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TUSB546EVM: Default current limit

Thomas
Prodigy 10 points
Part Number: TUSB546EVM
Other Parts Discussed in Thread: TPS65982

Hello TI support,

 

I have a question regarding to the evaluation Board TUSB546EVM. We have a fixed setup where we want to connect a touchscreen to a PC through the evaluation Board.

 

Our Setup:

  • Touchdisplay
    • USB Type-C: Power (5V/2A), display and touch signals
  • PC
    • USB3.1 Type A
    • Displayport

    We tried the delivered EVM jumper configuration and the jumper configuration shown in the EVM manual. In each configuration the Power LED of the touchscreen lights up shortly and then switches off. I measured VBUS on the USB Type-C connection and noticed a toggling between 5V and 0V. The voltage of the USB Type-B connected is stable at 5V.

    I have tested following:

    • The touchscreen works with a direct USB Type-C connection from a standard laptop.
    • Even if the touchscreen is only powered with 5V via a USB charger, at least the starting screen of the touchscreen appears.
    • An USB flash drive connected to the TUSB546EVM works and it accessible through the PC.

    It seems that the voltage from the USB Type-B is not being forwarded by the TPS65982 chip. Does the EVM board have a standard current limiter below 2A or is the problem caused by a different reason?

    Thank you for your help

    • 0
      TI__Genius 9885 points

      Hi Thomas,

      Are you configured for 4 lane DP or 2 lane DP with 2 lane USB? You can probe the FLIP, CTL0, and CTL1 to determine this.

      If you are using 4 lane DP, you would need to supply wall power to the EVM.

      Are you also able to probe the CC1 an CC2 pins? A waveform of these pins before, and at the touchscreen attachment would be helpful.

      Best,

      Shane

    • 0 in reply to Shane Hauser
      Prodigy 10 points

      Hello Shane,

      i measured following:

      Only USB Type-B connected --- same as --- USB Type-B and Displayport connected

      • CTL1/EN - Low - 116mV
      • CTL0/AMSEL - Low - 2mV
      • Flip/Pol - Low - 140mV
      • CC1 - toggle - see image
      • CC2 - toggle - see image

      USB Type-B, Displayport and Touchscreen connected:

      • CTL1/EN - Low - 116mV
      • CTL0/AMSEL - toggle - see image
      • Flip/Pol - Low - 140mV
      • CC1 - toggle - see image
      • CC2 - toggle - see image

         

      AMSEL with touchscreen

      Best regards

    • 0 in reply to Thomas
      TI__Genius 9885 points

      Hi Thomas,

      Let me look into whether the PD controller limits the power delivery from the Type-B VBUS to the Type-C VBUS.

      Could you share which revision of this EVM you're working with? Its should be in the top corner of the board.

      Best,

      Shane

    • 0 in reply to Shane Hauser
      Prodigy 10 points

      Hello Shane,

      the PCB has following revision: INT017 REV_A2

      Best regards,

      Thomas

    • 0 in reply to Thomas
      TI__Genius 9885 points

      Thanks Thomas,

      I was able to recreate the setup in the lab and saw the behavior you described. From my test, I believe the PD controller is configured to limit VBUS to around 1.3A before it cuts off entirely. The source of this is likely that our EVMs firmware is using a low ILIMPP5V setting, described in the TPS65982 datasheet.

      From what I can gather, the reason our board limits current to this value is that the type-B upstream VBUS will only support up to 900mA of current. Since we wanted the board to be primarily bus powered, the intended use is for power draw around this value. The wall power socket gives the option to go a bit higher than 900mA for DisplayPort applications, however it seems we cannot reach the 2A you would require with the default firmware.

      You would need to generate your own firmware file for the PD controller if you want to pass more than ~1.3A. There is a configuration tool on the TPS65982 TI.com page that can be used for this purpose.

      Once you've created the config file, you can use the SPI programming header on the 546EVM to load this file to the memory chip.

      I hope this helps, let me know if you have any questions.

      Best,

      Shane