8.3.4.2 Clock Slave Mode with 4-Wire Operation (SCLK, MCLK, LRCK/FS, SDIN)

The TAS3251 device requires a system clock to operate the digital interpolation filters and advanced segment DAC modulators. The system clock is applied at the MCLK input and supports up to 50 MHz. The TAS3251 device system-clock detection circuit automatically senses the system-clock frequency. Common audio sampling frequencies in the bands of 32 kHz, (44.1 – 48 kHz), (88.2 – 96 kHz) are supported.

In the presence of a valid bit MCLK, SCLK and LRCK/FS, the device automatically configures the clock tree and PLL to drive the miniDSP as required.

The sampling frequency detector sets the clock for the digital filter, Delta Sigma Modulator (DSM) and the Negative Charge Pump (NCP) automatically. Table 3 shows examples of system clock frequencies for common audio sampling rates.

MCLK rates that are not common to standard audio clocks, between 1 MHz and 50 MHz, are supported by configuring various PLL and clock-divider registers directly. In slave mode, auto clock mode should be disabled using P0-R37. Additionally, the user can be required to ignore clock error detection if external clocks are not available for some time during configuration, or if the clocks presented on the pins of the device are invalid. The extended programmability allows the device to operate in an advanced mode in which the device becomes a clock master and drive the host serial port with LRCK/FS and SCLK, from a non-audio related clock (for example, using a setting of 12 MHz to generate 44.1 kHz [LRCK/FS] and 2.8224 MHz [SCLK]).

Table 3 shows the timing requirements for the system clock input. For optimal performance, use a clock source with low phase jitter and noise. For MCLK timing requirements, refer to the Serial Audio Port Timing – Master Mode section.