DM9081 datasheet(20/22 Pages) ETC

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DM9081

Final

Version: DM9081-DS-F01

April 22, 1997

Power Plane

The board power planes must be separated into analog and

digital portions. The +5V and ground planes can be laid

out according to the configuration shown in Figure 8. The

analog portion should be located under the analog power

pins of the DM9081 chip and the AUI logic. The digital

portion should be located close enough to the 10BASE-T

filter to attach a 0.1mF capacitor to the filter ground pin.

Extending the digital power plane under the 10BASE-T

filter is not recommended. The analog and digital power

planes should be connected at a single point with either a

1.8-2.2

Ω or 120Z ferrite bead. In the diagram below, a

47mF capacitor is used in parallel with a 0.1mF capacitor

to connect the analog and digital planes. Shielded RJ-45

connectors are recommended. The shielded pins should be

tied to the frame ground. Depending on the characteristics

of the 10BASE-T filter, either the frame ground or a void

in the planes should be extended under the filters. Consult

the filter manufacturer to determine if the frame ground is

needed to minimize the effects of cross-talk within the

filters.

Figure 8. DM9081 Device Power Plane Recommendations

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