(A) current mode hysteretic buck converter with auto-selectable frequency locking technique

Abstract

A current mode hysteretic buck converter with auto-selectable frequency locking is presented. To reduce difficulty in designing electromagnetic interference (EMI) filter, the switching frequency of the proposed hysteretic converter is locked. The main method of locking switching frequency is to change the resistance appropriately according to switching conditions. In addition, the locked switching frequency is reduced, such as auto-selectable frequency behavior for predictable output harmonics while improving power efficiency at light load. Moreover, the proposed hysteretic converter also adjusts the hysteresis to minimize the range of resistance required to enable frequency locking at light load. The proposed hysteretic converter is implemented in TSMC 65nm CMOS process. The chip area is 900$\mu$mⅹ900$\mu$m. The switching frequency of proposed hysteretic converter fixed at 125kHz, 250kHz, 500kHz, and 1MHz in the specified range of the load current range from 14mA to 500mA. The simulated frequency error relative to the reference frequency is within 1.74% at 3.3V input voltage. Furthermore, the simulated value of the maximum power efficiency is 97.3%.