT) multiphase buck converters, the generated pulses no longer need to be sequentially distributed to different phases, but synchronized to one phase instead. Therefore, a much faster load-transient response can be achieved. A transient-enhancement scheme is also proposed to remove the speed limitations introduced by the error amplifier (EA) during load transient. The fast response merits of the AOT controller can thereby be fully taken advantage of while a relatively constant operating frequency is maintained under different input and load conditions. Simulated in a 180-nm BCD process, the proposed converter shows a fast load-transient response with 102-mV output voltage droop and 754-ns settling time for a 6A/1ns rapid load current step, where a 22-μF decoupling capacitor with a relatively large equivalent series resistance (ESR) of 15 mΩ is used. Besides, this work achieves a peak efficiency of 89.7% for 5V-to-1.4V conversion, while the efficiency is maintained at >75% over a wide load range from 1 A to 10 A.