A reconfigurable high-efficiency DC-DC converter was proposed in order to improve the power efficiency of portable electric devices. A green-mode control strategy was developed to adaptively configure the converter into three modes based on the properties of Li-ion battery in order to achieve seamless step-up/down voltage conversion and minimize power loss. A burst mode control strategy was adopted at light load to reduce switching loss, and the power efficiency was improved. This converter was designed and fabricated in 1.5 μm BCD process, with a total chip area of 8.75 mm2. The input voltage can vary from 2.7 V to 4.2 V, and the output voltage is regulated at 3.3 V. The system can achieve seamless-transition between buck and boost when its input voltage approaches 3.3 V. A zero consumption current-sensing technique based on Gm-C filter was proposed to achieve lossless and accurate current sensing in fast-response current-mode controller. The recovery time for the system was less than 100 μs when its load steps were between 30 mA and 300 mA. The power efficiency of the system can maintain above 80% for 0-500 mA load range, and the peak value can be 94%.