Etherten part value

The EtherTen combines an Uno-equivalent Arduino-compatible board and Wiznet-based Ethernet support, along with a microSD card slot and Power-over-Ethernet support. [Product page]
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Joined:Fri Sep 13, 2013 3:35 pm
Etherten part value

Post by mfaircloth » Fri Sep 13, 2013 3:38 pm

I have been studying the etherten schematic and was stumped about the value for inductor part L3?

Great product design!

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Re: Etherten part value

Post by jonoxer » Sun Sep 15, 2013 10:25 pm

The value for that part doesn't matter much in terms of mH, the important thing is DC resistance and current rating. What you need is something like this:

High current ferrite bead inductor 0.015 ohm max (DC), 2A-3A rating.

We use an 0805 package but there are other styles too. Something like one from the BLM21 series will do the trick as a 2012 size, which is easier to manage by hand: ... _BLM21.pdf

A quick scan down that list shows the BLM21PG300SN1 may be suitable, for example.

The purpose of that inductor is to provide a low-impedance path between the USB cable shield and GND on the board, while reducing the amount of noise that can be transferred between them. You don't actually need it there at all for the circuit to work (you could just link them together directly) but it's a good design principle to minimise noise transfer.

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