4 Replies Latest reply on Jun 21, 2020 5:20 PM by taas_3144281

    About CapSense IDAC calibration method

    taas_3144281

      Hi.

       

      What are the advantages of IDAC autocalibration?

      Avoid flat spots by adjusting the baseline to 85%.

      Tuning can be simplified.

      What other advantages do you have?

       

      I understand that changes in the environment are being addressed by baseline algorithms.

       

      Also, what are some of the concerns you may have if you disable autocalibration, that is, manually configure IDAC?

       

      Best Regards.

        • 1. Re: About CapSense IDAC calibration method
          AH_96

          Hi taas_3144281

           

          The advantages are those that you have mentioned. Apart from that, one other advantage is environment compensation but it works slightly different from the baseline compensation of firmware.

           

          Lets say the device is powered ON at a different temperature than what was tuned for, then the rawcounts might get initialized to a smaller/greater value. It is possible that the raw counts might get calibrated to high 90% or low percent (lower than 75%) since IDAC is fixed.

           

          Now, in case 1 the device might saturate upon touch - thereby never reaching the finger threshold value and hence, will not trigger.

           

          In case 2 the device might hit a flat spot. While this can be avoided by methods such as PRS/SSC, this is still undesirable.

           

          It is not just temperature that can cause this. Even factors such as humidity or anything that might cause a shift in the capacitance will trigger a behavior as mentioned above.

           

          Best regards,
          Hari

          • 2. Re: About CapSense IDAC calibration method
            taas_3144281

            Dear Hari-san

             

            Thank you for your answer.

             

            Should I use auto calibration as much as possible?

            Is there an advantage of manually calibrating?

             

            Best Regards,

            Asanuma

            • 3. Re: About CapSense IDAC calibration method
              AH_96

              Hi taas_3144281

               

              In most cases, it is recommended to use auto-calibration. However, there might be some cases where manual tuning of IDAC might be required.

              One such case is liquid level sensing. In this application, we store the baseline in the flash and detect the change in raw counts with respect to this baseline. This enables detection of liquid even on power-up.

               

              This might also applicable in designs with reference sensors where this reference sensor can be used to compensate environmental changes.

               

              Best regards,
              Hari

              • 4. Re: About CapSense IDAC calibration method
                taas_3144281

                Dear Hari-san

                 

                Thank you for your answer.

                 

                Best Regards,

                Asanuma