A smart-USB-cable buck converter with indirect control

This paper presents merits and feasibility of a new DC/DC Buck converter architecture where parasitic inductance available in a USB cable is utilized for energy storage element in an example mobile battery charger application. In this proposed architecture, strategizing the cable as inductor and the converter's active devices at the cable's input side enables inductor heat spread along the cable that has a large surface area. It also allows board size reduction and removes battery charger heat from the load system, e.g. in smart phones, whose stringent thermal limit has been a serious constraint. Since the load and active circuits are on different sides of the cable, the Indirect Control method is proposed to regulate the actual output voltage without directly sensing it as in conventional converters. The Indirect Control is analytically analyzed and verified in simulations and experiments using a 10W smart-USB-cable charger prototype for Li-ion battery application. The converter is switched at 2 MHz for a target voltage conversion from 5V to 3.3V and achieves stable operation across a wide load range and load transients.