8 Replies Latest reply on Jun 9, 2020 2:29 AM by LePo_1062026

    IDAC

    YuCh_3947976

      Hi,I use the command (IDAC_SetValue(0xFF) ) to set the value to 0xFF,but I actually measure the voltage of R1 as 4.5V and current is 220uA by multimeter.

      Anyone knows where I set it wrong?

       

        • 1. Re: IDAC
          NoriakiT_91

          There is a Vcompliance specification described in the IDAC datasheet as follows.

          GS004776.png

           

          This is the drop out voltage from the power supply (or the ground) to the IDAC output.  So, the expected maximum voltage will be 4.2V in case of VDD=5.0V

           

          Regards,

          Noriaki

          • 2. Re: IDAC
            YuCh_3947976

            May I adjust the maximum voltage in system?

            I want to get maximum voltage is 12V on R_1,have any method to realize it?

            (I use CY8CKIT-044)

            • 3. Re: IDAC
              LePo_1062026

              YuCh,

               

              The PSoC won't be able to provide more voltage than is sourced to it.  In this case VDDA on your PSoC is about 4.5V.

               

              Your settings of 621uA with R1 = 20K ohms = 0.000621A * 20000 ohms = 12.24V.   You will be limited to VDDA = 4.5V.  With R1 = 20K, the current is 4.5V/20000 = 0.000225A  = 225uA.

               

              You indicated that you want a maximum voltage of 12V.  What is the intent of this part of your design?  Are you using the IDAC to provide a controlled voltage or a controlled current?

               

              Len

              • 4. Re: IDAC
                LePo_1062026

                YuCh,

                 

                Here's a controlled voltage source using the IDAC.

                The source current from the external OP284 opamp is limited by the max source current of the opamp which is about 12mA.

                If you need significantly more current you will need to place a PNP transistor on the output of the opamp and place the feedbackof the opamp to the output of the PNP.  See diagram below.  This circuit is designed for about 1A @ 12V output.

                Len

                • 5. Re: IDAC
                  YuCh_3947976

                  Ok,thanks,I would use the upper circuit.

                  when I test the function,I want to set the current value to 0 ( IDAC_SetValue(0) )

                  it always has a minimum voltage and current on R_1(around 2.2V、334uA)

                  Don't I use the command to set value what I want?

                  • 6. Re: IDAC
                    LePo_1062026

                    YuCh,

                     

                    I want to set the current value to 0 ( IDAC_SetValue(0) )

                    Yes.  That's how you control the output setpoint.

                    I've attached a better schematic of the first circuit with your 6.8K resistor on the IDAC and a Rail-to-Rail output Opamp.  Note:  To use the opamp below to get 12V as a maximum output you need a 13V Vbat supply.

                    Here is the DC sweep of the above circuit from IDAC = 0uA to 612uA

                    Len

                    • 7. Re: IDAC
                      YuCh_3947976

                      Can you provide your project to me?

                      I want to check what's the difference.

                      thanks.

                      • 8. Re: IDAC
                        LePo_1062026

                        YuCh,

                         

                        I have no project.  What I have provided are schematics and simulation data from LTSpice.

                         

                        Len