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Original question:

DS90UH948-Q1: Pairing with UB947

DS90UH947-Q1: Power up waveform issue

James Zhan
Expert 4365 points
Part Number: DS90UH947-Q1


Hi team,

My customer is using UB947 for the head unit application.

When they start up the UB947 with the UB948 board connected, they VCC1.1 have a step during startup..

But if unplugged the UB948 board, there is no step on the startup.

Could you help to check if any advices?

Thanks.

  • 0
    TI__Guru** 103215 points

    Hello James,

    This is most likely due to leakage through the 947 DOUT pins which are connected to the 948. When the 948 is powered on, the RIN pins will start toggling to send the back channel to the 947 so there will be some voltage present at the unpowered 947 DOUT pins. It is generally recommended to power the SER side first, followed by the DES side which also gives a more deterministic linking process with the adaptive equalizer 

    Best Regards,

    Casey 

  • 0 in reply to Casey McCrea
    TI__Expert 4365 points

    Hi Casey,

    My customer only do the head unit side and they could not know when will the display side will power up(Another Tier1).

    So it's hard for them to know the exact power up time..

    Does this waveform has any potential risk?

    Thanks.

  • 0 in reply to James Zhan
    TI__Guru** 103215 points

    Hello James,

    Please post the full power up sequence waveform including the VDD18/VDDIO, and PDB rails for review 

    Thanks,

    Casey 

  • 0 in reply to Casey McCrea
    TI__Expert 4365 points

    Hi Casey,

    Pls check the waveform as below.

    As mentioned, the display board is from another Tier1, so they couldn't know when will it power up.

    Are we seeing any risk for the step of VCC1V1?

    Thanks.

  • 0 in reply to James Zhan
    TI__Guru** 103215 points

    Hello James,

    Any deviation from the datasheet recommended power sequence is considered a risk and we should investigate how to address it. For the power sequence, I'm not sure I understand your 4 pictures. What is the difference between them? Also where is the PDB signal?

    Best Regards,

    Casey