Fully Digital Current Mode Constant On-Time Controlled Buck Converter with Output Voltage Offset Cancellation

Fully digital current mode constant on-time (COT) control buck converter with output voltage offset cancellation is presented in this paper. Current mode COT can achieve fast transient response and low output voltage ripple with additional current path. To fully digitalize the control loop in this work, both current mode control and the additional current path are implement in digital way. However, the current path may induce inevitable output voltage offset. To ensure effective output voltage regulation within all load current ranges, an output voltage offset cancellation mechanism was proposed. A prototype converter was fabricated using 0.18 μm CMOS process technology. The controller was fully implemented as a standard-cell-based digital circuit. Measurement results indicated the output voltage regulation in full-load range was 2%, and 100 mV output voltage overshoot under 2.5A load transient response.