The new nRF52 series from Nordic Semiconductors incorporates a powerful yet low-power ARM© Cortex™-M4 processor, along with a 2.4 GHz RF transceiver. The processor's high-frequency crystal oscillator is controlled by an external 32 MHz crystal, and can utilize an optional 32.768 kHz crystal for greater accuracy and lower average power consumption.
Seiko Epson offers both a 32 MHz crystal for the mandatory clock and a 32.768 kHz crystal for the clock used in power-saving systems. Two 32 MHz crystals are available: the FA-20H type with a pack of four 2.5 x 2 mm pads and the FA-128 type with a pack of two 1.6 mm pads. Their frequency stability is +/-10 ppm over a temperature range of -20 to +75°C. For the 32.768 kHz clock, the standard FC-135 type with 3.2 x 1.5 mm pads and 20 ppm stability is a good solution.
