5 Replies Latest reply on Jul 3, 2014 5:30 AM by userc_2334

    20732S XTAL (32KHz)

    userc_2334


      Has anyone looked at routing out the 32.768KHz crystal with the 732S (SIP) module.  It looks like it has to come all the way around the module to get to the crystal. Seems like a really noisy route. Any suggestions?

      Thanks

        • 1. Re: 20732S XTAL (32KHz)
          jota_1939431

          Hello wayne,

           

          I assume you are reading the BLOG on 20732S Layout:

           

          Sample BCM20732S PCB Layout

           

          The Module antenna should be placed towards the end of the PCB or maximum efficiency.

           

          I will inquire as to the XTAL position in the layout.

           

          Thanks

           

          JT

          • 2. Re: 20732S XTAL (32KHz)
            MichaelF_56

            JT is tied up this afternoon, so I thought I'd share the answers he received back regarding your question about Xtal placement.

             

            First off, the BCM20732S was designed for both LPO pins as normal GPIO signals.

             

            If an external LPO is required, here's the two proposals we received back from the internal team:

             

            1.

            "Place LPO crystal and route traces under BCM20732S, as we know, it is difficult to have enough space to protect other signals from LPO signals when we are bringing out signals from SiP. But this arrangement should be completed by double side placement & SMT."

            pic1.png

             

            2.

            "Bring out traces with option B of application note and place LPO crystal closed to the LPO pins of BCM20732, and Enlarge the spaces between LPO traces and other signaling traces as possible.  Enhanced ground plane (marked in Green in below pic), must not be the same level as External LPO Crystal, in order to protect ground plane. It is recommended that two layers PCB design is minimum, one layer for Ground Plane, another layer for Crystal routing." 

            pic2.png

            • 3. Re: 20732S XTAL (32KHz)
              userc_2334


              I tend to like the second solution beter as I want avoid COBS if possible. However, I am still perplexed as to what I should do with GRND points for the caps surrounding the xtal.

              Can I just punch two small vias into the internal GRND plane for he connection?

              TNX W

              • 4. Re: 20732S XTAL (32KHz)
                jota_1939431

                Hello wayne,

                 

                Have you completed the layout of your board?

                 

                Did you have any issues with the Caps and XTAL placement and did you end up using the vias?

                 

                Please look at the BLOG post: Sample BCM20732S PCB Layout

                 

                Please let us know if this helped.

                 

                Thanks

                JT

                • 5. Re: 20732S XTAL (32KHz)
                  userc_2334

                  I did complete the layout and managed to place the vias for the XTAL outside the reserved GRND plane area.

                  Thanks,

                  Wayne

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