FreeLists / si-list / [SI-LIST] Re: Ferrite bead question

[Istvan Novak <istvan.novak@xxxxxxx>]

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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