sm840051 Micrel Semiconductor, sm840051 Datasheet - Page 8

• Manufacturer Part Number: sm840051
• Description: Gigabit Ethernet Ultra-low Jitter Clock Synthesizer
• Manufacturer: Micrel Semiconductor

Micrel, Inc.
Total capacitance seen by crystal = CL =
May 2010
(Ct1 + Cb1 + Cd1)
1
1
+
(Ct2 + Cb2 + Cd2)
1
8
Example:
CL = 18pF, Cb = 2pF, Cd = 4pF
Trim Cap = Ct = 2 (18pF) - (2pF +4pF) = 30pF
The SM840051 has been characterized with 19.44MHz,
18pF parallel resonant crystal. The trim capacitors Ct1 and
Ct2 were optimized to minimize the ppm error.
To minimize the board capacitance, a short trace from pin
to crystal footprint without vias is desirable. It is preferable
to have ground shielding or distance between the crystal
traces and noisy signals on the board.
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M9999-050710-C
SM840051