This paper proposes a dual-mode digital-control buck converter, which provides a 100,000X wide load range for internet of things. The controller and mode selector are implemented in digital circuits that consume only 40.5 nA quiescent current. The proposed load detector does not require any extra current sensor. Not only the switching loss but also the quiescent power dissipation is minimized. A low-power dynamic comparator with adjustable offset is proposed to suppress the overshoot in transient responses. The proposed converter is designed in TSMC 350 nm CMOS process. Simulation results show that the converter provides a 3.3V output voltage from a 3.8V to 5V input voltage in a load range of 1 µA to 100 mA. A 94.7% peak efficiency at 20 mA output loading and a figure of merit (FoM) of 0.48 are achieved.