1 Reply Latest reply on Aug 1, 2012 11:15 AM by user_14586677

    Simplified PSoC schematic?

    user_62720120

      Hi,

         

       

         

      One thing I'm finding frustrating about using the PSoC 3s is that they seem to require a huge number number of capacitors and complex power connections.  For very space constrained applications, these can make things difficult. The QFN48 package apparently needs 9 capacitors, 10 power and 7 GND connections !

         

       

         

      My question are: Is every power connection really necessary?  Is every capacitor really necessary?

         

       

         

      For example, do I need the capacitor on Vddio3 if I am only going to be using the pins in that quadrant as analog inputs?  In fact, do I even need the power connection there? Could I just use one capacitor for all of the Vddio pins?

         

       

         

      On the attached image, you can see my space constrained PCB, and part of the schematic for it. On the schematic, I have removed the capacitors from two of the Vddio0 pins (13 & 24) to try to give me some space. 

         

       

         

      Hugo

        • 1. Re: Simplified PSoC schematic?
          user_14586677

          The short answer is there is no good answer.

             
             

           

             
             

          That being said look here at discussion of reasons for multiple power domains.

             
             

           

             
             

               http://www.cypress.com/?docID=37266    

             
             

           

             
             

          Its a bit art, not science.If your ports lightly loaded, current and C, you may be able to get

             
             

          away with sharing a coupling cap across several Vddios. If you are doing high precision

             
             

          analog and driving lots of C and I, probably not.

             
             

           

             
             

          Not all coupling caps are equal, look at their specs, especially z vs f. MLC and Polymer tanatalum

             
             

          the best.

             
             

           

             
             

          Good luck.

             
             

           

             
             

          Regards, Dana.