3 Replies Latest reply on Jun 27, 2019 2:50 AM by RajathB_01

    Stop laptop providing VConn power?

    OlEr_1999891

      Hi!

       

      We have a strange problem with signal quality creating unstable video and USB 2.0 communication with one of our USB-C docking station designs. We have tried to find what is different when the effect happens and one thing that looks like is that certain laptops/ports turns on VCONN power continously so that the EMCA chip is powered all the time. We were thinking if there could be a problem with cables having the EMCA chip running all the time creating signal interference in the cable.

       

      Included two different traces from to different laptops, were one turns on VCONN power and one doesn't. Same laptop / port can at time also turn on VCONN power so it looks more like a timing thing or similar.

       

      So, question is:

      - Is it normal that a docked laptop should contiously provide VCONN power down the cable? If not normal, how can we ensure that doesn't happen?

      - Is there any possibility that the signal problem that we have could be based on the EMCA-chip and cable continuously being powered?

       

      We are also looking at other signal integrity possibilities, but it has been interesting to see that for devices that connects and that don't provide VCONN power the system is 100% stable.

       

      Included also the current configuration file for CCG4.

       

      Cheers

      Olof

        • 1. Re: Stop laptop providing VConn power?
          RajathB_01

          Hi Olof,

           

          Going through the logs, I feel there could a problem with the EMCA itself.

          According to specification, there should not be any problem with sourcing VCONN indefinitely, except that it will waste power if there is no need to communicate with SOP'/SOP"

          So I believe the notebooks are fine, the cable might be behaving strangely. Can you try with different cables? Do you see differences in behaviour between different EMCA's?

           

          Regards,

          Rajath

          • 2. Re: Stop laptop providing VConn power?
            OlEr_1999891

            Hi Rajath!

             

            Thanks for getting back. We have tried with multiple cables so not sure that is the problem. Most likely our problem is somewhere else, just double check so to remove one possible cause.

             

            But the reason for some laptop starting VCONN, can that be changed by modifing some of the paramters in the PD-configuration file? When we use default Cypress configuration file for CCG4 host we don't see this behaviour, but when we reconfigure the SVIDs to become a docking station (DP sink) it starts to happen. Isn't continously powered VCONN only there for certain dongles that doesn't want to use VBUS for power or for active cables where the chip needs power all the time?

             

            Cheers

            Olof

            • 3. Re: Stop laptop providing VConn power?
              RajathB_01

              Resolution summary:

              The problem was cornered to signal integrity on the DP main link. The PS8742 output was too strong leading to over-equalization at the reciever. Finally Aux interception had to be disabled to get the pre-emphasis and swing to the lowest values. The EQ settings will have to be altered by changing the parameters in datamux_ctrl.c file.

               

              Regards,

              Rajath