---
title: "W5500 Modular jack with integrated magnetics EMI"
url: "https://maker.wiznet.io/forum/12512"
markdown_url: "https://maker.wiznet.io/forum/12512/md"
type: "Forum topic"
category: "Ethernet Chips"
author: "kampa"
created: "2017-10-17T08:52:49+09:00"
last_activity: "2017-10-22T09:56:21+09:00"
language: "en"
views: 2014
replies: 1
source: "WIZnet Makers forum (https://maker.wiznet.io/forum/)"
---

# W5500 Modular jack with integrated magnetics EMI

## Question

Asked by kampa on 2017-10-17 in Ethernet Chips.

HI All,

I have designed a board (4-layer) which is using the w5500 and the modular jack 7499210121A from Wurth. We failed EMC pre-compliance because of a 225MHz and 275MHz frequency peaks. I identified that these emissions are coming from the ethernet part of our design. It looks we have impedance mismatching. We are re-designing the board and we’ve rerouted the differential pairs. The calculated differential impedance is 100.6 Ohm and the individual track impedance is 56ohm. I don’t think that the 56ohm will cause us any issue (50ohm wasn’t easy to achieve).
The total differential pair length for the RX is 12.93mm for RX+ and 12.88mm for RX- .
The total differential pair length for the TX is 20.12mm for TX+ and 20.11mm for TX-.
What is better to do with the ground plane? Should i route the differential pair to the modular jack having ground plane underneath it or I should stop the ground plane in the edge of the modular jack connector and continue the differential routing without it?
I have attached you a photo with the routing. Where is green there isn’t ground or power planes.
Thank you in advance.

[![W5500 ethernet routing](https://maker.wiznet.io/forum_uploads/wiznet/original/2X/c/c8e66c0f7f41f22141c26da57fae3a0612651592.JPG) W5500 ethernet routing1456×892 180 KB](https://maker.wiznet.io/forum_uploads/wiznet/original/2X/c/c8e66c0f7f41f22141c26da57fae3a0612651592.JPG)

## Replies

### Reply 1 by Eugeny, 2017-10-22

Go [here](http://www.wiznet.io/product-item/w5100/), locate icon “HW design guide” and download the archive. You will find *W5100 layout guide* inside, those general application best practices should also apply to W5500.

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Source: https://maker.wiznet.io/forum/12512