EPA2162 Datasheet, PDF (2/2 Pages) PCA ELECTRONICS INC. – 10 Base-T Interface Module for Multiport Repeater Applications

ELECTRONICS INC.
10 Base-T Interface Module for Multiport
Repeater Applications
EPA2162
The circuit below is a guideline for interconnecting PCA’s EPA2162 with AMD 79C940 MACE 10 Base-T PHY chip over
UTP cable. Further details of system design, such as chip pin-out, etc. can be obtained from the specific chip
manufacturer. This part is designed to show excellent in band charactoristics such as insertion loss, return loss. Additional
care has been given in the design to provide the maximum common mode attenuation possible in the structure.
Typical insertion loss of the isolation transformer/filter is 0.7dB. This parameter covers the entire spectrum of the encoded
signals in 10 Base-T protocols. However, the predistortion resistor network introduces some loss which has to be taken
into account in determining how well your design meets the Standard Template requirements. Additionally, the following
need to be considered while selecting resistor values :
a. The filter needs 100 ohms termination, thus the Thevenin’s equivalent resistance seen by the filter looking into the
transmit outputs from the chip must be equal to a value close to 100 ohms. The typical driver output impedance is 5
ohms. Thus choose R1 and R2 values that are lowered by 5 ohms on each leg. Following these guidelines will
guarantee that the return loss specifications are satisfied at all extremes of cable impedance (i.e. 85 ohms to 115
ohms) while the module is installed in your system.
b. That the template requirements are satisfied under the worst case Vcc (i.e. 4.5V), will impose a further constraint on
resistor selection, in that they ought to be the minimum derived from the calculations. Add R3 for more flexibility in
setting voltage levels at the outputs.
c. Consider the effect of cable length to be expected in the given applicationfor which the design is being targeted.
Values given here provide an effective termination of 2(61.9//422)//1200 or approx. 100 ohms. Thus, bench measurement
of return loss is done by shorting all input pins of the transmit channel. This assumes, as is evident from above, that the
MACE ouput driver impendance is less than 1 or 2 ohms at most.
Note that some systems have auto polarity detection and some do not. If not, be certain to follow the proper polarity.
It is recommended that system designers ground the chip side center taps via a low voltage capacitor. It is not neccessary
to add another capacitor between this and the ground.
The pulldown resistors used around the RJ45 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 0.08 inches away from the chip side pins of EPA2162. There need not be any ground plane beyond
this point.
For best results, PCB designer should design the outgoing traces preferably to be 50 ohms, balanced and well coupled to
achieve minimum radiation from these traces.
Typical Application Circuit for UTP with external Resistor Network
TXD+
TXP+
R1=61.9Ω
R2=422Ω
MACE
AMD
79C940
TXP-
TXD-
RX+
RX-
422Ω
61.9Ω
100Ω
TX+
93
TX-
1
10 6
RJ45*
5
7
RX+
1
RX-
2
8
EPA2162
2
4578
34
Notes : Pin outs shown are for hubs/repeaters only
for NIC swap pins 1-2 with 3-6.
PCA ELECTRONICS, INC.
16799 SCHOENBORN ST.
NORTH HILLS, CA 91343
CSA2162 Rev. B1 5/9/97
Chassis
Ground
TEL: [phone]
FAX: [phone]
http://www.pcainc.com