2 PCB Layout and Design Considerations

Even the best performing oscillator circuits and high-quality crystals will not perform well if not carefully considering the layout and materials used during assembly. Ultra-low power 32.768 kHz oscillators typically dissipate significantly below 1 μW, so the current flowing in the circuit is extremely small. In addition, the crystal frequency is highly dependent on the capacitive load.

To ensure the robustness of the oscillator, these guidelines are recommended during PCB layout:
  • Signal lines from XTAL1/TOSC1 and XTAL2/TOSC2 to the crystal must be as short as possible to reduce parasitic capacitance and increase noise and crosstalk immunity. Do not use sockets.
  • Shield the crystal and signal lines by surrounding it with a ground plane and guard ring
  • Do not route digital lines, escpecially clock lines, close to the crystal lines. For multilayer PCB boards, avoid routing signals below the crystal lines.
  • Use high-quality PCB and soldering materials
  • Dust and humidity will increase parasitic capacitance and reduce signal isolation, so protective coating is recommended