CSF8087Gb

Rev. 1

12/2/97

High Speed LAN Interface Module

The circuit below is a guideline for interconnecting PCA’s EPF8087G with a typical 100 BX PHY chip for 100 Mb/s

applications over UTP cable. Further details of system design, such as chip pin-out, etc. should be obtained from the

specific chip manufacturer.

Typical insertion loss of the isolation transformer is 0.5dB. This parameter covers the entire spectrum of the encoded

signals in 100/155 protocols. Under terminated conditions, to transmit a 2V pk-pk signal across the cable, you must adjust

the specific chip preset template control resistors to get at least 2.12V pk-pk across the transmit side input pins.

It is recommended that system designers do not ground the receiver side center tap, via a capacitor. This may worsen

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

The pulldown resistors on unused pins of 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.

The “common mode termination” load of 75

Ω shown from the center taps of the secondary may be taken to chassis ground

via a suitable cap. This depends upon the user’s design, EMI margin, etc.

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 EPF8087G. There need not be any ground plane beyond

this point.

For best results, the 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 100 BX over UTP

100BX

PHY

RJ45*

1

2

6

3

RX+

RX-

TX+

TX-

75

75

EPF8087G

Rcv ±

Xmit ±

15

3

1

6

8

10

.01 µƒ

2 kV

.01 µƒ

2 kV

EPF8087G

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

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

13

9

16

12

Vcc

TEL: (818) 892-0761

FAX: (818) 894-5791

http://www.pcainc.com

PCA ELECTRONICS, INC.

16799 SCHOENBORN ST.

NORTH HILLS, CA 91343