3 Replies Latest reply on Aug 14, 2014 4:26 AM by user_14586677

    Realistic low power usage?

    chris.jones

      Hi all,

         

      I am doing a feasibility study for a product change to CapSense.  The product spec calls for 1 uA sleep current.  I see that the datasheet for one PSoC (CY8C20437) gives the following current numbers:
      --1.1 uA for sleep
      --0.1 uA for deep sleep
      --28 uA "in run time" for scanning a single CapSense sensor

         

      However, we all know that datasheets are.....well, let's say, "optimistic".  In doing a little bit of playing around based on this article and this app note AN47310, I have gotten my power consumption down to ~200 uA (from 2 mA), during sleep mode, and a little more while scanning a single sensor.  This is a far cry from the promised 1 uA, though.

         

      What I've done so far - I took a basic 9-sensor in, 8-GPIO out, simple timer circuit and:

         
            
      • Reduced clock speed IMO to 6 MHz and CPU_Clock to /4 -- this reduced my current from 2 to 1.5
      •     
      • Implemented a basic sleep mode - down to 0.2 mA while sleeping
      •     
      • Reduced the number of sensors scanned to 1
      •     
      • Turned a couple of my outputs from Strong drive to Analog Hi-Z - this didn't seem to help power consumption
      •     
      • I assume that the advice about turning analog off is inapplicable for CapSense
      •     
      • Most of the other bullet points in the article are beyond my present knowledge of PSoC (analog column clock, VC clock dividers, etc. etc.)
      •    
         

      So....my questions for the forum are:

         
            
      • Is the quoted 1 uA range actually achievable?  Has anyone done it?  Is there low-hanging fruit I have missed?
      •     
      • What about deep sleep mode?  Will it actually go to 0.1 uA?
      •     
      • Does anybody know of any further resources, examples, etc. than what I've found so far, to help with sleep / deep sleep / low power with CapSense? 
      •    
         

      N.b., I found this article, "Low and Battery power techniques with CapSense" which only refers to AN2360, "Capacitive Sensing - Power and Sleep Considerations", which is frustratingly AWOL.  Maybe it was subsumed into the Design Guide or Getting Started, but they each only have about one page, with a small amount of useful information.

         

      Also, there is AN47215, "PSoC RC Oscillator to Accurately Time Sleep Cycles", which I haven't gotten into yet because I don't need precise timing right now.

         

      As mentioned, right now I am just trying to see if we can get within a microamp or three of 1 uA average sleep current, while maintaining one CapSense line to "wake up".

         

      Thanks in advance,
      Chris

        • 1. Re: Realistic low power usage?
          chris.jones

          What's the point of having a WYSIWYG editor to post stuff, and then having what you get in the result NOT what you see in the editor?  Sigh....

             

          Anywho, I just wanted to add one more question - are there any lower-power PSoC / Capsense parts than the 20437 that I linked?  It's rather hard to find such info in a parametric search...

          • 2. Re: Realistic low power usage?
            user_1377889

            I would suggest you to create a MyCase and submit the project and schematic used to Cypress, they can really help you.

               

            On top of this page go to "Support&Community -> Technical Support -> Create a MyCase"

               

             

               

            Bob

            • 3. Re: Realistic low power usage?
              user_14586677

              Post a schematic and archive if you have not already filed a CASE.

                 

               

                 

                  

                 

                        

                 

              To create a technical case at Cypress -

                 

               

                 

              www.cypress.com

                 

              “Support”

                 

              “Technical Support”

                 

              “Create a Case”

                 

               

                 

              You have to be registered on Cypress web site first.

                 

               

                 

              Regards, Dana.