Today’s Ethernet (LAN) circuits require impedance matching transformers to make the proper connection between the signal coming in from the datacom cable and the PHY, or PHYsical Layer Transceiver, chip.

For Ethernet (LAN) applications, such as 10 baseT, 10/100 base T Fast Ethernet, and 1000 baseT gigabit ethernet, the magnetic modules can be described as follows. Small ferrite “cores” (transformers and optional common mode chokes) that are wound with various combinations of copper wire to achieve a certain “turns ratio” are placed within a surface mount SOIC type plastic module with a lead-frame that looks much like a small IC, or integrated circuit. Some of these modules include common mode chokes for EMI noise suppression, and some do not.

The most popular Ethernet Magnetics include:

Single Port 1000 baseT gigabit, 1:1 turns ratio applications	PHY chips in this category include, but are not limited to: BCM5461, 82566, 82563, 82571, 82572, 82573, 88E1000, 88E1010, 88E1011, and 88E1111
S558-5999-M8-F	S558-5999-M8 / S558-5999-M8-F (.48 x .7 inch, 24 pin pkg, 8 cores, for Marvell)
S558-5999-P3-F	S558-5999-P3 / S558-5999-P3-F (.48 x .7 inch, 24 pin pkg, 12 cores, for Broadcom)
Two (Dual) Port 1000 baseT gigabit, 1:1 turns ratio applications	PHY chips in this category include, but are not limited to: BCM5482,BCM5464, BCM5466,BCM5488, BCM5490, 82564, 82571, 88E1020, 88E1040, 88E1041, 88E1042, 88E1145, and 88E1180.
S558-5999-Q2-F	S558-5999-Q2 / S558-5999-Q2-F (.48 x 1.1 inch, 48 pin pkg, 8 cores)
S558-5999-Q3-F	S558-5999-Q3 / S558-5999-Q3-F (.48 x 1.1 inch, 48 pin pkg, 12 cores)
Single Port 10/100, 1:1 turns ratio applications	PHY chips in this category include, but are not limited to: LXT970, LXT871, LXT972, AC101, Am79C874, BCM5201, BCM5202, and CS8952.
	S558-5999-T7 / S558-5999-T7-F (SOIC 16, commercial temp 0 to 70c) S558-5999-U7 / S558-5999-U7-F (SOIC 16, comm. temp, 0 to 70c, reverse pin-out) S558-5999-W2 / S558-5999-W2-F (SOIC 16, comm. temp, auto mdix) S558-5999-46 / S558-5999-46-F (.4 x 1inch, 16 pin package, comm. temp, for 5V “PHY”)
Four (Quad) Port 10/100, 1:1 turns ratio applications	PHY chips in this category include, but are not limited to: BCM5225, BCM5226, BCM5227, BCM5228, LXT9785, 88E3060, 88E3061, 88E3080, 88E3081, and 88E6050.
S558-5999-Q9-F	S558-5999-Q9 / S558-5999-Q9-F (.48 x 1.1 inch, 40 pin pkg, comm temp, auto mdix)
Single Port 10 BaseT applications	PHY chips in this category include, but are not limited to: LXT905, LXT908, DP83907, DP83953 and CS8900A.
S553-5999-86-F	S553-5999-86 / S553-5999-86-F (1:1 TX, 1:2 RX turns ratio SOIC 16)
S553-5999-F5-F	S553-5999-F5 / S553-5999-F5-F (1:1 TX, 1:2.5 RX turns ratio SOIC 16)