CSF8047Sb

Rev. Orig.

1/8/97

10/100 Base-X Module for

ICS 1890 & SSI 78Q2120

Multi-Port Applications

EPF8047S

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

The circuit below is a guideline for interconnecting PCA’s EPF8047S with ICS 1890 chip for 10/100 Mb/s applications.

Further details can be obtained from the chip manufacturer application notes. Connection to the alternative chip

SSI 78Q2120 is straight forward; please consult the SSI data sheet recommendations for completing this project.

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 EPF8047S. 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)

Notes : Only one port shown for Hub side connection.

ICS

1890

RJ45*

1

2

6

3

4

5

7

8

TX+

TX-

RX+

RX-

Chassis

Ground

50

Ω

50

Ω

75

Ω

EPF8047S

High Voltage

Capacitor

CM Capacitor

5Vcc

3

2

4

6

8

35

37

38

33

39

Rcv

Xmit

TEL: (818) 892-0761

FAX: (818) 894-5791

http://www.pcainc.com

PCA ELECTRONICS, INC.

16799 SCHOENBORN ST.

NORTH HILLS, CA 91343

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