A Current-Mode DC–DC Buck Converter With Accurate Current Limit Using Multiplex PWM Comparator

Abstract

In a conventional current-mode dc–dc buck converter, two sensed inductor current signals are processed in three separate comparators to regulate the converter under various load conditions. These independent sensing currents and comparators not only consume large quiescent current and silicon areas but also cannot guarantee the accuracy of the current limit threshold. This article proposes a current-mode dc–dc buck converter with an accurate current limit using a multiplex pulsewidth modulation (PWM) comparator. Through a multiplex PWM comparator, only one sensing current and one comparator are required to process the inductor current information and complete the regulation of the converter under various load conditions. The response speed of overcurrent protection is also increased without consuming more power and silicon area. Moreover, by generating the zero temperature coefficient (ZTC) sensing current and adding ZTC reference current with slope compensation information, the accuracy of the current limit threshold is greatly improved under various temperatures in a wide input voltage range. The proposed buck converter with a multiplex PWM comparator was fabricated using a standard 1P3M 0.18 <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">μ</i> m BCD (BiCMOS/DMOS) process and the experimental results show that the proposed scheme functions properly in the 5-A load range, and the current limit threshold also varies only 8.1% in the temperature range from −40 to 125 °C with the input voltage up to 60 V.