SLAU472C February 2013 – November 2023 TAS2505 , TAS2505-Q1
For lower power consumption, it is best to derive the internal audio processing clocks using the simple dividers. When the input MCLK or other source clock is not an integer multiple of the audio processing clocks, then it is necessary to use the on-board PLL. The TAS2505 fractional PLL can be used to generate an internal master clock used to produce the processing clocks needed by the DAC and Digital Effects. The programmability of this PLL allows operation from a wide variety of clocks that may be available in the system.
The PLL input supports clocks varying from 512 kHz to 20 MHz and is register programmable to enable generation of required sampling rates with fine resolution. The PLL can be turned on by writing to page 0 / register 5, bit D7. When the PLL is enabled, the PLL output clock PLL_CLK is given by the following equation:
where
R = 1, 2, 3, ..., 16 (page 0 / register 5, default value = 1)
J = 1, 2, 3, …, 63, (page 0 / register 6, default value = 4)
D = 0, 1, 2, …, 9999 (page 0 / register 7 and 8, default value = 0)
P = 1, 2, 3, …, 8 (page 0 / register 5, default value = 1)
The PLL can be turned on via page 0, register 5, bit D7. The variable P can be programmed via page 0, register 5, bits D6–D4. The variable R can be programmed via page 0, register 5, bits D3–D0. The variable J can be programmed via page 0, register 6, bits D5–D0. The variable D is 14 bits and is programmed into two registers. The MSB portion can be programmed via page 0, register 7, bits D5–D0, and the LSB portion is programmed via page 0, register 8, bits D7–D0. For proper update of the D-divider value, page 0, register 7 must be programmed first, followed immediately by page 0, register 8. Unless the write to page 0, register 8 is completed, the new value of D does not take effect.
When the PLL is enabled, the following conditions must be satisfied.
80 MHz ≤ (PLL_CLKIN × J.D × R/P) ≤ 110 MHz