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DS90UB947-Q1: During the thermal test, a black screen was found, and then we found that it was related to the temperature of 947.

chaoyi zhang
Prodigy 40 points
Part Number: DS90UB947-Q1

Hi , Ti colleague,

During the thermal test, a black screen was found, and then we found that it was related to the temperature of 947.
When heating the back area of the 947, a black screen will appear;
The backlight is black, but the power supply is stable;
I2C can't read opposite 948;
We went through the registers of 947;
The following two registers are different;
0x0a Register secondary screen is 0x06 when black, 0x04 when normal
0x5a Register secondary screen is 0x1d when black, 0xcd when normal

I am looking forward to your reply. Thank you very much!

  • 0
    TI__Mastermind 22340 points

    Hey Chaoyi,

    It looks like in good case you are running in dual FPD mode and in bad case you are running in single FPD mode port0.

    This seems like either a hardware issue or instable frequency or some sort of power-up sequence, but before we go there ... can you provide full register dump of good vs bad run of 947 and of 948 if possible please?

    1. What is your Pclk frequency for this application?
    2. What type of temp testing are you doing? How high temp, etc. ?
    3. Does black screen ever recover when you go back down to room temp or when it fails it never recovers?
    4. Does this system work once cooled down?
    5. How many systems were produced and how many systems is this issue happening on? 
    6. On your physical hardware, how many FPD-Link channels are connected between Ser and Des?

    Do you have scope capture of power-up sequence for 947 & 948? We need to ensure the rails/delays follow the recommended sequence on datasheet. Also, you do power-up the 948 after the 947 correct?

    947 power sequence

    948 power sequence 

    Regards,
    Fadi A.

  • 0
    Prodigy 120 points

    Hi Fadi

    We can see from the DS90UB947 specification sheet that Absolute Tjmax is 150 degrees and Tc is 105 degrees. So, what is Recommended Operating Tjmax? We have conducted high-temperature testing and found that the chip caused the screen to black out at 107 degrees.

    In addition, we found during testing in a temperature box with a high temperature of 85 degrees Celsius that the chip's rapid rise from room temperature of 25 degrees Celsius to around 65 degrees Celsius can also cause a black screen. How is this explained? Is it because the DS90UB947 cannot receive a sharp temperature rise?

  • 0 in reply to zenanding
    TI__Mastermind 22340 points

    Hi Zenanding,

    zenanding said:
    We can see from the DS90UB947 specification sheet that Absolute Tjmax is 150 degrees and Tc is 105 degrees. So, what is Recommended Operating Tjmax?

    For hot/cold temp testing you need to test the IC within the datasheet spec which is -40 C abs max cold temp and 105 C abs max hot temp. You need to stay within those upper and lower limits. 

    947 datasheet specifies the temp ramp ranges that the device can handle. 

    Also, please ensure to apply the script provided in the datasheet that's part of the power-up sequence.

    When you say black screen, what exactly is failing? Are you losing lock or is there a power-supply issue? What exactly is happening at the device level when the failure occurs? 

    Do you ever recover from the black screen or does it stay black screen until you power-cycle? 

    Can you provide a register dump of the Ser and Des at the point of failure ?

    Can you provide a scoep shot of your power supply rails and PDB we need to ensure your power-up sequence matches the datasheet recommendation. 

    Regards,
    Fadi A.