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Chapter 1
Fixed Behavior Signals
Gigabit Ethernet Magnetic Requirements
The Ethernet PHY on the sbRIO-9651 SOM uses voltage-mode drivers for the MDI pairs, which
greatly reduces the power that the magnetics consume and eliminates the need for a sensitive
center tap power supply.
You must consider the following requirements for connecting center taps:
•
Do not connect the center taps of the isolation transformer on the MDI pair side to any
power source. Keep the center taps separate from each other.
•
Connect each center tap through separate 0.1
μ
F capacitors to ground. The separation is
required because the common-mode voltage on each MDI pair might be different.
Table 1-3 lists recommended magnetic characteristics.
The sbRIO-9651 SOM development kit uses the Gigabit Ethernet connector parts described in
Table 1-4.
Refer to the datasheet for the Micrel Ethernet PHY for more information about magnetic
requirements.
GBE0 Routing Considerations
NI recommends the following design practices for properly routing GBE0 signals on your carrier
board:
•
Route MDI pairs differentially with 100
Ω
differential trace impedance.
•
Length-match the positive and negative signal for each MDI data pair to within 10 mils.
Table 1-3.
Recommended Magnetic Characteristics
Parameter
Value
Test Condition
Turns ratio
1 CT : 1 CT
—
Open-circuit inductance (min)
350
μ
H
100 mV, 100kHz, 8 mA
Insertion loss (max)
1.0 dB
0 MHz to 100 MHz
HIPOT (min)
1500 Vrms
—
Table 1-4.
Gigabit Ethernet Connector Parts
Part
Manufacturer
Part Number
sbRIO-9651 SOM PHY
Micrel
KSZ9031MNXIA
Reference carrier board Gigabit
Ethernet connector
Bel Stewart Magjack
0826-1K1T-43-F