LP, XT, HS Modes

The LP, XT and HS modes support the use of quartz crystals or ceramic resonators connected to the OSC1 and OSC2 pins, as shown in the figures below. These three modes select a low, medium, or high-gain setting of the internal inverter-amplifier to support various resonator types and speeds.

The LP Oscillator mode selects the lowest gain setting of the internal inverter-amplifier, and consumes the least amount of current. LP mode is designed to drive 32.768 kHz tuning-fork type crystals (watch crystals), but can operate up to 100 kHz.

The XT Oscillator mode selects the intermediate gain setting of the internal inverter-amplifier. Current consumption is at a medium level when compared to the other two modes. XT mode is best suited to drive crystal and ceramic resonators with a frequency range up to 4 MHz.

The HS Oscillator mode selects the highest gain setting of the internal inverter-amplifier, and consumes the most current. This mode is best suited for crystal and ceramic resonators that require operating frequencies up to 20 MHz.

The figures below show typical circuits for quartz crystal and ceramic resonators.

Figure 1. Quartz Crystal Operation
Notes:
  1. 1.A series resistor (RS) may be required for quartz crystals with low drive level.
  2. 2.The value of RF varies with the Oscillator mode selected (typically between 2 MΩ and 10 MΩ).
Figure 2. Ceramic Resonator Operation
Notes:
  1. 1.A series resistor (RS) may be required for ceramic resonators with low drive level.
  2. 2.The value of RF varies with the Oscillator mode selected (typically between 2 MΩ and 10 MΩ).
  3. 3.An additional parallel feedback resistor (RP) may be required for proper ceramic resonator operation.