Quantification of Self-Damping of Power MOSFET in a Synchronous Buck Converter


Ringing in the switching waveform of the switching power supply (e.g., synchronous buck converter) is known to cause broadband electromagnetic interference problems in the 30-300 MHz range. The measured switching waveform shows overshoot and, then, exponential decay of the ringing. It has been observed that this exponential decay rate varies significantly between using different low-side FETs; thus, the low-side FET dominates the attenuation of the ringing. This paper provides a novel method for quantifying the losses by using the measureable quantity "Ross," which is equivalent to the loss of the output capacitance Coss of the FET. This paper describes the method of measuring Ross and explains its relevance to the self-damping of the switch ringing. The method permits selection of a low-side FET to optimize the electromagnetic compatibility performances of the supply.


Electrical and Computer Engineering

Research Center/Lab(s)

Electromagnetic Compatibility (EMC) Laboratory

Keywords and Phrases

Broadband EMI; Buck Converters; Device Parameters; Exponential Decay Rates; Exponential Decays; Power MOSFET; Self-Damping; Switching Power Supplies; Switching Waveforms; Synchronous Buck Converter; Damping; Decay (Organic); Electric Power Supplies to Apparatus; Electromagnetic Compatibility; Electromagnetic Pulse; Electromagnetic Wave Interference; Electromagnetism; MESFET Devices; Power Electronics; Signal Interference; DC-DC Converters; Buck Converter Electromagnetic Interference (EMI); FET Device Parameter; Switch Ringing

International Standard Serial Number (ISSN)

0018-9375; 1558-187X

Document Type

Article - Journal

Document Version


File Type





© 2011 Institute of Electrical and Electronics Engineers (IEEE), All rights reserved.

Publication Date

01 Nov 2011