Simulating the EMI characteristics of step-down DC/DC converters

This paper addresses a complete analysis of the EMI problems associated with step down DC/DC converters and evaluate the effectiveness of solutions that aim to minimize the conducted emissions. Different simulation model of diodes are analyzed and a full converter including PCB stray elements is implemented in Simplorer. To increase the accuracy and account for higher frequencies in the conducted emissions, the coupling between circuit elements in the input filter is taken into account. If the EMI performance of the simulation model is compared with measurements, both for synchronous and non-synchronous rectification, it is concluded that the complete EMI signature can be simulated with satisfactory accuracy by a detailed model including stray elements and mutual couplings. Synchronous rectification can help to lower the conducted emission levels and a co-packaged Schottky diode in the low-side switch can decrease the emission levels even further by reducing the influence of the reverse recovery of the inherent body diode.