SLXT970AQC.B11-831643 Cortina Systems Inc, SLXT970AQC.B11-831643 Datasheet - Page 43

• Manufacturer Part Number: SLXT970AQC.B11-831643
• Manufacturer: Cortina Systems Inc

Specifications of SLXT970AQC.B11-831643

• Number Of Receivers: 1
• Data Rate: 10/100Mbps
• Operating Supply Voltage (typ): 5V
• Operating Temperature Classification: Commercial
• Operating Supply Voltage (max): 5.25V
• Operating Supply Voltage (min): 4.75V
• Mounting: Surface Mount
• Pin Count: 64
• Operating Temperature (max): 70C
• Operating Temperature (min): 0C
• Lead Free Status / RoHS Status: Not Compliant

3.3.3
3.3.4
3.3.5
3.3.5.1
Datasheet
The recommended implementation is to divide the VCC plane into two sections. The digital
section supplies power to the digital VCC pin, VCCIO pin, and to the external components. The
analog section supplies power to VCCA, VCCT, and VCCR pins of the LXT970A Transceiver.
The break between the two planes should run under the device. In designs with more than one
LXT970A Transceiver, a single continuous analog VCC plane can be used to supply them all.
The digital and analog VCC planes should be joined at one or more points by ferrite beads. The
beads should produce at least a 100Ω impedance at 100 MHz. The beads should be placed so that
current flow is evenly distributed. The maximum current rating of the beads should be at least
150% of the current that is actually expected to flow through them. A bulk cap (2.2 -10 μF) should
be placed on each side of each ferrite bead to stop switching noise from traveling through the
ferrite.
In addition, a high-frequency bypass cap (.01μf) should be placed near each analog VCC pin.
Ground Noise
The best approach to minimize ground noise is strict use of good general design guidelines and by
filtering the VCC plane.
Power and Ground Plane Layout Considerations
Great care needs to be taken when laying out the power and ground planes. The following
guidelines are recommended:
Interfaces for Twisted-Pair /Fiber
Twisted-Pair
Figure 21 on page 46
interfaces. The twisted-pair interface consists of magnetics and a 100
parallel on the device-side of the winding. On the transmit pair, a common-mode bypass capacitor
to ground is strongly recommended. A similar technique on the receive side can improve
performance in some cases, however the results are highly application specific and must be
verified. Route TREF nearby, but not in-between TPOP and TPON. A “Bob Smith” termination is
often provided for the unused signal pairs.
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•
•
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Follow the guidelines in the LXT970 Layout Guide for locating the split between the digital
and analog VCC planes.
Keep the digital VCC plane away from the TPOP/N and TPIP/N signals, away from the
magnetics, and away from the RJ-45 connectors.
The ground plane should be one continuous, unbroken plane.
Place the layers so that the TPOP/N and TPIP/N signals can be routed near or next to the
ground plane. It is more important to shield TPOP/N than TPIP/N for EMI reasons.
shows the recommended termination circuits for the fiber and twisted-pair
Intel
®
LXT970A Dual-Speed Fast Ethernet Transceiver
Ω
termination resistance in
43