HBLXT9785HC.C2 Intel, HBLXT9785HC.C2 Datasheet - Page 163

• Manufacturer Part Number: HBLXT9785HC.C2
• Manufacturer: Intel

Specifications of HBLXT9785HC.C2

• Lead Free Status / RoHS Status: Not Compliant

LXT9785/LXT9785E
Datasheet
249241, Revision 11.0
16 April 2007
5.2.4.1
Table 51
5.2.5
Cortina Systems
Magnetic Requirements
The LXT9785/LXT9785E requires a 1:1 ratio for both the receive transformers and the
transmit transformers. The transmit isolation voltage should be rated at 1.5 kV to protect
the circuitry from static voltages across the connectors and cables. The LXT9785/
LXT9785E is a current driven transceiver that requires an external voltage (center tap) to
drive the transmit signal. In order to support the Auto-MDIX functionality of the LXT9785/
LXT9785E, the magnetic must provide a center tap for both the transmit and receive
magnetic winding, with both connected to VCCT. See the LXT9785/LXT9785E Design
and Layout Guide (249509-001) for magnetic testing with the LXT9785/LXT9785E. Before
committing to a specific component, designers should contact the manufacturer for
current product specifications, and validate the magnetics for the specific application.
Table 51
Magnetics Requirements
The Fiber Interface
The fiber interface consists of an LVPECL transmit and receive pair to an external fiber
transceiver. Both 3.3 V fiber transceivers and 5 V fiber transceivers can be used with the
LXT9785/LXT9785E. See the 100BASE-FX Fiber Optic Transceivers-Connecting a
PECL/LVPECL Interface Application Note (document number 250781) for detailed
information on fiber interface designs and recommendations for Cortina PHYs.
The following should occur in 3.3 V fiber transceiver applications as shown in
®
Rx turns ratio
Tx turns ratio
Insertion loss
Primary inductance
Transformer isolation
Differential to common mode
rejection
Return Loss
• Keep the transmit and receive pairs apart to avoid cross-talk.
• Route the transmit pair adjacent to a ground plane. The optimum arrangement is to
• Improve EMI performance by filtering the TPO center tap. A single ferrite bead rated
• The transmit pair should be AC-coupled with 2.5 V supplies and re-biased to 3.3 V
• The transmit pair should contain a balance offset in the pull-up resistors to prevent
LXT9785 and LXT9785E Advanced 8-Port 10/100 Mbps PHY Transceivers
place the transmit traces two to three layers from the ground plane, with no
intervening signals.
at 400 mA may be used to supply center tap current to all ports.
LVPECL levels
PHY-to-fiber transceiver crosstalk amplification in power-down, loopback, and reset
states (see fiber interface application note)
provides the magnetics requirements.
Parameter
Min
350
-16
-10
0.0
40
35
–
–
–
Nom
1:1
1:1
0.6
–
2
–
–
–
–
Max
1.1
–
–
–
–
–
–
–
–
5.2 General Design Guidelines
Units
dB
μH
kV
dB
dB
dB
dB
–
–
Test Condition
60 to 100 MHz
.1 to 60 MHz
30 MHz
80 MHz
Figure
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