3 Replies Latest reply on Jul 28, 2020 2:16 AM by VasanthR_91

    ADC voltage range on PSoC3 (PSoC5)

    JoMa_1461231

      Hi@all,

       

      In a project we use the PSoC3 20bit Del-Sig ADC.

      In case no sensor is connected to some sort of input channel of our electronic the value range of the ADC is left and the ADC overflows. It is very clear that there will be no value anymore that makes sense. It's also clear that normally the ADC range shouldn't be left.

      We use differential bufferered Mode (Rail-to-rail) in the ADC configuration. VDDA is 5V.

      My question is regarding destruction of the ADC block in this case. In the ADC component datasheet (Document Number: 002-22359) on page 38 it is stated that the Input voltage range (differential, buffered) is VDDA - 1 -> in our case 5V - 1 = 4V. Therefore it would be allowed to connect only 4V to the + Input of the ADC. Is this correct or is the differential Voltage between -Input Pin and +Input Pin of the ADC meant here?

      How is this related to the ADC Range an page 12 in the same document. There is stated, that the ADC Range (Rail-to-Rail Mode) can be from VSSA+100mV to VDDA-250mV?

       

      Thanks,

      jo

        • 1. Re: ADC voltage range on PSoC3 (PSoC5)
          VasanthR_91

          Hi Jo,

           

          I do have some doubts with the question? Especially the part where you have mentioned the "destruction of the ADC" . Did you mean to ask whether the device will damaged if a voltage higher than VDDA-1 is provided ? Now regarding the ADC range, the individual pin voltages levels cannot exceed the range specified in the datasheet. Additionally the to differential voltage range will be depended on the reference voltage selected on the component. To add at the end, kindly check the errata section on the limitations on the differential mode regarding at certain input range operation and resolution. There is common mode voltage range restriction in such cases.

           

          Best Regards,
          Vasanth

          • 2. Re: ADC voltage range on PSoC3 (PSoC5)
            JoMa_1461231

            Hi Vasanth,

             

            to precise my question: I am not sure what the right value for the maximum Voltage on the ADC pins is (mode: buffered, differential, VDDA=5V):

            - The range stated on page 38 -> VDDA - 1 or (4V in my case)

            - the range on page 12 (and the PSoC Creator) (VSSA + 100mV) - (VDDA - 250mV)   -> (100mV - 4,75V in my case)

             

            Which value is the correct one? I guess VDDA - 1?

             

            Thanks,

            Jo

            • 3. Re: ADC voltage range on PSoC3 (PSoC5)
              VasanthR_91

              Hi Joe,

               

              Exactly. VDDA-1 is the right value to be used. Apologies for the confusion here. We have initiated internal requests to correct the discrepancy between documents and creator.

               

              Best Regards,

              Vasanth