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TPS65981: tps65981

martin bugge
Prodigy 180 points
Part Number: TPS65981

Hi

We have a design with a tps65981.

It is configured as Dual Power role. Portinfo 0x28 is 101b Source/Sink. Power Role = Source. Data Role = DFP. PR_Swap supported. DR_Swap supported

We are trying to collect cable information.

When connected as a power source I can find the cable information in register "Cable Discover Identity response (0x49)"

However, when we become power-sink, for instance connected to some docking stations which insist on being source there is no cable information present in register 0x49.

I assume that is by design since it is the source's duty to collect cable-information (USB Power Delivery WG Chair 4.4 Cable type detection).

I thought I could get the information by sending a SOP' Discover Identity using the VDMs command and get the reply from register 0x4F RX VDM.

But when the tps659891 is power-sink it seems to ignore the Discover Identity reply from the Cable.

I attach two images:

CRC-ok-from-tps65981-as-power-source.jpg: when the tps65981 is power-source it "reply" with GoodCrc and the information is found in 0x4F.

No-CRC-ok-from-tps65981-as-power-sink.jpg: when the tps65981 is power-sinke it do NOT "reply" with GoodCrc and there is no information found in 0x4F.

Is there a way to get the cable discover identity when the tps65981 is sink ?

Best regards,

Martin Bugge

  • 0 in reply to martin bugge
    TI__Mastermind 30000 points

    Hello,

    I've assigned this issue to the relevant expert who will get back to you shortly

  • 0
    TI__Mastermind 29755 points

    Hi Martin,

    What information are you looking for when in sink? Can you not find that when connected as source?

    Can you not connect the cable to other sink partner so you can retrieve the information?

    You are right when connected as sink, the information will not be available since the source will provide the power and collect the information.

    regards,

    Peter

  • 0 in reply to pdjuandi
    Prodigy 10 points

    Hi Peter,

    Question 1) What information are you looking for when in sink? Can you not find that when connected as source?
    Answer 1:
    we are primarily looking for the PID and VID of the active USB-C cable connecting the sink to the source.

    It would also be beneficial to read out the other information stored in the e-marker, but if it is a known PID/VID combination we can know the capabilities of the active cable.

    Question 2) Can you not connect the cable to other sink partner so you can retrieve the information?

    Answer 2:
    We do not control which active cable the user chooses to connect to our tps65981 USB-C DP alt mode monitor product, and we do not control what kind of 3rd party product the user connects to the other end of the active USB cable.

    Typically, if the user chooses to connect a self powered USB dock/hub with Power Delivery, this dock will be DFP (PD source) only. Our tps65981 device is therefore forced into sink from the start, even if our USB-C monitor product also is a typical DFP (PD source) device for all applications.

    If both the monitor and the dock enforces DFP at the same time, will it not cause a failure?

  • 0 in reply to Oystein Damhaug
    TI__Mastermind 29755 points

    Hi Oystein,

    Ok, thanks for the clarification.

    For USB PD2 device like TPS65981, an UFP can't talk to the cable but a DFP can by issuing the 4CC "AMDs" - Start discovery process command.

    So even though PD is sink, you can change role to DFP after PD contract and issue the AMDs command to get the cable information.

    Regards,

    Peter