6 Replies Latest reply on Jul 31, 2018 11:35 PM by nsha

    Cap sense average current

    nirav.sciter_3233561

      Hi,

       

      We are using CY8CMBR3116-LQXIT for touch keypad interface.

       

      My question about the current consumption of chip.

       

      As you mention that "Average current consumption of 22 μA per sensor at 120-ms refresh interval" in datasheet.

       

      We did three different test to verify it.

      1. Do not configure any button or proxy sensor.

      2. Configure only one button.

      3. Configure Proxy Sensor(CS0/PS0).

      4. Proxy + 4 Button

       

      Case 1: Do not configure any button or proxy sensor, in this case average sleep current is 9uA. I don't know why its take 9uA as we dont configure and sensor.

       

      Case 2: Only one button is configured, Average current is 21uA.

       

      Case 3: Configure Proxy Sensor(CS0/PS0), Average current is 125uA.

       

      Case 4: Proxy + 4 Button configure, Average Current is 130uA.

       

       

      In our application we use proxy + 12 button and use  proxy event to wake up from sleep and in this case we are getting 130uA average current. Due to that product battery life goes down.

       

       

      Please find the attached document for configuration detail(EZ-Click) and oscilloscope wave form of above four cases.

       

       

      Let me know how can we reduce the current consumption of cypress?

       

      Thanks,

      Nirav Patel

        • 1. Re: Cap sense average current
          rzzh

          Hi Nirav,

           

          Even though there is no sensor configured, the chip will be waken up by WDT periodically. That is the reason why the average current is 9uA in this condition.

          The resolution(bits) of proximity sensor is higher than CapSense buttons in most conditions. The higher the resolution is, the more scanning/active time will be(1-bit higher, double the time will be), which will lead to more power consumption. That is the main reason why 1 proximity sensor consumes much more current than 1 button.

           

          Recommend to use as low resolution as it can be in your design. Of course 5:1 SNR(or higher) should be guaranteed.

          Increasing the scan period will help on reducing average current also.

           

          In addition, you can refer to AN85951 or MBR Design guide for more details.

           

          Thanks,

          Ryan

          • 2. Re: Cap sense average current
            nirav.sciter_3233561

            Ryan,

             

            "The higher the resolution is, the more scanning/active time will be(1-bit higher, double the time will be), which will lead to more power consumption."

             

            I have verified the scanning time by changing the resolution of proxy sensor but there is no any difference in active time, its remain same 6ms.

             

            Can we reduce current consumption by changing scanning/Active time of proxy sensor?

             

            "1-bit higher, double the time will be" - Can you explain more on that?

             

            Whats the scanning/Active time should be if we use proxy sensor(CS0/PS0) and button in our application?

             

            Please find the attached screen shot of configuration. (EZ-Click)

            EZ-Click.PNG

            Thanks,

            Nirav Patel

            • 3. Re: Cap sense average current
              rzzh

              Hi Nirav,

               

              How did you get the 6ms? You can measure the waveform on the proximity sensor. Its scanning time will be narrow dwon if you use smaller resolution.

              The scanning time is related with sense clock divider, resolution and some other paras.  In sleep mode, only proximity sensor will scan periodically if no touch and it is set as wake-up sensor. An easy way to get the scanning/active time is  monitoring the waveform on the proximity sensor.

               

              Thanks,

              Ryan

              • 4. Re: Cap sense average current
                nirav.sciter_3233561

                Ryan,

                 

                I measured wake up time between CS0/PS0 and GND with different resolution (Bits: 12, 13, 14, 15, 16). But getting same time.

                 

                Can you share the waveform of your setup?

                 

                I have CY3280-MBR3 kit.

                 

                 

                CS0_PS0.jpg

                HardwareSetup.jpg

                Thanks,

                Nirav Patel

                • 5. Re: Cap sense average current
                  user_1748457

                  The EE101 Insight-Pro at www.EE101.com does a great job measuring current for these types of designs!

                   

                  BLECurrent.jpg

                  • 6. Re: Cap sense average current
                    nsha

                    Hello,

                     

                    The resolution is fixed to 16-bit for proximity sensors, by design and that is the reason for scan time to be the same.

                    For low power, refer to Section 7 of http://www.cypress.com/file/46366/download. I hope this helps.

                     

                    Thanks,
                    Shanmathi

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