CyClocksRT Crystal Capacitance Calculation for CY22050, CY22150 and CY22801

Question: How does CyClocksRT calculate cyrstal capacitance for the CY22050, CY22150 and CY22801?  Should I account for board capacitance when entering a value?

 

Answer:

When configuring clock generators for use with a crystal, CyClocksRT asks the user to enter a value for the crystal load capacitance rating (CL).  It then calculates the appropriate device settings so that the crystal sees the correct load.

For the devices listed here, CyClocksRT assumes 2 pF of net board capacitance (4 pF per crystal pin).

Example: If you enter 18 pF, the software will configure the clock device for 16 pF net load to the crystal (32 pF per pin), with the assumption that the board contributes a net 2 pF (4 pF per pin).

If you determine that your board capacitance is greater than 2 pF (4 pF per pin), you should decrease the value you enter into CyberClocksRT accordingly.

Note that assumptions about board capacitance are not the same for all clock generator products.