PLLN and PLLI2SN multiplication factors range in stm32f407

[armindavatgaran]

Posted on May 25, 2015 at 13:13

Hello

What is range of the PLLN and PLLI2SN multiplication factors?According to pages 226 and 265 of RM0090_Rev9, their range is 192=< PLLN , PLLI2SN <= 432 , so factors below 192 aren't allowed?Thanks.

[Tesla DeLorean]

Posted on May 25, 2015 at 15:40

The VCO has a range of 192-432 MHz, and a comparison frequency for the PLL in the 1-2 MHz range.

The value N here assumes a 1 MHz comparison. What's happening here is division, technically not multiplication.

[armindavatgaran]

Posted on May 25, 2015 at 16:38

So what to do with this recommendation that the comparison frequency must be 2MHz to limit jitter? 

[Tesla DeLorean]

Posted on May 25, 2015 at 20:32

So are you measuring a lot of jitter now?

You'd set the PLL/VCO up so it's internal frequency falls in the 192-432 MHz range. So a multiplier of 96-216 from the 2 MHz comparison frequency.