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TPS65988: DRP and DRD on the same port not working

Bahar Bülbül
Prodigy 30 points
Part Number: TPS65988

Tool/software:

Hello Team,

We are currently developing a device on which we use TPS65988.

Our configuration will be as the following:

  • port A as sink and source (sink at 20V@3A, source 5V only), dual role data
  • port B as source only (5V), host only

Use Case 1:   The device is powered from VBUS only, port A sinks, port B sources

Use Case 2: The device is powered externally, both port A and B sources

So our device has 2 ways of powering:

  • Through external 24V
  • Through USB power delivery

The problem is, when the device is externally powered from 24V, the DRD mode on port A doesn't work in Host mode. I am curious if can this be happening because TPS sees the external 24V on the PP_HV pin? When we remove the 24V connection, we see the Host mode working without problems. However, this then disables the ability of device to be powered from USB.

Could you help me on this?Let me know if you need any more details. Thanks in advance!

Bahar

  • 0
    TI__Mastermind 37855 points

    Hi Bahar,

    When you say "Host mode", are you referring to that port acting in the DFP Data role?

    If yes, check the port control register for portA to make sure it can support "process swap to DFP".

    Why is 24-V being applied directly to the PPHV pins? Could you share a block diagram or schematic of the PD controller in your system?

    Thanks and Regards,

    Chris

  • 0 in reply to Christopher Lim1
    Prodigy 30 points

    Hi Chris,

    Yes I am referring to the DFP.

    Sure I could send you the schematic, but can I send you with private message?

    Thanks and regards,

    Bahar

  • 0 in reply to Bahar Bülbül
    TI__Mastermind 37855 points

    Hi Bahar,

    Yes, I sent you a friend request, you can share the schematic there.

    Are you able to successfully source 5-V? I think the 24-V on PPHV may be the issue.

    Thanks and Regards,

    Chris

  • 0 in reply to Christopher Lim1
    TI__Mastermind 37855 points

    Hi Bahar,

    Could you obtain a PD log of both ports during this failure behavior?

    Why is there 24-V on the PPHV bus?

    If there is a constant 24-V on the VUSB_IN, how are you expecting PPHV1 to source 5-V. It seems like the 24-V will always be present and the port won't be able to source properly.

    Thanks and Regards,

    Chris

  • 0 in reply to Christopher Lim1
    Prodigy 30 points

    Hi Chris,

    I shared you my schematic via PM. Would appreciate if you can have a look.

    Christopher Lim1 said:
    If there is a constant 24-V on the VUSB_IN, how are you expecting PPHV1 to source 5-V. It seems like the 24-V will always be present and the port won't be able to source properly.

    I understand your point, I will fix that. But how does this effect the DFP Data role?

    Thanks and regards,

    Bahar

  • 0 in reply to Bahar Bülbül
    TI__Mastermind 37855 points

    Hi Bahar,

    Yeah, I received the schematics. The most recent feedback to that into mind.

    Bahar Bülbül said:
    Christopher Lim1 said:
    If there is a constant 24-V on the VUSB_IN, how are you expecting PPHV1 to source 5-V. It seems like the 24-V will always be present and the port won't be able to source properly.

    I understand your point, I will fix that. But how does this effect the DFP Data role?

    Upon initial connection, a port (in this case port A) can enter as Power Source, Data DFP, or Power Sink, Data UFP. DFP is the same as host. In order for a Power Source, DFP connection, the port needs to be able to provide a 5-V source contract to get the initial connection. When sourcing, the PD controller expects to provide a 5-V contract, and will not complete negotiation if it does not see VBUS go to 5-V. On start up, the PD controller negotiates 5-V, then will close the PPHV->VBUS power path expecting 5-V on PPHV. 

    I'm thinking that when you leave the 24-V bus on, it leaves PPHV at 24-V and we can never complete the PD contract, and never become a DFP. When you remove it, the +5V bus that goes through D5 applies 5-V to PPHV, and the negotiation completes successfully.

    Thanks and Regards,

    Chris