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DS90UB926QSEVB: 926 GPIOs have a pulse output at power up

Andonis Wang
Prodigy 280 points
Part Number: DS90UB926QSEVB
Other Parts Discussed in Thread: TPS61165

Hi Team,

A customer used our DS90UB926 and a problem occurred. Upon power on DS90UB926, the GPIOs output a high voltage for approximate 2ms at 2V.  Because  one of the GPIOs is connected to the PWM/CTRL pin of the backlight control IC TPS61165, this leads to the flash of the display screen upon powering up. 

I have tested the output pins of 926EVM and found almost all the output pins have a high voltage pulse during power on, shown below,  channel 1 is PDB signal and channel 2 is the output pins of 926EVM.

        

This phenomenon happens on 928EVM too. So I wonder:

  1. Is it designed to work this way? And why?
  2. I have tested all the output pins, and only GPIO0 on 926EVM doesn’t have the pulse upon powering on. So I wonder does this happen randomly or it is designed to work this way. Can we guarantee this?
  3. Also I tried to pull down OSS_SEL and/or OEN before powering on 926EVM but this phenomenon still exists.
  4. How to solve this problem caused by the power up pulse of the 926 output?

Look forward to your reply. Thanks.

  • 0
    Mastermind 9165 points

    Hi Wang,

    I'm not sure that you have heard feedback from your colleague.
    But just let me share my case with you.

    I have seen similar (may be same) behavior on my customer board, yes, it was a problem for my customer, too.
    Unfortunately, this can happen with some FPD-Link devices. However, your colleague may have some workaround for this.

    Thanks,
    Ken





  • 0 in reply to Kenichiro
    TI__Prodigy 280 points

    Hi Ken,

    we have solved this issue. It is the wrongly powering up sequence that caused this problem.

    DS90UB926 has VDDIO and VDD input power supply. This issue occurred only because we powered up VDDIO and VDD at the same time.

    Powering up VDD and then powering up VDDIO can solve this issue.

    Thanks.

  • 0 in reply to Andonis Wang
    Mastermind 9165 points

    Hi Andonis,

    Happy New Year to You!

    Thank you for sharing your findings. This is good information.
    I think that the datasheet does not have enough information to explain this kind of behavior...

    Anyway, thank you and wish you a great 2017.

    Thanks,
    Ken