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Original question:

TUSB320: USB 2.0, USB 3 and BC 1.2 compatible source

TUSB320EVM: USB C Current Mode detection vs Thunderbolt

Matt Krolick54
Intellectual 400 points
Part Number: TUSB320EVM
Other Parts Discussed in Thread: TUSB320,

I am designing a device that requires the full 3A @ 5V from a USB C port. This device needs to check the current capability of the host to make sure that 3A is available before drawing power. I bought the TUSB320EVM to evaluate what current levels the ports on my laptop can provide in hopes that I can integrate the TUSB320 into my product. I have the EVM set up for UFP mode and GPIO mode (switch settings are 1=ON,2=ON,3=ON,4=OFF,5=OFF,6=OFF,7=OFF,8=ON and R10 has been removed to set GPIO mode). On the Dell XPS 19 9370 laptop that I have, all three USB C ports seem to only advertise 900mA (D1 lights up and D2 stays off). However two of these ports are 3A capable and are Thunderbolt capable as advertised by the lightning bolt symbol next to them and in the manual. I have tried to draw power from these ports using a DC load and I can't draw more than ~1.5A before the port detects an overload and turns off power. 

I understand that Thunderbolt is an alternate mode of USB C and presumably when I am in thunderbolt mode I can get the full 3A. However only 900mA is advertised (using the resistors on the CC1/CC2 lines and thus the output of the TUSB320EVM). Is it specified anywhere at all that if a device supports 3A in thunderbolt mode it should show that it can using the resistors on the CC pins? What kind of solution would you recommend for my application where I'd like to detect the maximum current capability of a port that might support thunderbolt mode? The device I am designing does not have a microcontroller so I'd like the port controller chipset to handle all the work.

Thanks,

  • 0
    TI__Mastermind 27925 points
    Hi Matt,

    I just wanted to let you know I am working on this issue. I'm going to look into some possible solutions, and I will follow up as soon as I'm done.



    Thanks,
  • 0
    TI__Mastermind 27925 points
    Matt,

    I used the TUSB320EVM with my Dell Latitude laptop and was unable to reproduce your issue. Could you please measure the voltage on the CC pin during operation and let me know what you see?



    Thanks,
  • 0 in reply to Nicholaus_Malone
    Intellectual 400 points
    Hi Nicholaus,

    I've also tried this on a Lenovo X280 with the same results. Again, D1 is on and D2 is off. Depending on cable orientation, CC1 is .900V and CC2 is 0V.
  • 0 in reply to Matt Krolick54
    TI__Mastermind 27925 points

    Hi Matt,

    Based on the information in the TUSB320 datasheet, a CC line of 900mV means that the port on the laptop is advertising 1.5A, which according to your measurement is what the port provides; however, 3A should be supported because the Dell XP 19 9370 user guide states it provides 3A, and you want to detect if you can get more power from the Thunderbolt alt mode.  Is that correct? 

    Also, can you confirm that the laptop model is a Dell XPS 19 9370.  I am searching for this user guide, but I can't find that model number.

  • 0 in reply to Nicholaus_Malone
    Intellectual 400 points

    Hi Nicholaus,

    Yes this is correct. The port advertises 1.5A but I want to get 3A. Sorry I mistyped the laptop model number. The laptop is a Dell XPS 13 9370. I notice the exact same behavior on a Lenovo X280.

    Is it normally the case that I need to get the port into Thunderbolt mode before I can get the full 3A? I have an HP ZBook Studio G4 laptop which has two Thunderbolt ports which advertise 3A no problem.

  • 0 in reply to Matt Krolick54
    TI__Mastermind 27925 points
    Matt,

    I only have a limited understanding of the Thunderbolt protocol, but I do know that both USB 3.1 and Thunderbolt 3 can utilize Power Delivery. The Power Delivery specification is separate from the USB or Thunderbolt specs. According to the information I have found on the Dell XPS 13 9370, all of the USB Type-C ports on your laptop support Power Delivery.

    This Power Delivery spec does not guarantee a certain amount of power, but only defines how the power delivered is negotiated. So, a port that supports Thunderbolt 3, USB 3.1, or Power Delivery does not guarantee that 3A of current will be available. The amount of power delivered is up to the discretion of the manufacturer, Dell. I have not been able to find this 3A via Power Delivery spec yet. Could you point me to where you see this?
  • 0 in reply to Nicholaus_Malone
    Intellectual 400 points

    Hi Nicholaus,

    The 3A number is probably an incorrect assumption on my part, as the Thunderbolt enabled devices (HP laptops) that I've had experience with are 3A capable. It seems unclear from reading datasheets or product specs the power capability of each port, so I've had to actually order laptops to test their capability. For devices that support USB PD, I'd like to negotiate as much power as possible. Is there a single chip solution out there that can do this or would I have to build my own?


    Thanks,

  • 0 in reply to Matt Krolick54
    TI__Mastermind 27925 points

    Matt,

    Yes there is!  The device you're looking for is a PD Controller, and we have a few.  For example, with the TPS65987D, you can negotiate up to 100W of power (the maximum for PD 3.0).  Again though, the manufacturer can choose not to allow that much.  They could only allow 1.5A, which is what seems to be the case for your Dell XPS 13.

    The only advice I can give you as to exactly how much power will be provided is to contact the manufacturer.