Using Crystal Oscillator Specifications as a reference:
- Pick a crystal frequency (for
example, 20 MHz).
- Check that the ESR of the crystal
<=50 Ω per specifications for 20 MHz.
- Check that the load capacitance
requirement of the crystal manufacturer is within 6 pF and 12 pF per
specifications for 20 MHz.
- As mentioned, CL1 and CL2
are in series; so, provided CL1 = CL2, effective load capacitance CL =
[CL1]/2.
- Adding board parasitics
to this results in CL = [CL1]/2 + Cstray
- Check that the maximum drive
level of the crystal >= 1 mW. If this requirement is not met, a dampening
resistor Rd can be used. Refer to DL – Drive Level on other points to consider when using Rd.