A Fixed-frequency hysteretic controlled buck DC-DC converter with improved load regulation

Hysteretic control is widely adopted in the power management units (PMUs) for modern electronic devices due to their simple and stable control architecture, as well as the fast load transient response. However, the switching frequency of a traditional hysteretic converter is not fixed. It changes with operating condition and component aging, and hence brings in electro-magnetic interference (EMI) problems and multiphase interleaving difficulties. In this work, a hysteretic buck converter with frequency-locking capability is presented, where the switching frequency is adjusted by tuning the hysteretic window. In addition, the current-mode hysteretic control in this work utilizes a simple feedback network, which consists of only passive components and yet provides significant improvement on output voltage regulation. To achieve good reliability at high temperature and high voltage, the proposed buck converter has been fabricated in a 1μm SOI process with a chip area of 6mm². Experimental results measured at 1MHz fixed switching frequency with 12V-to-5V voltage conversion and 0.9A load current shows a peak efficiency of 91%.