3 Replies Latest reply on Sep 11, 2015 11:04 AM by DennisS_46

    Running a 5v PSoC at 3.3v

      I've been trying to get into contact with a Cypress engineer, but 2 hours on the phone system got me nowhere, so I'm posting this here.


      I've been fooling around with a system that utilizes three CY8C29466-12PVXET PSoC1's running at 5v.  I didn't handle the programming for that system, so I don't know exactly how the chip's resources are being utilized, but I ran the system with a 3.3v supply for unrelated reasons and noticed that they were still functioning perfectly.


      I'm guessing that the M8C core runs on 3.3v internally anyways, and that that particular design did not make much use of any of the configurable blocks, which probably require the 5v supply.




      Is there any validity to running these 29466's at 3.3v?  I'd also like to know (if this is even possible) what effect lower voltages would have on their operation up near their max operating temperature at 125C.

        • 1. Re: Running a 5v PSoC at 3.3v

          The PSoC chips can run on the given voltage range up to 5V maximum. The only downgrade when the programming did not specify the operating voltage are clock precision and max operating frequencies.


          So it is not guaranteed that every project will run at a different voltage as the design says over the whole temperature range.


          Better solution would be to get hands on the sources, change the definition for the operating voltage and check for any errors or warnings when building the project anew.


          Operating a chip at max temperature will reduce the allowed power dissipation, so do not use much IO-current in that cases.





          • 2. Re: Running a 5v PSoC at 3.3v

            This discusses startup, trims that occur due to power settings, like VBG and IMO.








            A large component of Pdiss in CMOS is C x V2 x f dissipation -








            So clearly operating at lower Vdd will reduce Pdiss significantly, less than 1/2


            just due to CMOS toggling.




            Regards, Dana.

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            • 3. Re: Running a 5v PSoC at 3.3v

              CY8C29466PVXET is an automotive part. In order to guarantee operation on all specs, operation is specified only at 5.0V. The primary operational difference in the automotive version is limiting CPU clock to 12 MHz instead of 24 MHz as in all other parts. Next, the programming conditions are different. The flash is burned in "a little harder." This guarantees that the program will be retained in flash for the specified amount of time while operating at elevated automotive temperatures. As a consequence, this limits to some degree the maximum number of times that the flash can be re-written. Unless you are recording data or configurations to flash, this should not be a problem. Oscillator trims are set for 5.0V, you may have some oscillator inaccuracy at 3.3V. Low-voltage detect thresholds are set by the user for 5.0 V operation. If the designer of your project implemented low-voltage detect, then operation at 3.3V could be a problem.


              Last: I'm sorry you could get the help you needed on the phone. Send me an email:  seg@cypress.com  with your phone number. I'm located in the San Diego office and am happy to help you any time.

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