3 Replies Latest reply on Sep 29, 2020 11:24 PM by BragadeeshV_41

    Cint caps for 4700S magsense

    DaEr_349131

      Two questions regarding caps and types:

       

      1.

      The Cint caps on the ev-kit for magsense are 470PF 50V C0G 0805

      (Samsung, CL21B471KBANNNC)

      - are there any reasons for the 50V rating and the 'big' 0805 package?

      I have no space so would prefer to go with 0402 instead. not sure if there is some important characteristic I missed out on.

      Very little documentation around these caps in the datasheets.

       

       

      2.

      related, the CMOD for capsense is also 50V, 2200PF 5% NP0 0603

      (Murata, GRM1885C1H222JA01D), I guess no problems to reduce down to 0402,

      - but how important is NP0?

        • 1. Re: Cint caps for 4700S magsense
          GaneshD_41

          Hi,

           

          The amount of charge accumulated on the CINT capacitors is important for the operation of magsense. That is why 470pF capacitors are chosen. The voltage on the CINT capacitors on PSoC no way reaches the voltage level of 50 volts. Infact it will be less than the operating voltage of PSoC (VDDA/DDDD). So you can use capacitors with less voltage rating. No problem. Same logic applies for CMOD capacitor also.

           

          Coming to the package type, please note that there will be differences in secondary parameters like leakage resistance, inductance between 0805 and 0402 packages. However, there will not be any problem related to performance with these changes in secondary parameters if you chose capacitors from good quality vendors.

           

          Hope this helps !

          Thanks

          Ganesh

          • 2. Re: Cint caps for 4700S magsense
            DaEr_349131

            Hi Ganesh,

             

            There must have been a reason for picking 50V on the ev-kits. Could it be better derating?

             

            Would be great with just some input on 1 & 2, regarding C0G, NP0

            • 3. Re: Cint caps for 4700S magsense
              BragadeeshV_41

              Hi DaEr_349131,

               

              Voltage rating: The idea is to use a cap with voltage rating greater (at least twice) than the operating voltage. Any Cap with voltage rating greater than 10 V should be fine. Since 50 V rated cap is the most available one (also cheaper), we have used that in this board. But do not use a capacitor with voltage rating closer to the operating voltage.

               

              Dielectric: We recommend using C0G (NP0) since it has good performance (+/- 0.3 %) over temperature range (typically -55°C to +125°C). Cint/ Cmod capacitors should not change it's value over temperature as they affect the sensing performance. That is why we recommend C0G (NP0) caps with 5 % tolerance for this application.

               

              X7R capacitors are suited for decoupling capacitors placed in the VDDx pins.

               

              Regards,

              Bragadeesh