Understanding EMI and Mitigating Noise in DC/DC Converters

High-frequency conducted and radiated emissions from power converters occur based on the transient voltage (dv/dt) and transient current (di/dt) generated during hard switching. Such electromagnetic interference (EMI) is an increasingly complex issue in the design and qualification cycle, especially given the increased switching speed of power MOSFETs. 

1.EMI overview and fundamentals

                                –EMI noise coupling paths (DM & CM)

–EMI standards: EN55022 class B (industrial, comms), CISPR 25 class 5 (automotive)

–EMI measurement setup & LISN schematic

–EMI filtering, DM & CM equivalent circuits, CM noise propagation paths

2.EMI noise sources and mitigation

–“Hot” loops, parasitic inductance, magnetic fields

–SW node harmonics & voltage ringing, electric fields

–Circuit and layout techniques for EMI mitigation

3.EMI management in DC/DC converters

–Component placement, GND plane management, PCB stack-up strategies, etc.

–Practical circuit examples, EMI performance-optimized PCB layouts, EMI results

LM5145: VIN = 6V to 100V, VOUT = 5V, IOUT = 20A [PCB layout, input caps, inductor selection]

LM53635-Q1: VIN = 3.5V to 42V, VOUT = 5V, IOUT = 3.5A [HotRod package, SSFM, PCB layout]