Intel 82562EX, Руководство по конструкции

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82540EP/82541(PI/GI/EI) & 82562EZ(EX) Dual Footprint Design Guide
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3.1.4 Circuit Board
Since the dielectric layers of the circuit board are allowed some reasonable variation in thickness,
the stray capacitance from the printed board (to the crystal circuit) will also vary. If the thickness
tolerance for the outer layers of dielectric are controlled within ±17 percent of nominal, then the
circuit board should not cause more than ±2 pF variation to the stray capacitance at the crystal.
When tuning crystal frequency, it is recommended that at least three circuit boards are tested for
frequency. These boards should be from different production lots of bare circuit boards.
Alternatively, a larger sample population of circuit boards can be used. A larger population will
increase the probability of obtaining the full range of possible variations in dielectric thickness and
the full range of variation in stray capacitance.
Next, the exact same crystal and discrete load capacitors (C1 and C2) must be soldered onto each
board, and the LAN reference frequency should be measured on each circuit board.
The circuit board, which has a LAN reference frequency closest to the center of the frequency
distribution, should be used while performing the frequency measurements to select the appropriate
value for C1 and C2.
3.1.5 Temperature Changes
Temperature changes can cause the crystal frequency to shift. Therefore, frequency measurements
should be done in the final system chassis across the system’s rated operating temperature range.
3.1.6 Integrated Magnetics Module
The magnetics module has a critical effect on overall IEEE and regulatory conformance. The
device should meet the performance required for a design with reasonable margin to allow for
manufacturing variation. Occasionally, components that meet basic specifications may cause the
system to fail IEEE testing because of interactions with other components or the printed circuit
board itself. Carefully qualifying new magnetics modules can go a long way toward preventing this
type of problem.
The steps involved in magnetics module qualification are similar to those for oscillator
qualification:
1. Verify that the vendor's published specifications in the component datasheet meet the required
IEEE specifications.
2. Independently measure the component's electrical parameters on the test bench, checking
samples from multiple lots. Check that the measured behavior is consistent from sample to
sample as well as meeting the published specifications.
3. Perform physical layer conformance testing and EMC (FCC and EN) testing in real systems.
Vary temperature and voltage while performing system level tests (for IEEE only).
Magnetics modules for 1000BASE-T Ethernet are similar to those designed solely for
10/100 Mbps, with the exception of four differential signal pairs instead of two for 10/100 Mbps.