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DS90UB948-Q1: What causes Lock signal down to 300us?

Chris Sha
Prodigy 235 points
Part Number: DS90UB948-Q1

Dear all, 

This is Chris. Recently my customer is testing ESD with our DS90UB948-Q1.

The customer is making a dashboard for SAIC and I hope you can give me some kindly help on it.

When they tested ESD of the product, they found that the dashboard screen will shake.

Below is how they test ESD of the product according to fig.1 :

  • The product is placed on a section of the copper strip and the metal frame of the product is connected to the copper tape.
  • The copper strip is divided into three discharge islands according to the distance, just as three circle.
  • The customer hits a voltage of 4kV on the middle discharge island and test the screen for abnormalities.

When testing the ESD, the DS90UB948-Q1's lock pin may drop down for 320us, just as below.

According to above test, I hope you can give me some suggestion on it. Or can you tell some possible reasons leading the phenomenon.

Thanks and best regards!

Chris

  • 0
    TI__Mastermind 19720 points

    Hi Chris,

    Is this for air discharge or contact discharge? Can you send me your schematic for both the 948 and the SER? Can you mark in the picture where you are doing the ESD strikes?

    Regards,

    Michael W.

  • 0
    TI__Mastermind 19720 points

    Hi Chris,

    Is this for air discharge or contact discharge? Can you send me your schematic for both the 948 and the SER? Can you mark in the picture where you are doing the ESD strikes?

    Regards,

    Michael W.

  • 0 in reply to Michael.Walker
    TI__Prodigy 235 points

    Hi Micheal, I have shared some material on webex.

    I need to compensate for the information, I hope you can confirm.

    It is for connect discharge.

    When the lock signal drops down, by testing the register of UB948-Q1, it seems that 0x1C will change from 0x3B to 0x33. I cannot confirm whether I2S  has some influence. It is noted that I2S pin is connected with GND.

    When the lock signal drops down, the power supply will drop down, too. But the customer thinks that the time of power supply dropping down is only 100us, less than lock signal (320us). 

    When UB948-Q1 works on pattern generation mode without UB941-Q1, the screen will not shake.

    Pls give some feedback on why the lock drop down so long today. And if there are any other reasons, pls share them with me.  

    Chris 

  • 0 in reply to Chris Sha
    TI__Mastermind 19720 points

    Hi Chris,

    Wait, the power supply for the 948 or the 941 is dropping? if any power supply drops this would cause our part to lose lock. Also when the power supply is brought back up the 948 will take some time to relock on to the signal. 220us sounds like the amount of time the 948 would take to relock onto the signal. 

    Find the root cause to the power supply drooping to fix your system.

    Regards,

    Michael W.

  • 0 in reply to Michael.Walker
    TI__Prodigy 235 points

    Hi Michael,

    But why patgen mode would not lead the screen shaking since their power supply also dropped down?

    And if any other possible reasons causing 948 unlocked?

    Can you confirm whether I2S has influence on it?

    Chris

  • 0 in reply to Michael.Walker
    TI__Prodigy 235 points

    Hi Michael,

    On the other hand, the customer tested the power supply and the drop time of power supply is only 10-100us. I think it is less than Lock drop-down time.

    Can you give the actual phase lock time test data?

    Best Regards!

    Chris

  • 0 in reply to Chris Sha
    TI__Mastermind 19720 points

    Hi Chris,

    What power supply is dropping is it a supply for the SER or the 948? What pattern generator are you using, the pattern generator on the 948 or the pattern generator on the SER? 

    The I2S will not cause the lock to drop.