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TPS65982: Multiplexing LSX pins to SBU pins

Eric K.
Prodigy 70 points
Part Number: TPS65982

Hi,

According to Table 4, Figure 44, and section 9.3.4.3 in the TPS65982 datasheet the 1st stage digital crossbar multiplexer should allow the LSX_R2P and LSX_P2R to be routed to SBU1 and SBU2 respectively when "The connections are configurable via firmware." However, we have not been able to figure out how this is accomplished.

Please share how we can configure the digital crossbar multiplexer to make the SBU pins connect to the LSX pins.

When reading out the read-only Data Status Register 0x5F we are finding that the bit ForceLSX is 0. Would somehow setting ForceLSX to 1 allow us to route the multiplexer this way? If so, how can we make ForceLSX 1?

Best regards,

Eric

  • 0
    TI__Mastermind 36756 points

    Hi Eric,

    The SBU pins will automatically be multiplexed onto the LSX pins when the TPS65982 is in TBT mode and this muxing is required. It is not possible to force the multiplexer into this configuration. The TPS65982 will handle this automatically when TBT mode is entered.

    Thank you,
    Eric

  • 0 in reply to Eric Beljaars
    Prodigy 70 points

    Hi Eric,

    What is the best way to enter TBT mode when the TSP65982 is in APP mode?

    Would we set ThunderboltMode, bit 1 of register 0x52, to 1?

    Best regards,

    Eric

  • 0 in reply to Eric K.
    TI__Mastermind 36756 points

    Hi Eric,

    You would have to connect to another TBT device. Thunderbolt Mode is an alternate mode that both port partners need to support in order to enter the mode.

    Thank you,
    Eric

  • 0 in reply to Eric Beljaars
    Prodigy 70 points

    Hi Eric,

    Thank you for your reply. We do not plan to use our device for Thunderbolt, so we need some way to multiplex the LSX pins to the SBU pins without having to connect it to a Thunderbolt device.

    Could you please explain what the ForceLSX bit in Data Status Register 0x5F does? How can this bit be set to 1?

    Best regards,

    Eric

  • 0 in reply to Eric K.
    TI__Mastermind 36756 points

    Hi Eric,

    Unfortunately, the TPS65982 cannot multiplex the SBU pins onto the LSX pins without a Thunderbolt connection. The LSX bit in Data Status will only be updated when there is a TBT connection and the pins need to be multiplexed for the TBT controller.

    The LSX/SBU mux in TPS65982 only supports the Thunderbolt use case. Other applications for this mux cannot be supported with TPS65982.

    Thank you,
    Eric

  • 0 in reply to Eric Beljaars
    Prodigy 70 points

    Hi Eric,

    Okay, thank you for the insight.

    What was the best way you would recommend to be able to MUX the host's UART RX/TX out to a USB-C receptacle using the TPS65982 (without a Thunderbolt application)?

    Best regards,

    Eric

  • 0 in reply to Eric K.
    TI__Mastermind 36756 points

    Hi Eric,

    Unfortunately, the TPS65982 cannot be used to support such a custom multiplexing application. I would suggest using an external MUX instead to MUX those lines onto the SBU lines when your system requires it.

    Thank you,
    Eric

  • 0 in reply to Eric Beljaars
    Prodigy 70 points

    Hi Eric,

    Why does section 9.3.4.3 in the datasheet not specify that the 1st stage digital crossbar multiplexer does not configure the LSX pins to be MUXed out to the SBU pins unless the TPS65982 is in TBT mode and has a Thunderbolt device attached on the other end of the USB-?

    It seems this information would be quite relevant to designers who are looking to use the TPS65982. It may help some designers if this information is documented somewhere accessible.

    Best regards,

    Eric