How to enable PLL2-SSC funcion of i.MX6Q?

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How to enable PLL2-SSC funcion of i.MX6Q?

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Contributor I

I want to use the Spread Spectrum funcfion for the EMC exam.

However, information of activation can not be found anywhere.

It is considered to be valid if i use the "CCM_ANALOG_PLL_SYS_SS register".

So,I want to  know  the role of each Bit(Stop/Step/Enable).

Do you have information?

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NXP Employee
NXP Employee

Hi,

I found the below information in the RM.

This PLL synthesizes a low jitter clock from the 24 MHz reference clock. The PLL has

one output clock, plus 3 PFD outputs. The System PLL supports spread spectrum

modulation for use in applications to minimize radiated emissions. The spread spectrum

PLL output clock is frequency modulated so that the energy is spread over a wider

bandwidth, thereby reducing peak radiated emissions. Due to this feature support, the

associated lock time of this PLL is longer than other PLLs in the SoC that do not support

spread spectrum modulation.

Spread spectrum operation is controlled by configuring the

CCM_ANALOG_PLL_SYS_SS register. When enabled, the PLL output frequency will

decrease by the amount defined in the STEP field, until it reaches the limiting frequency

in the STOP field. The frequency will then similarly return to the original nominal

frequency. The following equations control the spread-spectrum operation:

Spread.PNG

I wonde if you saw this information.

Unfortunately I could not find any example of it.

Maybe the SDK might be a good base to work.

Best Regards,

Alejandro

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