Impact of PCB design on switching noise and EMI of synchronous DC-DC buck converter

Synchronous DC-DC buck converters operate under a few MHz but generate broadband noise up to GHz range due to its switching operation. The noise causes EMI problem through radiation and switching noise at the converter output from direct conduction. To control EMI and switching noise at the converter output, proper PCB design plays a critical role. This paper evaluates three types of GND plane layout and three types of high-voltage AC node layout for synchronous DC-DC buck converter test benches with 4-layer stack-up PCB. Transverse electromagnetic (TEM) cell measurement and time-domain measurement of switching noise at the converters output were performed for the evaluation. The source of EMI, switching noise and magnitude difference over layouts were analyzed by the impedance measurement on the test benches.

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