A fast transient response DC-DC converter with an active compensation capacitor module

Abstract

An active capacitor module is proposed to be implemented as a dynamic compensation capacitor at the output of the operational transconductance amplifier (OTA) to improve the load transient response of a DC-DC converter. To enhance the response speed during transient event, an active compensation capacitor module (ACM) is adopted to instantly reduce the capacitance of the compensation capacitor. Compared to the traditional approaches by increasing the transconductance gm of the OTA which introduce higher power consumption, the proposed ACM is more power efficient and it also occupies seven times smaller footprint than the large passive compensation capacitor in this work. A current-mode buck DC-DC converter with an ACM is implemented in 0.18 μim CMOS process and simulated across different process corners. Post-layout simulation results show an excellent load regulation of 0.008 mV/mA during load current variations from 50 μA to 1 A in 1 μs, and the proposed converter is working excellently under different load current steps. Output overshoot/undershoot voltages of 15 mV/22.8 mV with 5.9 μs/6 μs recovery time and 29.5 mV/47.5 mV with 8.8 μs/7.2 μs recovery time are obtained under 0.5 A load current step and 1 A load current step respectively from the simulation. Compared with the conventional converter without ACM, the output overshoot/undershoot voltage and recovery time are approximately reduced by twice and five times respectively.