Design and Characterization of Differentially Enhanced Duty Ripple Control for Switching DC-DC Converter

Abstract

This dissertation proposes a new control method, Differentially Enhanced Duty Ripple Control (DE-DRC), for step-down converters in portable applications. With the development of handheld equipment, more power management blocks are required to support multi-functions in a single piece of equipment. The noisy working environment created by different application circuits and also the power supplies themselves, requires the power supplies to be very resistant to the effects of noise. At the same time, the powerful digital computing devices require the power supply to have a fast load transient response in order to achieve high computing efficiency and reliable working support. Because of the large duty ripple voltage with a big noise margin and the low pass filter effect of DDAs, the proposed DE-DRC has good noise immunity. The easily configured positive and negative DDA gains can separately adjust the high and low frequency portion of the loop transfer function, and push the control bandwidth to high frequency in order to achieve fast transient response. Because of a unique first order character of the inner duty ripple loop, this control can also completely eliminate the double pole peaking from output impedance and achieve ideal closed loop output impedance in the control bandwidth, which is preferred for adaptive voltage position designs. These characteristics make this new control method a good candidate for powering next generation digital computing devices in portable applications.

Based on the DE-DRC control method, a monolithic Buck converter is designed and fabricated using TI's LBC7 process. It changes the on-time width according to the input and output voltage to keep the switching frequency relatively constant, and the control part and the power stage are integrated into one chip. The test results show good noise immunity performance and fast load transient response, as predicted.