[SI-LIST] Fw: Regarding: Usage of Magnetics...

From: "olaney@xxxxxxxx" <olaney@xxxxxxxx>
To: si-list@xxxxxxxxxxxxx
Date: Sat, 26 Dec 2009 17:59:05 GMT
The magnetics to be applied should be as close as possible to wherever the 
signal connects to the outside world, which is one reason that ethernet 
connectors with integrated magnetics are popular.  There are two basic parts to 
apply, a transformer and a common mode choke.  Transformers are used mostly to 
provide impedance conversion and galvanic isolation, and are not EMC components 
per se, although they do provide enough benefit that some designs get by with a 
transformer alone if it is properly specified and applied.  A design can use a 
common mode choke alone if the driver circuitry does not require a transformer. 
 Many designs use both for maximum EMC performance.  If you use both it is 
possible to keep the transformer at or near the silicon as long as the CMC 
stays at the connector.  Of course, this means that the filtering the 
transformer provides is compromised by whatever dirt couples into the path 
between the transformer and CMC.  This is where more general EMC considerations 
come into play, because magnetics alone are not a panacea.

Orin Laney

---------- Forwarded Message ----------
From: "karthick.murugan" <karthick.murugan@xxxxxxxxxxxxxxxxxx>
To: <si-list@xxxxxxxxxxxxx>
Subject: [SI-LIST] Regarding: Usage of Magnetics...
Date: Sat, 26 Dec 2009 17:38:43 +0530

Hi All,
I just need to clarify a small doubt on the usage of magnetics,
Whenever we are using Ethernet switch IC we should provide the magnetics to the 
ports at the chip side.
Due to some reason like signal balancing, common-mode rejection, impedance 
matching, and EMC improvement.
Consider, I am using one processor board and the respective rear board,
In that the magnetics outputs (twisted pair) are coming from the processor 
board, and it could be connected with the Ethernet switch IC that one I used in 
rear board through the rear connectors,
In Ethernet switch datasheet they mentioned all the ports should connect with 
primary side of the magnetics.
My doubt is whether we could provide one more magnetics (because already 
magnetics was given in processor board, that output is coming from the 
processor board to rear board side) 
to the ports of Ethernet switch IC, then connect to the processor side 
magnectics output, or there is no need of magnetics, if the magnetics is not 
need for that case tell me reason.

Best Regards,
Karthick.M



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[SI-LIST] Fw: Regarding: Usage of Magnetics...

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