DC-DC converter with improved light load efficiency and transient response

Battery size of portable electronic devices is restricted by compact device form factors. To effectively utilize the relatively limited battery power, highly efficient DC-DC converters are employed. As portable devices remain in stand-by mode most of the time, improving light load efficiency is essential. In this paper, fast transient control method and linearly scaled gate-driving technique are used to improve the transient response and light-load efficiency of dc-dc converter. The transient response of dc-dc converter is closely related to the waiting time of the device to resume normal operation from standby. The fast transient control operates under a voltage controlled Pulse-Width Modulation mode during steady state and saturation mode during transient. Light load efficiency of DC-DC converter depends on frequency dependent losses and gate driving losses. The optimum gate driving voltage can be accurately modeled by a linear function of the load current to minimize frequency dependent loss. This is achieved by maintaining constant switching frequency and output ripple voltage. Simulation results show 5% increase in light-load efficiency with an overall efficiency of 90% and the transient recovery time of a 450 mA step load change to be less than 9μs.