10.1.3 Master Clock Source

The PCM186x family offers three different clock sources. For the highest performance, run the ADC in master mode from a stable, well-known SCK source, such as a CMOS SCK, or a external crystal (XTAL). The PCM186x is easy to hook up to a crystal, simply connect to XI and XO, and add capacitors to ground, as suggested in the XTAL manufacturer's data sheet (typically 15 pF).

External CMOS clock sources can be brought directly into the SCKI pin (for 3.3-V sources) or into the XI pin (1.8 V sources).

The PLL must be enabled if the clock source is unrelated to the audio rate. For instance, a 12-MHz USB crystal requires custom PLL settings to generate the 48-kHz rate clocks and the 44.1-kHz rate clocks required by many audio systems. An example with a 12-MHz clock is shown in Software-Controlled Devices Manual PLL Calculation.

For timing limits on XTAL and SCKI, see the Specifications section.