Crystal selection

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Several crystals are supported by the 32 MHz crystal oscillator.

The following figure shows a simple model of a crystal. It has R-L-C series components, called equivalent series resistance (ESR), motional capacitance (C0=N ), and motional inductance (LM ). The capacitor in parallel, C0 , is called the shunt capacitance, and models the package capacitance.

Figure 4. Simplified crystal model
Simplified model of a crystal

The crystal needs to have parameters ESR, C0 , and CL selected to ensure the crystal oscillator is stable.

The following figure shows the maximum allowable combinations of ESR, C0 and CL for a given crystal. A crystal is supported if that crystal's parameters fall directly on the line or below it. Crystals that are above the line are not supported.

Figure 5. Maximum allowed combinations of ESR and C0 for a given load capacitance CL
Maximum allowed combinations of ESR and CO for a given load capacitance CL