5 Replies Latest reply on Oct 20, 2019 10:49 PM by VasanthR_91

    Vref of PSoC4(CY8C4247LTI-L475)

    YaKu_1055906

      Hi all,

       

      [1] Ext Vref(P1.7)

      How much  is the ampacity of Vref(P1.7) of CY8C4247LTI-L475?

       

      [2]Internal Vref(1.024V)

      Is it possible to to output the internal Vref(1.024V) outside CY8C4247LTI-L475?

      If possible, how much is the current of internal vref?

       

      Thanks,

        • 1. Re: Vref of PSoC4(CY8C4247LTI-L475)
          VasanthR_91

          Hello Yaushiro san,

           

          [1] Pin 1.7 has the current rating as the other pins in the chip. Absolute maximum of the current is 25mA as per the device characterization. But here I assume that you are trying to get the internal Vref out of this pin. So first of all the internal Vref is not strong enough source anything external to PSoC. But there are methods by which you may use the Vref.

          [2] The method is to buffer the output from the pin 1.7 using an opamp buffer. The opamp output can be used to source your external circuit. I have attached an example code I have generated for 4200M for an external device for this purpose.

           

          Best Regards,
          Vasanth

          • 2. Re: Vref of PSoC4(CY8C4247LTI-L475)
            YaKu_1055906

            Hi Vasanth san,

             

            Thank you for you update.

             

            >Absolute maximum of the current is 25mA as per the device characterization.

            I understand.

             

            I found the following description in the "8 GPIO Pins" of item in the document of the following URL.

            https://www.cypress.com/documentation/application-notes/an88619-psoc-4-hardware-design-considerations

            ---------------------------------------------------------------------------------------

            Each pin has 4-mA source or 8-mA sink capability.

            ----------------------------------------------------------------------------

             

            Therefore, I understand as follows.

            Is my understanding correct?

            ----------------------------------------------------------------------------

            Absolute maximum of the current is 25mA.

            Recomended of current is  4-mA source or 8-mA sink.

            ---------------------------------------------------------------------------

             

             

            Best regards.

            Yasu

            • 3. Re: Vref of PSoC4(CY8C4247LTI-L475)
              VasanthR_91

              Hi Yasu san,

               

              Recommended of current is  4-mA source or 8-mA are needed to be followed when you want to main VOL and VOH specifications to be met. This is for digital pins. Surely its better not to go till the absolute maximum border. But the device is guaranteed to work till that.

               

              Best Regards,

              Vasanth R S

              • 4. Re: Vref of PSoC4(CY8C4247LTI-L475)
                YaKu_1055906

                Hi Vasanth san,

                 

                Thank you for quick response.

                 

                I understand that "current is  4-mA source or 8-mA sink" is for digital pins spec.

                 

                 

                I checked your attached project(Vref_route.zip).

                I understand the routing of this project as shown below.

                 

                [3]

                In this project, P1.7 was connected to the positive input of the opamp.

                Is this purpose to connect the output of the reference buffer of SARREF to the opamp?

                (I think the internal 1.024V Vref is input to the opeamp.)

                Vref_1.024V_Output.GIF

                 

                 

                [4]

                I understand that Vref is output via the opamp.

                Therefore, I think Vref output current depends on the performance of the opamp.

                I read the datasheet of opamp.

                It is described as "1mA or 10mA output current" in the data sheet.

                 

                Therefore, I understand as follows.

                Is my understanding correct?

                ----------------------------------------------------------------------------

                Generally, Vref current is 1mA or 10mA (depending on opamp settings).

                Absolute maximum of the current is 25mA.

                (Surely its better not to go till the absolute maximum border.)

                ---------------------------------------------------------------------------

                 

                 

                Best regards.

                Yasu

                • 5. Re: Vref of PSoC4(CY8C4247LTI-L475)
                  VasanthR_91

                  Hi Yasu san,

                   

                  Your understanding is right. We are routing the voltage externally to an opamp buffer. The maximum current opamp ouput can provide is 10mA. So your maximum drive strength will be 10mA.

                   

                  Best Regards,
                  Vasanth