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TPS65981: USB Power Delivery and Type C questions

max poe
Prodigy 30 points

Part Number: TPS65981
Other Parts Discussed in Thread: TPS65982, , TPS65983B, TPS65987D

Hi all, I have a few questions about USB Type C Power delivery and role swap functionality. I have an application where I need to network together a number of mobile tablets with USB Type C connectors into a LAN, but also provide charge to them. For this I have already chosen a USB Ethernet peripheral IC but the application demands that the tablets remain charged while in use.

As I understand, USB Type C does initial negotiation (determining type of cable, orientation, etc) via a ~5K pullup or pulldown on one of the CC lines, in the cable itself. This will configure the tablet to either operate as a Host (DFP) and provide power, or as a peripheral device (UFP) and consume power. Is this correct? If so, then neither case is desired since the tablets require charging and acting as a host to a peripheral concurrently. Since I am looking to power the USB Type-C tablets and establish a connection to a USB 2.0 peripheral, I would need use the remaining CC pin and an active IC on the other end to perform a "role swap" Is this correct? I suppose I could either use a cable designed to put the tablet in Peripheral mode and perform an active data role swap, or use an "OTG" cable and perform a power delivery swap. Is this correct? Just to make sure, it would not be compliant to simply connect the peripheral to the tablet and force 5V onto the power lines, correct? This of course would be the simplest but I fear it is not allowed and may even risk damage to the tablet.

What is the simplest viable solution to ensure the necessary functionality? Is active circuitry really required or am I missing something? It appears both the TPS65981, TPS65982, and TPS65983B ICs are suitable but I do not quite know what the differences are between these IC's, so guidance here would be greatly appreciated here.

 TL;DR questions:

  • Is "role swap" necessary for tablet to operate in Host mode whilst consuming power?
  • Is an active IC nessesary to implement role swap if it is not possible to use passive components?
  • What is the difference between TPS65981, TPS65982, and TPS65983B?
    • Do these chips support USB2.0 passthrough to a peripheral device?

  • 0
    TI__Mastermind 36756 points

    Hi Max,

    • Is "role swap" necessary for a tablet to operate in Host mode whilst consuming power?
      • Default USB Type-C connections are DFP/Source or UFP/Sink. If the tablet needs to be the DFP/Sink, then it is required to support PD as either a Power role Swap or Data Role Swap will be required to get into the desired power/data role. 
    • Is an active IC necessary to implement role swap if it is not possible to use passive components?
      • Yes, a PD controller would be required to manage the Power/Data Role swaps.
    • What is the difference between TPS65981, TPS65982, and TPS65983B?
      • Do these chips support USB2.0 passthrough to a peripheral device?
        • TPS65981 is in an Industrial QFN package while TPS65982 is in a BGA package. The TPS65983B is only supported for TBT device designs following an Intel reference design. I would suggest looking at the TPS65987D for your application as it appears you do not need the USB2.0 passive mux in the TPS65982. If you are using the TPS65987D, you can simply short the D+/D- lines on the Type-C connector and pass the USB2.0 signals to your peripheral device.

    Thank you,
    Eric

  • 0 in reply to Eric Beljaars
    Prodigy 30 points

    Thank you for your helpful reply!

    As I understand, I would need to use a PD compliant USB Type-C to Type-C cable, correct and cannot use the more robust type B (square) connector. Correct?

    Eric Beljaars said:
    I would suggest looking at the TPS65987D for your application as it appears you do not need the USB2.0 passive mux in the TPS65982. If you are using the TPS65987D, you can simply short the D+/D- lines on the Type-C connector and pass the USB2.0 signals to your peripheral device.

    Cool! I am taking a look at it now. Can you elaborate on what you mean by shorting the D+/D- lines? I know they are sometimes shorted together in "dumb" chargers to allow devices with Mirco-B connectors to charge faster (and other times analog voltages are asserted on said lines) but I would need to be connected to my USB peripheral. Do you mean to just connect them directly to the Ethernet peripheral? Thank you!

    Additionally, I notice the TPS65987D has SDA and SCL. I assume the registers are non-volatile and can be programed/configured without an additional MCU to set the registers to appropriate values on powerup? Thanks!

  • 0 in reply to max poe
    TI__Mastermind 36756 points

    Hi Max,

    Yes, a USB Type-C connector and USB Type-C to Type-C cable are required for PD communication. 

    What I mean by shorting the D+/D- lines is there are two pairs of D+/D- on the USB Type-C connector. Since USB2.0 is low-speed, you can short the D+ from one pair to the D+ from the second pair and do the same for the D- lines. This can be done at the Type-C connector to minimize any stub on the USB2.0 lines. You can refer to the TPS65987EVM for an example of this connection. 

    The TPS65987D needs an SPI Flash if there is no MCU present in the system. This is the same for the TPS65981 and TPS65982. You can use the TPS6598x Application Customization Tool to create your configuration file and export the Full-Flash binary image that you will load onto the SPI Flash. When the TPS65987D boots up, it will load the configuration and patch from the SPI Flash into its RAM. Again, the TPS65987EVM is a good example of how this hardware connection looks. 

    I hope this helps.

    Thank you,
    Eric