Choosing a ferrite bead for Ethernet interface

Discussion in 'General Electronics Chat' started by ill_switch, Mar 25, 2010.

  1. ill_switch

    Thread Starter New Member

    Mar 8, 2010
    5
    0
    Hello all,

    I'm designing an Ethernet interface to talk to an Arduino that will use an ENC28J60 chip. Datasheet here:

    http://ww1.microchip.com/downloads/en/DeviceDoc/39662c.pdf

    On page 7 it describes having a ferrite bead between 3v3 and a certain point on the circuit for EMI suppression. The ONLY info given on the part is that it "needs to be rated for at least 80mA."

    This will show my ignorance, but I'm having a really hard time selecting a part, since I've never worked with a circuit that included a ferrite bead in this manner before.

    There are a few commercial implementations similar to what I'm doing:

    http://www.nuelectronics.com/estore/index.php?main_page=product_info&products_id=4

    Seeedstudio used to have one in their webstore with EAGLE project files but it's not there anymore.

    At any rate, neither of those implementations give any specifics on the part they use, except that it's an SMT part.

    I'm looking at Mouser trying to pick a part for my project and I'm 110% confused. How do I pick a suitable part? Can someone suggest a part?

    Reasonbly-sized through hole or SMT would be great.
     
  2. rjenkins

    AAC Fanatic!

    Nov 6, 2005
    1,015
    69
    I used to just buy bags of bare ferrite beads and put them on offcuts of component wire, but I just checked a supplier and they list thousands of pre-wired variations..

    Any part that has visible turns of wire through it should be fine, or bare cores and add some tinned or enamelled wire yourself.

    Something like this should be fine:
    http://uk.farnell.com/fair-rite/2961666671/inductor-wound-bead-600z/dp/1191314

    Just had another look and found the bare beads:
    http://uk.farnell.com/fair-rite/2643000701/emi-suppression-bead/dp/1163262

    They are 3.5mm or about 1/8" diameter. Just thread on a wire and you have an inductor.
     
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