SNVSA47C February 2016 – December 2020 LM5165
Radiated EMI generated by high di/dt components relates to pulsing currents in switching converters. The larger area covered by the path of a pulsing current, the more electromagnetic emission is generated. The key to minimize radiated EMI is to identify the pulsing current path and minimize the area of that path.
The critical switching loop of the power stage in terms of EMI is denoted in Figure 10-1. The topological architecture of a buck converter means that a particularly high di/dt current effective path exists in the loop comprising the input capacitor and the LM5165's integrated MOSFETs, and it becomes mandatory to reduce the parasitic inductance of this loop by minimizing the effective loop area.
The input capacitor provides the primary path for the high di/dt components of the high-side MOSFET's current. Placing a ceramic capacitor as close as possible to the VIN and GND pins is the key to EMI reduction. Keep the trace connecting SW to the inductor as short as possible and just wide enough to carry the load current without excessive heating. Use short, thick traces or copper pours (shapes) for current conduction path to minimize parasitic resistance. Place the output capacitor close to the VOUT side of the inductor, and connect the capacitor's return terminal to the LM5165's GND pin and exposed PAD.