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TUSB546A-DCI: Unable to retrieve EDID data from monitor through AUX channel (TUSB546A-DCI)

DanS
Intellectual 390 points
Part Number: TUSB546A-DCI

Hi,

During booting, the processor is sending command through the AUX channel to retrieve the EDID data from the monitor but failed.
Looking at the DC bias of the SBU1(pin27) (see waveform) and AUXP(pin24) of the TUSB546A seems too low and may cause the failure.
Any advise on the low DC bias at the AUXP and SBU1 pin? Thanks. 
  • 0
    TI__Guru** 105235 points

    what is the data rate from processor though AUX channel?

  • 0 in reply to Brian Zhou
    TI__Guru*** 140195 points

    Hi,

    Are you referring to the 0.28V seen on AUXP/AUXN? If you look at the DP AUX bus block diagram as shown below,

    that common mode voltage is determined by the source (TX) itself. 

    Thanks

    David 

  • 0
    Intellectual 390 points

    Hi Brian,

    The data rate is 1Mbps.

  • 0 in reply to David (ASIC) Liu
    Intellectual 390 points

    Hi David,

    Any idea why the DC bias at pin27 (SBU1)  and pin24 (AUXP) is only 0.062Vdc since I am using a 100kohm resistor? Thanks. 

  • 0 in reply to DanS
    TI__Guru*** 140195 points

    Hi,

    On AUXP, you have a 100k strong pulldown. There should be a weak pullup to 3.3V (typical 1M). In the example of a strong 100k pulldown and weak 1M pullup, you will see ~0.3V. So 0.062V is a possible voltage depending on the weak pullup resistance on the sink side. 

    If you look at the common mode voltage requirement in the TUSB546 datasheet, you can 0.062V is within the spec.

    Are you connecting to a Type-C monitor? If this is the case, do you have a PD controller that controls the TUSB546?

    Thanks
    David

  • 0 in reply to David (ASIC) Liu
    Intellectual 390 points

    Hi David,

    Yes. I am connecting to a Type-C monitor. The TSUB546 is set to GPIO mode. The PD controller only controls the FLIP logic to the TSUB546.  

    I also tried connecting the TSUB546EVM to the Type-C monitor and is able to get 0.3Vdc bias at SBU1/AUXP pin. Does setting the USB-C port to DFP or UFP by the PD controller affects the DC biasing of the SBU channel from the monitor? Thanks.

  • 0 in reply to DanS
    TI__Guru*** 140195 points

    Hi,

    I would recommend letting the PD controller controls the TUSB546 CTL0 and CTL1 as the PD controller may set the TUSB546 into 2DP or 4 DP lanes depending on the PD controller CC negotiation with the Type-C monitor. 

    Does setting the USB-C port to DFP or UFP by the PD controller affects the DC biasing of the SBU channel from the monitor? 

    No, the DC bias is only controlled by the external pullup/pulldown on the AUX bus, when the TUSB546 is being configured into the DP mode.

    Thanks

    David