[SI-LIST] Re: Ferrite bead question
- From: Istvan Novak <istvan.novak@xxxxxxx>
- To: joel@xxxxxxxxxx
- Date: Sun, 09 Apr 2006 23:14:24 -0400
Joel,
Many times ferrite beads are used to ensure sufficient low-frequency
filtering. Noise suppression at the bit-rate frequency or at its
harmonics is relatively easy, because any small inductance provides
decent spatial isolation. At VRM switching frequencies on the other
hand we need either very large capacitances, or increased inductance
(here is where the ferrite bead comes in), or a linear regulator if a
higher supply voltage is available.
Regards,
Istvan novak
SUN Microsystems
Joel Brown wrote:
>I often see recommendations in application notes for ferrite beads on DC
>power lines. Sometimes a particular P/N is specified and sometimes just
>an impedance is given.
>Wouldn't I want to choose a ferrite bead that has the highest impedance
>possible at the frequencies of interest, and that the current rating and
>DC resistance are appropriate? Would the frequencies of interest be the
>fundamental switching frequency of the part and possibly the 3rd and 5th
>harmonics?
>Thanks - Joel
>
>
>
>
>
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