SBAS495D June 2010 – August 2021 PCM9211
PRODUCTION DATA
A number of clock sources for the ADC are provided. Clock source selection is done using the ADCLK[2:0] register (Register 42h). In most applications, the onboard clock (XTI) is used, but using another clock source (such as a DIR recovered clock or AUXIN clock) is also possible. The ADC can only be used in a slave mode unless it is set to run in standalone mode.
The dividing ratio for the incoming clock (XTI) is set by using the registers XSCK[1:0], XBCL[1:0], and XLRCL[1:0] (Register 31h). These registers provide the ability to drive the device up to 192 kHz; however, the integrated ADC sample rate is only supported in the range of 16 kHz to 96 kHz.
Keep this limitation in mind when setting the registers.
The ADC maximum specified sampling frequency is 96 kHz. The maximum supported frequency of the DIR is 216 kHz. Therefore, special care must be taken when driving the ADC clock from the DIR receiver clock.
Driving the ADC clock from the DIR is done by setting Register 42h/ADCLK-001. An ADC clock limiter is set in Register 42h/ADFSLMT. This limiter only functions when the DIR is selected as the clock source.
If the DIR receives data that are over 96 kHz and generates a clock for the ADC that exceeds its specifications, then the ADC is forced into a power-down state. If the limiter is not set, the ADC will run beyond its specified limits and generate erroneous data.