Series Caps in Rx-Path

TCP/IP Chip W5500
1

Hi there.

According to all reference schematics referring W5500 there are series caps in RXP and RXN path.
e.g.
C9, C10 in
[url]http://wizwiki.net/wiki/lib/exe/fetch.php?media=products:w5500:w5500-ref-rj45with20150406.pdf[/url]

Are they mandatory for W5500?

I have to make a design which has to be compatible to a coupling device plugged into a 100 BASE-TX link. The schematic could be said as this:

W5500 === Device with caps === Switch

The cable length from and to the device will not exceed 1.5 m and the caps within the coupling device are 4.7nF and cannot be changed.

I already figured out that if I shorten the caps I’m able to establish a link with a few devices.
For testing I have a Netgear FS108 and a FS108P, the last one contains PoE. A link is established with the 108P Switch but not with the 108 one.
My circuit is not using PoE at all.
If I double the caps within the coupling device (only allowed for testing purpose) there is a link, and data transfer, with both types of switches.

So to sum up the question(s).
Are the series caps mandatory?
Can someone imagine of a way to increase compatibility to switches?

Thanks in advance

Skyfox

2

Hello.
I am Matthew, Wiznet researcher.
Sorry for late reply first.

  1. Are the series caps mandatory?
    → Series CAP is mandatory. (C9, C10)

  2. Can someone imagine of a way to increase compatibility to switches?
    → There is not enough information to understand how 4.7nF is connected and the content of the post. If you show me the schematic or configuration diagram (more detail), I think I might be able to answer how to improve the compatibility of the switch.

Thank you.