EMC guideline for synchronous buck converter design

Abstract

Synchronous buck converters generate broadband noise typically in 50 -300 MHz range. In this paper, the root cause of this broadband noise and possible coupling mechanisms are analysed. Then, a list of EMC design guideline for minimizing the broadband noise is presented. The guideline contains circuit level guideline which involves input filtering, component selection, and an effective snubber strategy using a parallel resistor and inductor. The guideline also contains layout level guideline, which involves decoupling capacitor placement, layer stackup, and minimizing exposed phase voltage area. For each suggested guideline item, an example illustrates the impact of the particular strategy through experimental results or SPICE simulations, leading to a strong reduction of broadband noise from the synchronous buck converter.

Radiation of input decoupling network typically used in switching DC-DC converters

“…This makes the input decoupling network a part of a DC-DC converter with a dominant contribution to its radiated emissions [3], [5], [6]. At the same time, it is the part of a design which is the easiest and cheapest to modify.…”

“…Radiated emissions of a DC-DC converter are a function of its numerous parameters, such as the frequency of the switching, rise time and fall time of the switching, C oss capacitance of the FET in the off-state [7], R oss resistance of the FET in the off-state [7], [8], characteristics of the PCB [3], [5], characteristics of the package [9], reverse-recovery of the diode [4], [10], level of input and output voltage and current [10], etc.…”

SPICE analysis of RL and RC snubber circuits for synchronous buck DC-DC converters

“…The PCB methods minimize the radiated fields by carefully designing the input decoupling network (dimensions of metal plates and traces, stackup of the PCB, positioning of components and vias) [3], [4]. They present an efficient and cheap solution for reducing EM interference of switching DC-DC converters.…”

Design and implementation of a compact frequency synchronisation control circuit using enable input for DC–DC converter

“…Switched mode power supplies produce conducted electromagnetic interference (EMI), which can affect other circuits and devices through power and signal wire or electromagnetic field [3][4][5]. The switching frequency and its harmonics are the main components of EMI [6]. Frequency synchronisation can be used to operate the DC-DC converter outside a critical signal frequency band of an application [7].…”