IPC@CHIP - SC12
Hardware Manual v1.1 [05.11.2002]
©BECK IPC GmbH page 17 of 28
6. ETHERNET 10BASE-T
6.1 10Base-T Media Filter Placement and Termination
Placement of the termination components TPTX+ and TPTX- should be located as physically close to
the media filter as possible.
The media filter should also placed as physically close to the RJ-45 connector as possible to minimize
stray EMI transfer to the media. The trace routing is to keep the area enclosed by a circuit loop as
small as possible to minimize the incidence of magnetic coupling. However this can conflict with the
general rule of keeping trace lengths to a minimum. For example, if circuit components are positions
along the same sides of a square, the best return is back along the same three sides of the square,
NOT directly back along the fourths side. This rule must be strictly adhered to. Furthermore, there
should never be an unnecessary via feed-through inside the circuit loop. This also implies that the
circuit loop should never encircle the power/ground planes (i.e., part of the circuit loop above and part
of circuit loop below this planes).
Incorrect Layout
Correct Layout
The two traces of the pair should always be routed in adjacent channels and should be of same
length. To reduce capacitive coupling, each circuit loop should be separated from the others. Circuit
loops can be separated either by physical space (if located on the same layer) or by placement on
signal layers on the opposite side of the power/ground planes. The following signal groups should be
isolated from each other. Width of receiver trace should be 25 mil minimum to achieve 50Ohm
impedance characteristic at 10MHz. Width of transmitter trace should be 10 mil minimum to achieve
25Ohm impedance characteristic at 10MHz
To achieve optimum performance the designer must protect the magnetics from the environment. It
should be isolated from the power and ground planes.
6.2 Magnetics approved for use for 10Base-T application
Through-Hole PCB:
BEL FUSE, Inc. part no. 0556-5999-19 (http://www.belfuse.com)
Halo Electronics, Inc. Part no. FS22-101Y4 (http://www.haloelectronics.com)
Valor, Inc. part no. FL1012/1066 (http://www.valorinc.com/)
Surface-Mount PCB:
Valor, Inc. part no. SF1012 (http://www.valorinc.com/)
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