Calculation of register value for audio PLL

[skajam66]

Hi,

I'm looking at the nrf5340 PS v1.2, page 75 & 76 regarding the audio clock PLL. Using the formulae given, I'm finding that the register value that yields the closest to 12.288MHz is 39846 (12.288005MHz). This differs from the table on P76 that gives a value of 39854. Is the PS in error or am I?

Regards,

AC

[Karl Ylvisaker]

Hello again, AC

Thank you for your patience with this.
I spoke to the developers, and they told me that the central value is not necessarily the one closest to 12.288000 MHz - the number in the PS table is actually 12.288330 MHz rounded down to 12.288 MHz. The central point here is calculated as the value being in the middle of the range between the min and max, which is why it is 39854 instead of 39846.
If you wish to generate a frequency closest to 12.288000 MHz then you should use the 39846 value, as given by the formula.

Furthermore, I also spoke to another colleague about this who told me that the difference of ~300 Hz here likely would be negatable for most practical purposes anyways.

Best regards,
Karl