Fully integrated ultra-low-power asynchronously driven step-down DC-DC converter

This paper proposes a fully integrated asynchronous step-down switched capacitor DC-DC conversion structure. The circuit uses a fully digital asynchronous state machine as the heart of the control circuitry. To minimize the switching losses, the asynchronous controller scales the switching frequency of the converter according to the load. It also turns on additional parallel switches when needed. This circuit regulates load voltages from 300 mV to 1.1 V derived from a 1.2 V input voltage. A total of 350 pF on chip capacitance was implemented to support a maximum of 250 μW load power, while providing efficiencies up to 80%. The circuit validating the proposed concepts was implemented in 0.13 μm CMOS technology.