I've a consideration on beads self resonant frequency. The beads have self resonant parameter and I wonder how it affects on my supply circuit. I have read many post and i suppose that self resonant freq is very important in circuits with DC/DC converters and other elements which work with some switching frequency, and I can't admit to situation where the switching frequency is equal or close to self resonant frequency? Am I right? What about circuits where I don't know what noise can occur in circuit? For example, I have SFP+ transciver supply circuits given by the manufacturer:
and my question is: Is self resonant frequency important in this case? What is your point?
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\$\begingroup\$ Provide a link to the data sheet to the ferrite bead in your circuit. \$\endgroup\$– Andy akaCommented May 11, 2018 at 14:37
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You will have all sorts of VDD resonances.
Start with the 22uF, and assume 4" of wire (100nH inductance). Resonance will be about 200,000Hz.
To dampen, use Rdampen = swrt(L / C) = sqrt(0.1uh/22uF) = sqrt(0.005) = 0.05 ohms, or about 100 squares of PCB foil.
answered May 12, 2018 at 16:11