DM9000
ISA to Ethernet MAC Controller with Integrated 10/100 PHY
44
Final
Version: DM9000-DS-F02
June 26, 2002
11. Application Notes
11.1 Network Interface Signal Routing
Place the transformer as close as possible to the RJ-45
connector. Place all the 50
Ω
resistors as close as
possible to the DM9000 RXI
±
and TXO
±
pins. Traces
routed from RXI
±
and TXO
±
to the transformer should run
in close pairs directly to the transformer. The designer
should be careful not to cross the transmit and receive pairs.
As always, vias should be avoided as much as possible.
The network interface should be void of any signals other
than the TXO
±
and RXI
±
pairs between the RJ-45 to the
transformer and the transformer to the DM9000.. There
should be no power or ground planes in the area under the
network side of the transformer to include the area under the
RJ-45 connector. (Refer to Figure 4 and 5) Keep chassis
ground away from all active signals. The RJ-45 connector
and any unused pins should be tied to chassis ground
through a resistor divider network and a 2KV bypass
capacitor.
The Band Gap resistor should be placed as physically close
as pins 25 and 26 as possible (refer to Figure 1 and 2).
The designer should not run any high-speed signal near the
Band Gap resistor placement.
11.2 10Base-T/100Base-TX Application
DM9000
RXI+
RXI-
TX0+
TX0-
BGGND
BGRES
Transformer
RJ45
3
6
8
1
4
5
2
7
1:1
1:1
75
Ω
1%
75
Ω
1%
75
Ω
1%
75
Ω
1%
3.3V AVCC
0.1µF
0.1µF
0.1µF
0.1µF
0.1µF/2KV
Chasis GND
6.8K
Ω
, 1%
50
Ω
1%
50
Ω
1%
50
Ω
1%
50
Ω
1%
3.3V AVDD
AGND
AGND
AGND
AGND
29
30
33
34
26
25
AGND
Figure 11-1