A Dual-Mode Buck Converter with Light-Load Efficiency Improvement and Seamless Mode Transition Technique

In order to improve the efficiency over a wide load range, a power converter of the Internet of Things (IoT) usually works in dual modes, which are pulsewidth modulation (PWM) and pulse frequency modulation (PFM). A mixed load detection scheme is adopted to enable the appropriate modes under different loads, whose analog detector has an accurate detection in the heavy load, and the digital load detection improves the light-load efficiency. When the power converter operates in different modes, the control loops are different. Meanwhile, a seamless mode transition technique (SMTT) is presented in this article to improve the transient response during mode change between PWM and PFM. A test chip was fabricated in a 0.18- mu m standard CMOS process, and the chip area is 1.59 x 1.37 mm(2 ). The experimental results show that the efficiency is above 85.3% under V-IN= 3.3 V, V-OUT = 1.8 V, and in the load range from 1 to 300 mA, while peak efficiency can reach 96.1% at 100-mA load. Compared to the case without the proposed technique, the under/overshoot voltage can be reduced by above 55% during the mode transition.