Digital closed-loop EMI reduction in switched mode power supplies using adaptive spread spectrum technique

Abstract

Using a variable frequency, or spread spectrum clock in switched-mode power supplies is a popular method for reducing EMI in noise-sensitive applications. A system that operates with a fixed frequency-spread must inevitably be over-designed to compensate for the uncertainties in the parasitic components, as well as aging and temperature effects. In this work, a self-calibrated, adaptive spread spectrum system is simulated using an integrated boost converter in a high voltage 0.35 μm CMOS technology. The converter operates with a programmable spread of f <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">s</sub> = 100-350 kHz. The EMI spectrum is calculated from the sampled input current using a short-time FFT and compared with programmable limits based on EMC regulations. The spread is actively minimized under different conditions, while meeting EMI targets.