High Frequency, High Current Step-down Dc Converter In The Research And Design

In today’s consumer market, portable battery-operated devices, such as smart-phones, tablet PCs, personal digital assistants etc., are playing more and more important role in people’s life. As a result, a high efficiency buck converter as a power management unit has already become an indispensable block for the whole system to extend its run time. Driven by the miniaturization and low cost, the switching power converters are advancing into high frequency to further shrink the volumes of external passive devices such as inductors and capacitors. On the other hand, the increasing complexity and integration of the system require a larger current capability of the converter to support more modules at the same time. So, high frequency, large current are the current trends for high efficiency buck converters. Focused on the high frequency control mode and transition efficiency, a high efficiency buck DC-DC converter with switching frequency of10MHz and maximum load current of1500mA is presented in this thesis. The On-time Control Mode is chosen to control this high frequency converter after compared with all other sorts of control modes. A Self-adaptive On-time Generator (SAOTG) and a Dual Ripple Compensation (DRC) are proposed to solve the inherent problems of frequency variation and system instability for On-time Control Mode, respectively. Besides, with major parts of power loss in buck DC-DC converter revealed, a Self-adaptive Power Transistors Sizing (SPTS) technique is proposed to optimize the overall efficiency. At the same time, SOT/PFM dual modes control and automatic mode transition are used to help improve the efficiency in light load condition.The Self-adaptive On-time (SOT) Controlled buck DC-DC converter is designed and implemented on Chartered2P4M0.35μm CMOS process in this thesis, it can run with small external inductor of0.47μH and capacitor of4.7μF. The measurement results show that the converter works properly in SOT mode, whose frequency is locked in10MHz accurately and output ripple is as small as10mV in steady state. The converter exhibits fast load transient, line transient and DVS response. With the efficiency optimization schemes, the peak efficiency of converter can reach90.16%, and the overall efficiency keeps over80%.