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TPS65981: OTG port on AM335x

Arnaud Van Genechten
Prodigy 90 points
Part Number: TPS65981

Hello,

I am currently designing a board with the TPS65981 and I wanted to know if this setup was possible before going further.

Here is how it should work: When first connecting a USB device (smartphone to be precise), TPS65981 negotiates a DFP data role contract. After enumeration by the AM335x processor, the VID and PID are checked. If they match a list of pre-determined IDs, the processor pulls-up a GPIO pin on TPS65981 to initiate a data role swap to become a UFP. When contract negotiation is over, a UFP/DFP GPIO event is triggered to change the state of the ID pin on the AM335x which then acts as a peripheral. It switches back to host when the device is unplugged.

Power role is always source.

Can I connect the usb_p and usb_n lines from the connector directly to the AM335x?

Can TPS65981 be powered only from PP_CABLE pin?

Thanks.

  • 0
    TI__Mastermind 36756 points
    Hi Arnaud,

    I believe this application would work correctly as you described it. However, I have a few comments on how it could potentially be simplified.
    If the AM335x is the I2C master to the TPS65981, you could easily send 4CC commands to do a data role swap after checking the VID and PID over I2C. This would eliminate the need to utilize complex GPIO events on the TPS65981. You could also set an I2C interrupt on the Data Status register to indicate to the AM335x that the negotiation is finished and to change the state of the ID pin on the AM335x.
    Also, I would recommend connecting the DP/DN lines through the TPS65981. All the TPS65981 does is mux the DP/DN lines to account for the cable flip.

    Thank you,
    Eric
  • 0 in reply to Eric Beljaars
    Prodigy 90 points
    Thanks for the answer. I have implemented all your suggestions. Can you confirm that TPS65981 can be powered only from PP_CABLE instead of VIN_3V3 and that all the LDOs will work?
  • 0 in reply to Arnaud Van Genechten
    TI__Mastermind 36756 points
    Hi Arnaud,

    The TPS65981 cannot be powered from PP_CABLE. The TPS65981 can be powered from either VIN_3V3 or from VBUS.

    Thank you,
    Eric