Overshoot Cancelation Based on Balanced Charge-Discharge Time Condition for Buck Converter in Mobile Applications

Abstract

This paper demonstrates a balanced charge and discharge time condition T=2π√LC=4πRC when R, L and C components are chosen by a relation |Z <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">L</sub> =|Z <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">C</sub> |=2R to cancel the overshoot phenomena in buck converters. This balanced condition is derived based on the state-space technique and the superposition principle. In case |Z <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">L</sub> =|Z <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">C</sub> |<; 2R, the overshoot voltages of this network are improved by a parallel RLC circuit. Furthermore, the ripple voltages are also reduced by the conventional spread spectrum of the pulse width modulation (PWM) method. As a result, a step-down switching power for mobile applications is designed; the overshoot phenomena is improved from 1Vpp into 0.1Vpp, the ripple is kept very small (0.05mVpp), and the electromagnetic interference (EMI) levels are kept below 100μV, which is compared to the desired voltage of 5V.