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i.MX6DQ PLL2 spread spectrum.

Question asked by Satoshi Shimoda on Jan 29, 2014
Latest reply on Jun 7, 2017 by Van Sreng

Hi community,

 

I want to confirm about i.MX6DQ PLL spread spectrum.

Please see my questions below.

 

[Q1]

Please see chapter 18.5.1.3.3 in IMX6DQRM Rev.1.

According to the explanation, I understand the PLL2 spread spectrum is "down spread".

Is my understanding correct?

 

[Q2]

I want to confirm how to set the spread spectrum.

If I use 528MHz PLL2 output for DDR and use -1% down spread, I have to set "Spread spectrum range" in a formula of chapter 18.5.1.3.3 to "5.28" MHz.

Is my understanding correct?

 

[Q3]

In chapter 18.5.1.3.3, "Modulation frequency" = (Fref x CCM_ANALOG_PLL_SYS_SS[STEP]) / (2 x CCM_ANALOG_PLL_SYS_SS[STOP]).

And, in chapter 18.7.5, "Frequency change step" = 24 x step / CCM_ANALOG_PLL_SYS_DENOM[B].

According to these formula, I understand there is a relationship between "Frequency change step" and "Modulation frequency" because both formula use CCM_ANALOG_PLL_SYS_SS[STEP].

And I set "CCM_ANALOG_PLL_SS[STEP] value larger, the cycle of modulation frequency will be faster.

Is my understanding correct?

 

Best Regards,

Satoshi Shimoda

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