EMI-induced failures in PWM controllers for SMPS

Abstract: this paper describes the last achievements on the susceptibility to RF interference (RFI) of smart power system on chip. To this purpose, a PWM voltage-mode switching mode power supply (SMPS) has been designed (including the control unit) and a complete analysis about RFI effects on the control circuit operation has been carried out by computer simulations. In particular, it is pointed out that the switching activity of power transistors and RFI added to IC nominal signals excite low frequency feedbacks that modify the operation of the overall system. I. INTRODUCTION The large use of wireless communication systems like equipments for radio and TV broadcasting, portable phones, wireless local area network etc. has significantly increased environmental electromagnetic pollution. On the other hand, the continuous demand of low power electronic equipment implies a continuous reduction of the power supply. As a consequence, the amplitude of radio frequency interference (RFI) picked up by wiring structures like cables and printed circuit board traces is significantly increased and electronic circuit noise margins are continuously reduced. For these reasons, in the last decades investigations have been addressed to understand EMI-induced nonlinear phenomena in analog and digital elementary integrated circuits [1] [2]. The most remarkable effects have been observed in analog circuits including high gain stages like operational amplifiers (opamps), where RF interference drives rapid variations of electric signals over wide dynamic ranges and nonlinear active and passive integrated devices operate RF signal distortion causing performances degradation. In particular, it has been shown that continuous wave RFI superimposed on nominal input signals generates in feedback opamp circuits a DC output offset voltage, with a magnitude depending on interference amplitude and frequency. In the presence of amplitude or frequency modulated interference, feedback opamps demodulates RFI [3]. Similar phenomena are experienced in the presence of substrate voltage bounce [4]. In the last years the research activities have been focused on the design of elementary building blocks and system on chip intrinsically immune to EMI [5] and a specific attention has been devoted to understand EMI-induced operation failures in last generation smart power ICs, which are usually employed in electromagnetic polluted environment. In the following sections, the main phenomena induced by EMI in last generation smart power integrated circuits are discussed and the case of a flyback voltage regulator in considered in detail.