The circuit below is a guideline for interconnecting PCA’s EPA2188B with National chips as a reference controller. Further

details of system design, such as chip pin-out, etc. can be obtained from the specific chip manufacturer.

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, note that NSC

suggest using lower values for the resistors to provide more optimum amplitude control as would be required when driving

lon cables or of varied quality unknown to the designer. Both values are shown here for your convenience. Users are

encouraged to verify which network best suits their needs with the chip manufacturer before choosing one or the other.

For the first case, a quick calculation of the effective Thevenin’s termination impedance for the filter follows:

1/R(termination)= 95

Ω.

In the second case, one gets about the same values assuming RACT ≈ 7Ω. Thus, when measuring the return loss of these

parts on the bench, it is necessary to provide a shunting resistor of approximatively 5

Ω representing the four 5Ω output

signal sources.

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. Taking the cable

side center taps to chassis via capacitors, is not recommended, as this will add cost without containing EMI. This may

worsen EMI, specifically if the primary “common mode termination” is pulled to ground as shown.

The phantom resistors shown 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 EPA2188B. There need not be any ground plane beyond

this point.

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.

CSA2188Bb Rev. -

10/7/96

10 Base-T Multiport Module with

Enhanced Common Mode Attenuation

Typical Application Circuit for UTP (Only one port shown)

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

Notes : * Pin-outs shown are for multiport, DCE configurations : e.g. Hubs, Repeaters

EPA2188B

RIC

RJ45*

3

6

2

1

TX+

TXd+

RX+

RX-

EPA2188B

TX+

TX-

RX+

RX-

TX-

TXd-

Chassis

Ground

8

7

45

62

60

56

58

86

1

2

5

7

3

4

TEL: (818) 892-0761

FAX: (818) 894-5791

http://www.pca.com

PCA ELECTRONICS, INC.

16799 SCHOENBORN ST.

NORTH HILLS, CA 91343