32.768KHz Tuning Forks Crystal Design Note

News / 2019-10-21

The design note of 32.768KHz tuning forks quartz crystal:

  1. Here is a quartz crystal inside the 32.768KHz tuning forks crystal, it is easy to cause breakage of the crystal when it impacted or dropped, and the crystal is ineffective. You need to consider the reliable installation of the quartz crystal and the position when you are designing. Also, try not to get close to the board edge, the device housing.
  2. Pay attention to the temperature of the soldering when you are welding by hand or machine. Quartz crystal is sensitive to temperature, the temperature during soldering should not be too high, and the heating time should be as short as possible.
  3. Try to shorten the trace of the quartz crystal part when you are designing. Keep the distance between the quartz crystal trace and other signal lines as far as possible. Besides, it is recommended to ground the crystal case, which is more effective in avoiding interference.
  4. Carefully choose the capacitance of CG and CD. Try to design according to the recommended values provided by the manufacturer. When the requirements of the oscillation are satisfied, the values of CG and CD can be as small as possible, which can shorten the start time of the crystal oscillator. Crystal: CL(pF)=(CDCG/CD+CG)+CS
  5. Check if the tuning forks crystal is overdriven and overdrive affects the life of the quartz crystal. If an oscilloscope test found that the output of the quartz crystal clipped and the top and bottom of the wave flattened, then it is necessary to consider whether the crystal is overdriven. We can adjust the resistance of the “r” current limiting resistor appropriately until the output is a complete sine wave.
    Look at the circuit diagram below: