EPF8001GM Datasheet, PDF (2/2 Pages) PCA ELECTRONICS INC. – 10/100 LAN Interface Module with Common Mode Termination

ELECTRONICS INC.
10/100 LAN Interface Module with
Common Mode Termination
THIS PART IS PRODUCED UNDER LICENSE FROM NATIONAL SEMICONDUCTOR CORP.
The circuit below is a guideline for interconnecting PCA’s EPF8001GM with National DP83840A and DP83223(A) twister
chip set for 10/100 Mb/s applications. Further details can be obtained from the chip manufacturer application notes.
Please consult PCA for applications help regarding the SSI78Q2120 or ICS1890 series parts or consult with the respective
application notes.
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 TXREF resistor of the twister chip to get at least 2.12V pk-pk across pins 16-15.
Note that this part only has one series common mode choke and a shunt choke with `its center tap available at pin 12 for
the “common mode termination” via an external 75Ω. This shunting effect may not meet the system EMI containment
needs; in such a case, system designers are highly encouraged to investigate the use of EPF8017GM, a part built
specifically with better common mode attenuation for applications with DP83840A and DP83223(A). Designers of the TSC
or the ICS parts may look into EPF8010GM for similar enhanced common mode attenuation.
System designers need not take the receiver side center tap to ground, via a capacitor. This may worsen EMI, specifically
if the secondary “common mode termination” is pulled to chassis ground as shown.
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.
The “common mode termination” load of 75 Ω shown from the center taps of the secondary may be taken to chassis ground
via a cap of suitable value. This depends upon 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 EPF8001GM. 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.
Typical Application Circuit for UTP (Excerpts from NSC DP83840A application notes)
+
RXD
-
+
TXU
-
0.10µF {Note 1}
1000pF
0.1µF
{Note 1}
12.1Ω
12.1Ω
1000pF
+
TD
-
TXO
PMRD
RXI
DP83840A
DP83223
SD PMID
+
SD
-
+
RD
-
1
5
12
2
16
14
6
15
7
11
10
EPF8001GM
75Ω
75Ω
50Ω
50Ω
2000V
Isolation Cap
8
7
5
4
RJ45*
6
3
2
1
Chassis
Ground
Other pull down/up resistors not shown, for clarification please refer to National’s application notes.
Notes : 1. See text above for clarification.
2. *NIC Side is shown. Hub side connections will have crossover swapping pins 3-6 & 1-2.
PCA ELECTRONICS, INC.
16799 SCHOENBORN ST.
NORTH HILLS, CA 91343
CSF8001GMb Rev. - 1/23/97
TEL: [phone]
FAX: [phone]
http://www.pcainc.com