A Fast Fixed-Frequency Adaptive-On-Time Boost Converter With Light Load Ef ficiency Enhancement and Predictable

Abstract

An integrated fixed-frequency adaptive-on-time (AOT) DC-DC converter with fast transient response and enhanced high light-load ef ficiency is presented. At both Con- tinuous-Conduction-Mode (CCM) and Discontinuous-Conduc- tion-Mode (DCM) operation, the on-time is adaptively controlled by a frequency locked loop so that th e switching frequency tracks the reference frequency with less than 0.5% error in the whole operating range. At CCM operation, the reference frequency is fixed at 1 MHz. At light load with DCM operation, the reference frequency hops between 1 MHz and 1 MHz/N where and 1 to 5 according to the loads without load current sensor. Frequency hopping is introduced to boost the ef ficiency as well as reduce the EMI noise problem. A glitch-free on-time control circuit is introduced to increase the track accuracy and speed of the frequency locked loop. A mode decision circuit with digital hysteretic window is used to ensure a smooth transition between CCM and DCM operation. An on-time generator with proper logics is used to suppress frequency bouncing during frequenc y hopping. A prototype with 1.8 V–3.2 V input voltage, 3.0 V–4.2 V output voltage and 0 mA–800 mA load current range has been fabricated in a 0.35 m 2P4M CMOS process. Load transient measurements verify that 8 s–20 s recovery time is achieved for load current increase. Measurement results also show a maximum efficiency of 94.8% is achieved at total output power of 3.2 69 W, and the light load efficiency is enha