External Crystal Load Capacitor Requirement for the CY22381

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    Question: Can we have external load capacitors while using a crystal as a reference input for the CY22381?



    Normally the CY22381 is configured so that external crystal load caps are not needed. However, it is fine to have external caps if the settings are adjusted appropriately. It is possible to increase the on-chip capacitance and eliminate the external caps. Always check the power rating for the crystal. CyberClocks software will automatically choose the oscillator drive strength level based on whether you have a driven or crystal reference, the parallel load capacitance of the crystal, and the reference frequency. For best results, a fundamental mode, parallel resonant crystal should be used. We have our Crystal Oscillator Topics - AN1235 application note available on our website that describes the recommended reference inputs for Cypress's PLL-based frequency synthesizers, and concludes with an error budget analysis.