Fast Ethernet 10/100 Quad Transceivers — LXT974/LXT975
3.2
Magnetics Information
The LXT974/975 requires a 1:1 ratio for the receive transformers and a 2:1 ratio for the transmit
transformers as shown in Table 21. The transformer isolation voltage should be rated at 2 kV to
protect the circuitry from static voltages across the connectors and cables.
Refer to the Magnetic Manufacturers Cross Reference Guide (Application Note 73) for a list of
suitable magnetic manufacturers and part numbers. The latest version is located on the Intel web
site (http://developer.intel.com/design/network/). Suitable Magnetic part numbers are provided as a
reference only. Before committing to a specific component, designers should contact the
manufacturer for current product specifications, and validate the magnetics for a specific
application.
3.2.1
Magnetics With Improved Return Loss Performance
Intel is working with magnetic vendors to develop magnetic modules with improved return loss
characteristics. These improved magnetics simplify the design requirements for meeting ANSI
X3.263 return loss specifications.
Table 21. Magnetics Requirements
Parameter
Min
Nom
Max
Units
Test Condition
Rx turns ratio
–
–
1 : 1
–
–
–
Tx turns ratio
2 : 1
–
–
Insertion loss
0.0
350
–
1.1
–
dB
µH
kV
dB
dB
dB
dB
dB
dB
80 MHz
Primary inductance
Transformer isolation
–
2
–
40
35
–
–
–
.1 to 60 MHz
60 to 100 MHz
30 MHz
Differential to common mode rejection
Return Loss - Standard
–
–
–
-16
-10
-20
-15
–
–
80 MHz
–
–
30 MHz
Return Loss - Improved
–
–
80 MHz
Datasheet
43
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