A Transient-Enhanced Constant On-Time Buck Converter with Light-Load Efficiency Optimization

Two key challenges in designing regulators of handheld devices are load transient time and light-load efficiency. A constant on-time (COT) buck converter is often adopted because it facilitates a fast response with reasonable light-load efficiency. For further improvement, two techniques are proposed in this work. One is the transient-enhanced technique which can reduce the settling time and minimize the voltage dips. The other one is the self-tuning technique to improve the light- load efficiency, termed as the near-optimal reverse current calibration (NORCC). The proposed COT buck converter is realized in 0.18-μm CMOS. Measurement results demonstrate settling time and undershoot voltage of 960 ns and 50 mV, respectively, during the load changes from 100 mA to 1.5 A. The efficiency is better than 79% from 10 mA to 1.7 A; the peak value is 93.6% at 300 mA load current.