Ethernet (LAN) transformers needed for LXT971 / LXT972 chips

Posted on Friday, August 17th, 2007

An email came in yesterday from a customer on the west coast looking for magnetics (wound torroids for impedance matching) for the LXT971 and LXT972 "PHY" chips (physical layer transceivers) from Intel - formerly Level One, now Cortina Systems. These are very popular chips for use in just about any electronic circuit design that needs a single (one) 10/100 baseT lan/ethernet connection. Why are they so popular? Here is what Intel has to say: The following list provides key features of the LXT971A/972A:
• 3.3V operation
• 10BASE-T and 100BASE-TX using a single RJ-45
• 100BASE-FX (LXT971A only)
• Auto-negotiation and parallel detection support
• Low-power consumption (300 mW typical)
• Low-power Sleep mode (LXT971A only)
• Full MII interface with extended registers
• Configurable via MDIO serial management port or hardware control pins
• Integrated, programmable LED drivers

To find all data sheets application notes and design guides for these chips, go to http://www.cortina-systems.com/products/view/35

Anyway, getting back to the magnetics for these units, the app note recommend:

Turns Ratio: Rx = 1:1, Tx = 1:1
BelFuse Part #'s: Commercial Temp S558-5999-T7, Industrial S558-5999-T5

These transformers from BEL (Bel Fuse) can be found on our website at:
http://arcadiansales.com/bel-fuse-inc/discrete-magnetics-for-lan-ethernet-or-telecom/S5585999T7F/
http://arcadiansales.com/searchbypartnumber_details.php?part_number=S5585999T5F

You'll notice that these part numbers have a " -F " on the end. That suffix denotes "lead-free" or RoHS compliant version.

In addition, i'd like to recommend an RJ45 connector for use with these magnetics. Check out the Stewart Connector # SS-6488-NF at this link...
http://arcadiansales.com/bel-fuse-inc/passive-rj45-or-cat5-cat6-connector-jack-or-plug/SS6488NF/

Lastly, keep in mind that when Level One came out with these parts, ICM or integrated connector modules, like the MagJack from Bel Fuse, were not popular yet. This a a combination RJ45, ethernet magnetics, resistors, capacitor and LED's. That said, today i'd highly recommend taking a look at a "MagJack" type solution if i was using an LXT971 or LXT972 chip. Specifically, i'd check out the 08B0-1X1T-06-F1 and 08B0-1X1T-36-F1 from Bel Fuse. the -06 is good for 0-70 degrees C and the -36 is good for -40 to +85 degrees C. Check them out at the links below...
http://arcadiansales.com/belbel-fusestewart-connector/rj45-connector-with-ethernet-andor-poe---poeplus/08B01X1T06F1/
http://arcadiansales.com/searchbypartnumber_details.php?part_number=08B01X1T36F1

If anybody out there needs any assistance with magnetics for 10/100 ( or gigabit, or 10 gig) designs, don't hesitate to contact me at mikec@arcadiansales.com

-Mike Crudele
ARCADIAN SALES
WWW.ARCADIANSALES.COM