Fully-integrated DC-DC converter IC for portable devices (in collaboration with MIT)

Abstract

Switch-mode converters prevail in portable devices. By having two operation modes (continuous conduction mode and discontinuous conduction mode), and utilizing energy storing elements such as inductors and capacitors, many DC-DC converters are able to achieve higher conversion efficiency than linear devices. However, conventional DC-DC converter designs include a large inductor which occupies most chip area. Reducing the size of inductor is important to reduce the size of the converter ICs. One way to reduce the inductor is to increase the switching frequency. However, conventional bulk converters efficiency drops significantly when switching efficiency is beyond 1MHz under continuous conduction mode. The switching loss increases since the current in the power switches does not drop to zero during switching.

To solve this problem, this project applies a novel control scheme using boundary conduction mode. The process used in this design is GF130BCDlite. This project designs a hysteretic voltage controller, a hysteretic current controller, a dead-time controller and level shifters. As compared to [1-3], the design features a smaller inductor, wider input and output voltage range, higher load current, smaller load ripple and smaller transient load change. Design from [3] uses smaller inductor but does not support a relatively large load current or good conversion efficiency. [4] features a very small inductor size and relatively high conversion efficiency but the input and output voltage ranges are limited and output voltage ripple is compromised. [5] is a strong design with high conversion efficiency however, it has a large inductor, limited load current and large transient load change.