4 Replies Latest reply on Aug 1, 2013 1:35 PM by Kirk

    E6XX - LVDS Control signals

    Community Member

      Hello,

       

      For one of our design, we have made a board based on E6XX and EG20T chipset.

       

      Most of the manufactured boards (more than 95% out of 200 boards) works flawlessly and didn't required pull-up on LVDS_BKLTEN and LVDS_BKLTCTRL signals (GPIO_SUS1 and GPIO_SUS2 respectively) to turn on the LVDS backlight.

       

      However, some of the boards need those pull-up in order to always enable the backlight during the boot stage. If we power off the "defective" boards (without pull-up) and quickly power them on again (less than 10 seconds after power off), the LVDS issue disappear but if we wait more than 10 seconds we always observe the LVDS issue. The backlight is the only issue on the "defective" board. Their voltage rails, clocks and power sequence are good and we can access them through wifi, and use them without any problem.

       

      This issue seems not related to a power ramp-up time on boot because all the power rails are shut down in less than 50 ms after power off, so the board is always in the same state after 10 seconds or more. 

       

      The easiest trick we have found was to pull-up the GPIO_SUS1 and GPIO_SUS2 signals in order to force the backlight enable signals at startup. Have you ever experienced such an issue in your design ?


      Best regards,

        • Re: E6XX - LVDS Control signals
          FrankWeerdenbur Green Belt

          Hello Goobie,

           

          When you power down all power rails, what happens with VCC33RTC (pad M13)?

           

          My thought:

          In case VCC33RTC spike or drop then RTC clock not running properly, which might cause wrong reading op pull up straps.

           

          Best regards,

          Frank

            • Re: E6XX - LVDS Control signals
              Community Member

              Dear Frank,

              When we power down our product VCC33RTC is drive to ground. We don't use a RTC backup battery.
              VCC33RTC is directly connect to pin V3P3_RTC from DA6011 (DIALOG).

              At now we observe the issues below:
                - Some (10/3000) boards doesn't start proprely when we plug main batteries. In fact they start properly but the LCD backlight stay black.
                - They start properly when we
                   - 1 / change tunnel creek ( E620) or
                   - 2 / add a 10K pull-up to 3.3V on signal LVD_BKLT_PWM ( pad P1) and LVD_BKLT_EN (pad N4) or
                   - 3/  start the board with the ON/OFF button ( PWRBTN_B pad J11 DA6011)
                - the problem is reproducible

              Some questions:
                 1/ need signals  LVD_BKLT_PWM ( pad P1) and LVD_BKLT_EN (pad N4) a 10 K pull-up ?
                 2/ if yes what is the risk having this signal without pull-up ?
                 3/ If a product start properly today what appends later?
               

              Please fill free to contact me if you need more details. This issues are priority to us.

                • Re: E6XX - LVDS Control signals
                  FrankWeerdenbur Green Belt

                  Dear Goobie,

                   

                  Here at our company Eltan we have done customizations of Phoenix BIOS for a lot of TunnelCreek projects.

                  Maybe we are able to create special debug BIOS to detect difference of both GPIO_SUS signals and/or backlight behavior of the video BIOS between good and defective boards. Please contact us directly by email if you are interested.

                   

                  According to the datasheet both GPIO_SUS signals do not have strap functionality, so you are free to add pull ups without any problems. In case adding the pull ups will solve your problem, I recommend to implement also the pull ups on the other working boards for future precautions.

                   

                  I expect the root cause of your problem is that the RTC crystal requires 2 seconds to run properly after power up of VCC33RTC. You might confirm by measuring with low pF probe on RTC crystal signals. The initialization of the backlight by the video BIOS might be moved away from bad RTC clock time frame by adjusting the boot BIOS sequence.

                   

                  Best regards,

                  Frank

                  www.eltan.com 

                    • Re: E6XX - LVDS Control signals
                      Kirk Brown Belt

                      Hi,

                       

                      Backlight is a "sticky" subject.  If you are using panels with CCLF backlights *the ones that need the power inverters, it could be that the in-rush current for the power supply startup is too high for you power supply and by changing the timing a bit, will allow it to work or not.  You could try changing the T1- T5 timing for the panel sequencing to see if giving the backlight more or less time changes anything.  My guess is that putting pullups on those signals is manually changing the startup timing and that is what changes your sequence.

                       

                      Many panels are VERY touchy about their startup timing (Chi Mei aka CMI panels require very strict timing and MUST be operated in spec- others are more lax on their power sequencing timing in my experience).

                       

                      Alas, I am a graphics software person so I cannot speak to what the H/W ramifications of your signal pullups may be doing hardware-wise.

                       

                      Hope this helps.