57.4.9.1 Choosing a Crystal

When choosing a crystal for the 32768 Hz Slow Clock Oscillator or for the 3 MHz–20 MHz oscillator, users need to consider several parameters. Important parameters between crystal and product specifications are as follows:

• Crystal Load Capacitance
  • The total capacitance loading the crystal, including the oscillator’s internal parasitics and the PCB parasitics, must match the load capacitance for which the crystal’s frequency is specified. Any mismatch in the load capacitance with respect to the crystal’s specification will lead to inaccurate oscillation frequency.
• Drive Level
  • Crystal drive level ≥ Oscillator Drive Level. Having a crystal drive level number lower than the oscillator specification may damage the crystal.
• Equivalent Series Resistor (ESR)
  • Crystal ESR ≤ Oscillator ESR Max. Having a crystal with ESR value higher than the oscillator may cause the oscillator to not start.
• Shunt Capacitance
  • Max. crystal shunt capacitance ≤ Oscillator Shunt Capacitance (C_SHUNT). Having a crystal with C_SHUNT value higher than the oscillator may cause the oscillator to not start.