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danupp's avatar
danupp
Icon for New Contributor rankNew Contributor
4 years ago

3.3V supply voltage for PLL in Cyclone series FPGAs?

Hi, for the Cyclone series FPGAs the PLL:s require 2.5V according to datasheets. And it says that this voltage shall be present even if they are not used.

In my application I don't use the PLLs and I have a 3.3V supply for I/Os which I have tried feeding also to the PLL supply pins. I do not really want to create a 2.5V supply only for functions that I don't use.

It seems to work for me, but do you anticipate any problems supplying 3.3V here? Since I do not use the PLL functions I don't care if they are out of spec, I just want everything else to work as intended.

By the way, I am using a semi-discrete PLL instead for less noise. See https://sm6vfz.wordpress.com/2020/08/21/pll-frequency-synthesis-with-programmeable-logic/ .

3 Replies

  • Ash_R_Intel's avatar
    Ash_R_Intel
    Icon for Regular Contributor rankRegular Contributor
    4 years ago

    Which family device are you using? Please make sure that the applied voltage does not exceed the Absolute Maximum Rating specified in the datasheet. Check values of VCCA / VCCA_PLL / VCCD_PLL / VCCA_FPLL etc. related to your device.


    Regards


    • danupp's avatar
      danupp
      Icon for New Contributor rankNew Contributor
      4 years ago

      Ok, thanks, I am mainly looking at Cyclone IV and Cyclone 10LP. The datasheets for both these series say 2.5V is recommended for VCCA but 3.75V is the absolute maximum. No problem with 3.3V then?

  • Ash_R_Intel's avatar
    Ash_R_Intel
    Icon for Regular Contributor rankRegular Contributor
    4 years ago

    Yes, it should be fine to use 3.3V as it is within Absolute Max and the feature is functionally unused.


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