A 600 mA, constant on-time controlled DC-DC converter with 67% conversion efficiency at an output current of 23 μA

This paper describes a constant on-time controlled DC-DC converter that realizes both high efficiency under light loads and fast load transient response. To realize low-power operation, a combination of a simple common-source amplifier and a low-power differential amplifier is used instead of a differential comparator. Using a common-source amplifier cuts power consumption in half compared with using a conventional differential comparator. The power consumption of the differential amplifier is negligible because it determines the DC operating point only. The differential amplifier also improves the accuracy of the DC output voltage. In addition, background calibration by a zero-cross comparator is proposed; calibration guarantees correct discontinuous-conduction mode operation and minimizes power loss at switching. Experimental results for a 600 mA, 3.6 V to 1.2 V DC-DC converter are described. The measured efficiency is 67% at an output current of 23 μA, and more than 80% for output current over 100 μA to 600 mA. Also, a small voltage disturbance of 30 mV is attained at a load-current transient of 590 mA.