8.3.2 Phase-Locked Loop (PLL) and Clock Generation

The device has a smart auto-configuration block to generate all necessary internal clocks required for the ADC modulator and the digital filter engine used for signal processing. This configuration is done by monitoring the frequency of the FSYNC and BCLK signal on the audio bus.

The device supports the various output data sample rates (of the FSYNC signal frequency) and the BCLK to FSYNC ratio to configure all clock dividers, including the PLL configuration, internally without host programming. Table 6 and Table 7 list the supported FSYNC and BCLK frequencies.

The status register ASI_STS, P0_R21, captures the device auto detect result for the FSYNC frequency and the BCLK to FSYNC ratio. If the device finds any unsupported combinations of FSYNC frequency and BCLK to FSYNC ratios, the device generates an ASI clock-error interrupt and mutes the record channels accordingly.

The device uses an integrated, low-jitter, phase-locked loop (PLL) to generate internal clocks required for the ADC modulator and digital filter engine, as well as other control blocks. The device also supports an option to use BCLK, GPIO1, or the GPIx pin (as MCLK) as the audio clock source without using the PLL to reduce power consumption. However, the ADC performance may degrade based on jitter from the external clock source, and some processing features may not be supported if the external audio clock source frequency is not high enough. Therefore, TI recommends using the PLL for high-performance applications. More details and information on how to configure and use the device in low-power mode without using the PLL are discussed in the TLV320ADCx140 Operation for Low-Power Critical Applications application report.

The device also supports an audio bus master mode operation using the GPIO1 or GPIx pin (as MCLK) as the reference input clock source and supports various flexible options and a wide variety of system clocks. More details and information on master mode configuration and operation are discussed in the Configuring and Operating the TLV320ADCx140 as an Audio Bus Master application report.

The audio bus clock error detection and auto-detect feature automatically generates all internal clocks, but can be disabled using the ASI_ERR, P0_R9_D5 and AUTO_CLK_CFG, P0_R19_D6, register bits, respectively. In the system, this disable feature can be used to support custom clock frequencies that are not covered by the auto detect scheme. For such application use cases, care must be taken to ensure that the multiple clock dividers are all configured appropriately. Therefore, TI recommends using the PPC3 GUI for device configuration settings; for more details see the TLV320ADCx140 Evaluation module user's guide and the PurePath™ console graphical development suite.