Radiated EMI is generated by the high di/dt from pulsing currents in switching converters. The larger the 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 the path. In buck converters, the pulsing current path is from the VIN side of the input capacitors through the HS switch, through the LS switch, and then returns to the ground of the input capacitor.

High-frequency ceramic bypass capacitors at the input side provide primary path for the high di/dt components of the pulsing current. Placing ceramic capacitors as close as possible to the VIN and PGND pins is the key to EMI reduction.

The PCB copper connection of the SW pin to the inductor must be as short as possible and just wide enough to carry the LED current without excessive heating. Short, thick traces or, copper pours (shapes), must be used for high current conduction path to minimize parasitic resistance. Place the output capacitor close to the CSN pin and grounded closely to the PGND pin.