High Frequency Buck Converter Design Using Time-Based Control Techniques

Abstract

Time-based control techniques for the design of high switching frequency buck converters are presented. Using time as the processing variable, the proposed controller operates with CMOS-level digital-like signals but without adding any quantization error. A ring oscillator is used as an integrator in place of conventional opamp-RC or G m-C integrators while a delay line is used to perform voltage to time conversion and to sum time signals. A simple flip-flop generates pulse-width modulated signal from the time-based output of the controller. Hence time-based control eliminates the need for wide bandwidth error amplifier, pulse-width modulator (PWM) in analog controllers or high resolution analog-to-digital converter (ADC) and digital PWM in digital controllers. As a result, it can be implemented in small area and with minimal power. Fabricated in a 180 nm CMOS process, the prototype buck converter occupies an active area of 0.24 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> , of which the controller occupies only 0.0375 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> . It operates over a wide range of switching frequencies (10-25 MHz) and regulates output to any desired voltage in the range of 0.6 V to 1.5 V with 1.8 V input voltage. With a 500 mA step in the load current, the settling time is less than 3.5 μs and the measured reference tracking bandwidth is about 1 MHz. Better than 94% peak efficiency is achieved while consuming a quiescent current of only 2 μA/MHz.