5 Replies Latest reply on Mar 22, 2019 2:01 AM by Chva_1477726

    PSoC6 clocking


      I am busy with a design where I need to run the CM4 core at 150MHz and also use USB (device). I am using a 12MHz external crystal for the ECO in order to get 48MHz and be below the 0.25% tolerance that USB requires via the PLL. I cannot use the FLL for USB as it has a ~1% tolerance and it can also only go up to 100MHz so  cannot reach the 150MHz mark.


      I can also use the 8MHz IMO through the PLL and still make the required 0.25% tolerance for USB, but it doe not slve my 150MHz problem


      What am I missing?




        • 1. Re: PSoC6 clocking

          Hello Chris,


          You are right that FLL can a provide a frequency above 100 MHz, also is has a tolerence of 1% which is higher than that required by USB. You will have to use an ExtClk to get 48MHz (with 0.25% tolerence) . Since PSoC 6 has only one PLL, it can be used either to obtain a frequency of 150 MHz or a Frequency of 48 MHz.




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          • 2. Re: PSoC6 clocking


            You actually can use the FLL to drive the USB HFCLK if you set the coefficients manually. Even if you use the IMO. Here is how the FLL should look like:

            Also make sure that IMO is trimmed with USB.If you want to use ECO, just drop the Lock tolerance to 2 and increase the Multiplier/Reference.

            • 3. Re: PSoC6 clocking

              Is there any benefit to using an ECO instead of FLL for USB?  Are there accuracy problems with using FLL?  I want to remove the ECO in my design.  It is being used for USB only.

              • 4. Re: PSoC6 clocking

                There is no benefit, since the ECO will consume more power and the FLL will introduce accuracy errors in any case. The chip has an option to trim the IMO based on the USB (start-of-frame), so that's the preferred method to achieve the accuracy required by the USB.

                • 5. Re: PSoC6 clocking

                  Thank you all for your inputs, especially RodolfoG for the insight on the FLL, much appreciated. It will resolve my problem.