A Digitally Controlled DC-DC Converter Module with a Segmented Output Stage for Optimized Efficiency

This paper presents a 4 MHz, 0.9 W digitally controlled DC-DC converter with a miniature inductor for 1.8 V portable devices. In applications such as cellular phones, it is crucial to achieve high conversion efficiency over the entire load range. A binary-weighted segmented power stage is used to dynamically optimize the converter efficiency by reducing the gate-drive losses at mid-to-light loads. An all-digital segment controller based on a load current estimator is demonstrated. This approach is most effective in the mid-load range, where the losses are reduced by 33%, corresponding to an efficiency improvement of 7.5 % at Vin= 4.2 V. A peak efficiency of 89 % is achieved at fs = 4 MHz and Vin = 2.7 V.