10/100 Base-X Module for
Multi-Port Applications
ELECTRONICS INC.
EPF8116S
The circuit below is a guideline for interconnecting PCA’s EPF8116S with Level One LXT980, LXT974 and LXT975 chips for
10/100 Mb/s applications. Further details can be obtained from the chip manufacturer application notes.
Typical insertion loss of the isolation transformer is 0.5dB. This parameter covers the entire spectrum of the encoded
signals in 10/100 protocols. Under terminated conditions, to transmit a 2V pk-pk signal across the cable, you must adjust
the chips supporting resistor to get at least 2.12V pk-pk across the transmit pins.
Primary side center taps can be returned to the chip side ground plane; but more often than not, if the ground plane is itself
noisy, field experience has shown that it may worsen EMI situation. It is perhaps wiser to carefully lay the system borad
so that substantial gain in EMI suppression is obtained from the so called “common mode termination” on the cable side as
shown below. In any event, this configuration has been known to be quite successful in the field in EMI containment for
similar applications.
The phantom resistors shown around the connector have been known to suppress unwanted radiation that unused wires
pick up from the immediate environment. Their placement and use are to be considered carefully before a design is
finalized.
It is recommended that there be a neat separation of ground planes in the layout. It is generally accepted practice to limit
the plane off at least 0.05 inches away from the chip side pins of EPF8116S. There need not be any ground plane beyond
this plane.
For best results, PCB designer should design the outgoing traces preferably to be 50
Ω,
balanced and well coupled to
achieve minimum radiation from these traces.
Typical Application Circuit for UTP (only one port shown)
Rx1+
Rx1-
Tx1+
TPON1
151
149
1
3
4
5
2
TD1-
TD1+
RD1-
RD1+
Tx1-
36
37
38
40
1
2
3
6
Xmit
Rcv
LXT
TPOP1
980
TPIN1 147
974
146
975
TPIP1
RJ45*
39
EPF8116S
High Voltage
Capacitor
(2000 V)
PCA ELECTRONICS, INC.
16799 SCHOENBORN ST.
NORTH HILLS, CA 91343
CSF8116Sb Rev. 1
4/17/98
TEL: (818) 892-0761
FAX: (818) 894-5791
http://www.pca.com
PCA [ PCA ELECTRONICS INC. ]
