The Engineer’s Guide To EMI In DC-DC Converters (Part 3): Understanding Power Stage Parasitics
by Timothy Hegarty, Texas Instruments, Phoenix, Ariz., How2Power Today, Mar 21 2018
Focus:
In this part, the author provides a comprehensive illustration of inductive and capacitive
parasitic elements for a buck regulator circuit that affect not only EMI performance but also
switching losses. He explains the contribution of the responsible inductive and
capacitive circuit parasitics, so designers can minimize them and reduce the overall EMI
signature. In
general, a compact, optimized power-stage layout not only lowers EMI for easier regulatory
compliance, but also increases efficiency and reduces overall solution cost. Article begins by
identifying the critical loops with high slew rate currents in a buck converter power stage;
defines EMI sources, victims and coupling mechanisms; identifies the parasitic inductances and
capacitances in the buck converter power stage that affect EMI and losses; and discusses the
frequency ranges over which different power converter noise sources play a role. Finally, a
switching converter waveform is analyzed in the frequency domain to explain the effects of
circuit characteristics on the emitted noise spectrum and switch-node resonance is discussed.
What you’ll learn:
- How to understand the impact of circuit parasitics and switching loops on power converter emissions
- How to reduce EMI noise sources in synchronous buck and boost converters
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