4 Replies Latest reply on Feb 8, 2013 3:54 PM by DaKn_263916

    OpAmp pins






      There are several uncomitted OpAmps on some PSoC3s


      The outputs seem to be connected to specific pins. Does this mean I can't route them to other pins? Does it mean I can't route them to other internal devices? E.G. ADC.


      The inputs also seem to be connected to specific pins, but according to the TRM, there seems to be more options for connecting them to other buses. Is there some advantage to using those specific pins rather than other pins?


      Is there any advantage to using those OpAmps rather than the ones in the SC/CT blocks?





        • 1. Re: OpAmp pins

          These ap notes may help -










          Related Application Notes


            AN54181 – Getting Started with PSoC 3
            AN60631 – PSoC 3 Clocking Resources
            AN58304 – PSoC 3 and PSoC 5LP - Pin Selection for
          Analog Designs
            AN58827 – Internal Routing Considerations for
          PSoC 3 and PSoC 5LP Analog Designs
            AN54460 – Interrupt Handling in PSoC 3
            AN60580 – SIO Tips and Tricks in PSoC 3 and
          PSoC 5LP
            AN66083 – Using Sleep and Hibernate Modes in
          PSoC 3
            AN52705 – PSoC 3 and PSoC 5LP - Getting Started
          with DMA




          Regards, Dana.

          • 2. Re: OpAmp pins

            Whenever you use one of the opamps its dedicated pins will be in use and cannot be used by another component. The router is able to connect that opamp to another pin when required, but the dedicated pins will still be in use. So the route is "hopping" from the dedicated pin to the target.


            This was used to have low-impandence connections for some of the internal devices to the outside.





            • 3. Re: OpAmp pins

              Modificatiuon to what Bob said. Just the OpAmp output pin becomes dedicated,


              not its inputs.






              Opamp Pin Selection






              The opamps are connected to the GPIOs in such a way that they can be used without


              any internal analog global busses, See Figure 12. If all connections to the opamp are


              external through the GPIOs, it is a good idea to use the dedicated pins. In many cases,


              the opamp may be used as a buffer to an internally generated signal, such as a buffer to


              a VDAC output. In this case the dedicated opamp input pins may be ignored and used for


              another purpose. After the opamp is enabled, the dedicated output GPIO will always be


              driven by the output of the opamp. This GPIO is now dedicated to the opamp output and


              cannot be used for another signal. Even if this signal is only used internally, the dedicated


              output pin will be driven by the opamp. This guarantees that the resistance between the


              opamp and GPIO pin is low, about 5 ohms. If you must use a different pin for the output,


              the dedicated output pin still outputs the signal. If the opamp is not used, it has no affect


              on the GPIOs directly connected to it. These GPIO pins operate as any of the other GPIOs


              when the opamp is disabled.  


              Regards, Dana.

              1 of 1 people found this helpful
              • 4. Re: OpAmp pins

                Makes one wonder if the output pin can be over-ridden with a register write.




                After all out R in the path of an OpAmp output, its effective Zo becomes divided


                by loop gain.




                Regards, Dana.