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TPS65981: UFP/Source connection to tablets without battery

Oba
Genius 17405 points
Part Number: TPS65981


Hello,

My customer is designing a USB application with TPS65981 like the below.

 

The board has USB2.0 device IC and it is connected to a tablet through TPS65981 and Type-C connector.
And power is provided from this board. So this board acts as UFP and power Source with power role swap request.
It works well.

Then recently they found that this board have to also support tablets without battery.
Because this board is UFP, it can’t provide power without CC negotiation. So the tablet never power up in this case. 

Is there any good way to realize UFP/Source connection to tablets without battery??
This board doesn’t have MCU to control TPS65981. If adding MCU, can this be realized?

Regards,
Oba

  • 0
    TI__Mastermind 36756 points

    Hi Oba,

    The tablet should automatically present Rd in a dead battery case. This would allow the TPS65981 to source power to the tablet. If the Tablet is not presenting Rd on the CC line, then the TPS65981 cannot present VBUS.

    Thank you,
    Eric

  • 0 in reply to Eric Beljaars
    TI__Genius 17405 points

    Hello Eric,

     

    Thanks for your reply.
    So I feel that TPS65981 has to be configured as “Dual Role” to connect to tablets in dead-battery. Correct?
    In this case, TPS65981 becomes DFP/Source. Also even if tablets is not in dead-battery, I think TPS65981 could start as DFP/Source because of Dual Role configuration.
    So after providing power as DFP/Source, I think it has to be changed to UFP by role swap.

    Can it be realized with an additional MCU to control TPS65981?
    Is it possible to realize without MCU? 

    Regards,
    Oba

     

  • 0 in reply to Oba
    TI__Mastermind 36756 points

    Hi Oba,

    Yes, you should configure the TPS65981 to be a Dual Role Port in this use case. You should not need an MCU to enable this functionality. You can configure the Port Control register to meet your requirements. For example, if you select "Initiate Swap to Source" then the TPS65981 will send the PR Swap request to become the source. However, if you select "Process Swap to Source" Then the TPS65981 will not send the PR Swap request but it will accept it if the other device sends the PR Swap request.

    You should be able to use the Initiate/Process Swap bits to get the desired power/data roles for your application.

    Thank you,
    Eric

  • 0 in reply to Eric Beljaars
    TI__Genius 17405 points

    Hello Eric,

    The customer has confirmed it works well with Android tablets with Dual Role and both initiate/process Swap to Source and both Initiate/Process Swap to UFP.
    But it doesn't work with iPad pro. When connecting to dead-battery iPad pro, TPS65981 successfully start to provide VBUS power , but it doesn't change to UFP. It stays in DFP.

    Do you know why it doesn't work with iPad PRO?

    Regards,
    Oba

  • 0 in reply to Oba
    TI__Mastermind 36756 points

    Hi Oba,

    This could be something specific to the Ipad Pro rejecting a data role swap. I would suggest using a PD analyzer to take a PD trace to determine what is happening in the PD protocol.

    Thanks,
    Eric