Intel 82562EX, Руководство по конструкции

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82540EP/82541(PI/GI/EI) & 82562EZ(EX) Dual Footprint Design Guide
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3.1.1.4 Temperature Stability and Environmental Requirements
Temperature stability is a standard measure of how the oscillation frequency varies over the full
operational temperature range (and beyond). Several optional temperature ranges are currently
available, including -40° C to +85° C for industrial environments. Some vendors separate operating
temperatures from temperature stability. Manufacturers may also list temperature stability as 50
ppm in their data sheets.
Note: Crystals also carry other specifications for storage temperature, shock resistance, and reflow solder
conditions. Crystal vendors should be consulted early in the design cycle to discuss the application
and its environmental requirements.
3.1.1.5 Calibration Mode
The terms “series-resonant” and “parallel-resonant” are often used to describe crystal circuits.
Specifying parallel mode is critical to determining how the crystal frequency is calibrated at the
factory.
A crystal specified and tested as series resonant oscillates without problem in a parallel-resonant
circuit, but the frequency is higher than nominal by several hundred parts per million. The purpose
of adding load capacitors to a crystal circuit is to establish resonance at a frequency higher than the
crystal’s inherent series resonant frequency.
Figure 2 illustrates a simplified schematic of the 82562EZ(EX) and the 82540EP/82541xx
controller’s crystal circuit. The crystal and the capacitors form a feedback element for the internal
inverting amplifier. This combination is called parallel-resonant, because it has positive reactance
at the selected frequency. In other words, the crystal behaves like an inductor in a parallel LC
circuit.
Figure 2. Crystal Circuit
C1 C2
LAN
Silicon
X1 or Xin
LAN
Silicon
X2 or Xout