Data Sheet

Ethernet Controller I210 —Design Considerations
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Note: Intel recommends COG or NPO capacitors with a tolerance of ±5% (approximately
±1 pF) or smaller.
12.3.1.7 Shunt Capacitance
The shunt capacitance parameter is relatively unimportant compared to load capacitance. Shunt
capacitance represents the effect of the crystal’s mechanical holder and contacts. The shunt
capacitance should equal a maximum of 6 pF.
12.3.1.8 Equivalent Series Resistance
Equivalent Series Resistance (ESR) is the real component of the crystal’s impedance at the calibration
frequency, which the inverting amplifier’s loop gain must overcome. ESR varies inversely with
frequency for a given crystal family. The lower the ESR, the faster the crystal starts up. Use crystals
with an ESR value of 50  or better.
12.3.1.9 Drive Level
Drive level refers to power dissipation in use. The allowable drive level for a Surface Mounted
Technology (SMT) crystal is less than its through-hole counterpart, because surface mount crystals are
typically made from narrow, rectangular AT strips, rather than circular AT quartz blanks.
Some crystal data sheets list crystals with a maximum drive level of 1 mW. However, Intel Ethernet
controllers drive crystals to a level less than the suggested 0.3 mW value. This parameter does not
have much value for on-chip oscillator use.
12.3.1.10 Aging
Aging is a permanent change in frequency (and resistance) occurring over time. This parameter is most
important in its first year because new crystals age faster than old crystals. Use crystals with a
maximum of ±5 ppm per year aging.
12.3.1.11 Reference Crystal
The normal tolerances of the discrete crystal components can contribute to small frequency offsets with
respect to the target center frequency. To minimize the risk of tolerance-caused frequency offsets
causing a small percentage of production line units to be outside of the acceptable frequency range, it
is important to account for those shifts while empirically determining the proper values for the discrete
loading capacitors, C1 and C2.
Even with a perfect support circuit, most crystals will oscillate slightly higher or slightly lower than the
exact center of the target frequency. Therefore, frequency measurements (which determine the correct
value for C1 and C2) should be performed with an ideal reference crystal. When the capacitive load is
exactly equal to the crystal’s load rating, an ideal reference crystal will be perfectly centered at the
desired target frequency.
12.3.1.11.1 Reference Crystal Selection
There are several methods available for choosing the appropriate reference crystal:
• If a Saunders and Associates (S&A) crystal network analyzer is available, then discrete crystal
components can be tested until one is found with zero or nearly zero ppm deviation (with the