A DC-DC voltage down-converter for an electronic device supplied by a battery and having a bus interface for the interconnection with another electronic device capable of supplying electric power is provided. The DC-DC voltage down-converter includes a terminal coupled to a voltage supply line of the bus interface and operable to receive a input current from the another electronic device. The DC-DC voltage down-converter further includes an electric energy storage element coupled between the battery and the terminal, the electric energy storage element being operable to storage/release electric energy and a drive circuit arranged to control the storage/release of the electric energy storage element, so as to cause an electric power generated by the input current supplied by the another electronic device through the voltage supply line to re-charge the battery. The DC-DC voltage down-converter still further includes a input current feedback control circuit coupled to the terminal and arranged to monitor a value of the input current and generate a corresponding input current indication; the drive circuit configured to control the storage/release of the electric energy storage element according to the input current indication.