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.

CSA2162

Rev. B1

5/9/97

10 Base-T Interface Module for Multiport

Repeater Applications

Typical Application Circuit for UTP with external Resistor Network

E L E C T R O N I C S I N C .

EPA2162

MACE

AMD

79C940

RJ45*

3

6

2

1

TXD+

TXP+

RX+

RX-

EPA2162

TX+

TX-

RX-

1

5

2

422

Ω

R1=61.9

Ω

61.9

Ω

R2=422

Ω

TXP-

TXD-

Notes : Pin outs shown are for hubs/repeaters only

for NIC swap pins 1-2 with 3-6.

Chassis

Ground

8

7

4

5

9

10

7

3

RX+

8

4

TEL: (818) 892-0761

FAX: (818) 894-5791

http://www.pcainc.com

PCA ELECTRONICS, INC.

16799 SCHOENBORN ST.

NORTH HILLS, CA 91343

100

Ω