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By default the stereo DAC operates at 250*fs, i.e. 12.000MHz (at the clock generator input clock) for 48kHz data. It is expected

that the PLL be used to drive the audio system unless a 12.000MHz master clock is supplied. The PLL can also use the I2S clock

input as a source. In this case, the audio DAC uses the clock from the output of the PLL.

Common Clock Settings for the DAC

The DAC can work in 4 modes, each with different oversampling rates, 125,128,64 & 32. In normal operation 125x oversampling

provides for the simplest clocking solution as it will work from 12.000MHz (common in most systems with Bluetooth or USB) at

48kHz exactly. The other modes are useful if data is being provided to the DAC from an uncontrollable isochronous source (such

as a CD player, DAB, or other external digital source) rather than being decoded from memory. In this case the PLL can be used

to derive a clock for the DAC from the I2S clock.

The DAC oversampling rate can be changed to allow simpler clocking strategies, this is controlled in the DAC SETUP register but

the oversampling rates are as follows:

DAC MODE

Oversampling Ratio Used

00

125

01

128

10

64

11

32

The following table describes the clock required at the clock generator input for various clock sample rates in the different DAC

modes:

Fs (kHz)

DAC Oversampling Ratio

Required CLock at DAC Clock Generator Input (MHz)

8

125

2

8

128

2.048

11.025

125

2.75625

11.025

128

2.8224

12

125

3

12

128

3.072

16

125

4

16

128

4.096

22.05

125

5.5125

22.05

128

5.6448

24

125

6

24

128

6.144

32

125

8

32

128

8.192

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