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DRA76P: Wrong VOUT1 output

Francois Charlot
Mastermind 23947 points
Part Number: DRA76P

Hello,

The VOUT1 video output of my customer system worked properly in its version 01. They have made a 02 PCB revision and got an odd behavior, when VOUT1 is connected the same way in both board revisions.

In the 01 revision, vout1_clk is generated correctly from the pinmux tool-generated padconf.

In the 02 revision, the voltage level on vout1_clk is too low, making the video serializer failing to synchronize.

However, by changing the padconf definition from output to input in revision 02, there is an improvement as the image manages to display, but one may see that some pixels in parts of the image are incorrect.

Finally, the 02 display output becomes good after we reset the board through PORZ, but resetting through u-boot or at the OS console level does not improve the display.

Could you please help the customer fix this issue? Thank you.


Best regards,
François.

  • 0
    Expert 1060 points

    Hi Francois,

    Thanks for starting the thread. I am the HW developer of this system. I would like to add some more information:
    1- We have done the tests on 5 prototypes of version 02, all of them show the same wrong behavior.
    2- We have PORz connected to a switch, which when pressed manually, always completely solves the problem.

    Regards,

    Ale

  • 0 in reply to AClemotte
    TI__Mastermind 47962 points

    Hello Ale,

     How are you doing the initial power-up and reset?  Is PORz held low until well after the supplies are valid?  Can you measure that with an oscilloscope?  My primary suspicion is that you may not be getting a good power-on-reset during the initial boot.

    You mentioned in email that you added a 0 Ohm resistor on the clock.  Can you remove the resistor completely?  I just want to confirm that there is nothing else on the PCB that is affecting the signal.

    Can you provide the register value for the PADCONF register, read from the SoC (in both the passing and failing configuration).  

    For completeness, you answered a couple of other questions in email, pasting that here:

    1. Can you probe the vddshv2 rail?  Is it at a valid level?
      1. VDDSHV2 is powered with an exclusive regulator (Generic VIO B on Power_Regulators sheet). I have probe and its measure 1.799V, which is a valid level.
    1. Can you also probe other signals on the vout1 bus – are they switching rail to rail?
      1. Yes, they are switching rail to rail (1V8)

    Thanks,

    Kyle

  • 0 in reply to kcastille
    Expert 1060 points

    Hi Kyle,

    Your suspicion was right! In the PCB update we did not mount a resistor and the VDDSHV2 rail was not being included in the PORz chain. We have changed the assembly and the problem has been solved. Thank you!

    Regards,

  • 0 in reply to AClemotte
    TI__Mastermind 23947 points

    Hi Kyle and team,

    Fantastic job! Thank you very much!


    Best regards,
    François.