An Efficient Low-power Dc-dc Buck Converter Chip Design

The fast development of the electronic products and the demand of high-grade power supply always challenge the design of power management chips. The switching power supply is becoming the main power system because of the high reliability, high efficiency, and low dissipation in all power supply types.The characteristics of power management loop controlling methods and modulation modes, the factors inflecting system's efficiency are analyzed and summarized. And then, we mainly discuss the peak current controlling mode and the sub-harmonic oscillation when the duty cycle exceeds 50%. On the base of the theory, we study a kind of high efficiency, low dissipation switching power supply converter. The chip adopts the peak current controlling method; PWM mode and the working frequency are 300 kHz and 500 kHz. When the system begins to start or the output voltage is very low, the system works on 300 kHz. When the system works normal, it works on 500 kHz. The system input voltage range is from 4.75V to 23V and the output voltage rang is from 0.92V to 18V. The maximum output current is up to 2A. Fault condition protection includes cycle-by-cycle current limiting and thermal shutdown. The thermal shutdown temperature range is from -40°C to 165°C. Programmable soft-start minimizes the inrush supply current and the output overshoot at initial startup. The slope compensation circuit is mainly used to restrain the sub-harmonic oscillation. The system also includes voltage regulator, under voltage locked, error amplifier, comparators, band gap voltage reference and gate driver. All of the block are simulated and meet the spec. At last, the layout of the whole chip is shown.The circuit is designed on umc0.35cdmos process and simulated via Spectre of Cadence. The efficiency is up to 93%.