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TPS65981: DisplayPort USB-C alternate mode questions - intermittent display output

Kenneth Mayer
Prodigy 50 points
Part Number: TPS65981

Hello everyone

I'm using a TPS65981 and TUSB1046 system as a DisplayPort alternate mode source, and I'm experiencing an unusual issue. I am able to get some output video on my monitor, but it plays for about 5 or so seconds, then the monitor enters sleep mode, saying that there is no DisplayPort signal, then wakes up for another 5 or so seconds half a minute or so later. There is of course some possibility that the issue lies in the native DisplayPort source, but I did not experience the problem in a very similar setup (nearly identical), that output through a native DisplayPort connector without any intervening hardware.

I think the problem might be caused by one of these elements:

  • Our TPS65981 was setup as a USB sink when it was designed and cannot source power. To fix this, we are driving 5V onto the USB-C connector through a bench top power supply. It is giving me some error interrupts (device incompatible and power-related issues).
  • Our TUSB1046 was setup primarily for 2 DP lanes + 1 USB SS pair, but I am using a USB-C hub with a DisplayPort output that supports only pin configuration C. I know that operating with only 1 or 2 lanes is required part of the DisplayPort spec, but I wonder if there could be some issue with the TUSB, since the 2 lower DispayPort lane input connections are floating and pin configuraton C specifies 4 DP lanes.
  • For simplicity, I have fixed the CTL1 and CTL0 inputs on the TUSB to 1 and 0 respectively (4/0 DP/USB with or without flip).

Is there anything in this setup that might be preventing the DisplayPort from working reliably?

Thanks!

  • 0
    TI__Mastermind 29545 points

    Hello 

    I've assigned this ticket to the relevant expert who will respond to you soon

  • 0
    TI__Genius 12700 points

    Hi Kenneth,

    I believe your configurations may be the issue. 

    I would recommend reflashing the TPS65981 with the appropriate DP settings that you need to match with the TUSB1046 and if you need source capabilities for your application you can configure it as a DRP. You may be getting some errors if the PD Controller doesn't have power on VIN_3V3 causing it to power up in dead-battery mode which could load default configurations instead of your project settings.

    I would also recommend using a PD Analyzer to debug the PD controller communications. 

    You can find a detailed process of the DisplayPort mode in Section 4 of the application note, with TUSB1046 example settings in Section 3.1. Once you verify the configurations match up with the Mux and the PD controller, you could also take a look at the Debugging Section 6.


    Once you have the reliable power supply on the PD controller and the TUSB1046 DP settings aligned I think it will resolve this issue.

    Thank you,

    Hari

  • 0 in reply to Hari Patel1
    Prodigy 50 points

    Thank you for your response.

    I don't believe that there is an issue with my configuration. My application is able to read the configuration/status registers from the TPS65981 during operation, and almost all of them look normal. The only unusual results come from the interrupt register, which reports Error_PowerEventOccurred and Error_DeviceIncompatible when the power supply is switched on. These two events are reported in byte 5, bits 0 and 3 in the IntEvent register on the TPS65981. This does point toward an issue with the power setup, but the fact that I do get a correct display output intermittently at least indicates that the system is at least partially functional from end-to-end.

    I should have been more specific about the configuration of the TPS65981. The problem is that it was designed to source power to the rest of our board, and so our board provides no power supply to its VBUS or PP_xxx pins. I have been able to configure it as a downstream-facing USB and DP port, but unfortunately, an external power supply connected directly to the USB-C breakout terminal was needed to supply a VBUS. This power supply, naturally, is not under the control of the TPS and only provides a fixed 5V.

    However, the 3.3V power pin is being supplied by an onboard source, and should be operating normally. It's just the VBUS and PP pins that aren't.

    I have followed the application note, and I do believe that I have configured the TUSB controls correctly. However, I am not entirely sure which GPIO events I should use. The application note assumes a slightly different PD controller that has different events available, that the TPS65981 doesn't seem to support. However, for my prototype, I am only using the TUSB in a single mode - 4 DP lanes, with CTL1 = 1 and CTL0 = 0, while the FLIP bit GPIO is mapped to the event "Port Connected CC2 (Cable Orientation Event)". The GPIO connected to CTL1 is just set high with no event and the GPIO connected to CTL0 is set low with no event. It might be helpful if you can tell me which events for the TPS65981 correspond to "Port 0 DP Mode Select Event", "Port 0 Cable Orientation Event" and "Port 0 USB3 Event" in Figure 2 of the alternate app note.

    Thanks for the help!

  • 0 in reply to Kenneth Mayer
    TI__Genius 12700 points

    Hi Kenneth,

    I do not recommend connecting a power supply directly to VBUS if that's what you're referring to. It's recommend to connect the PP_5V to a 5V source as this is the input to power VBUS and PP_HV is the input for the high voltage path. However, if you will be configuring the PD controller to be strictly just a sink then you do not need the external supply since the device on the other end should be sourcing a constant 5V contract to the PD controller via VBUS. You just need to have the configurations programmed on the Flash and the ADC pins setup accordingly. 

    As for the GPIO events, the events are labeled: "Port Connected CC2 (Cable Orientation Event)", "DP Mode Selection Event" and "USB3 Event."

    Thank you,

    Hari