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TUSB321AI: USB-PD adapter in use. Is a CC chip for 5V 3A required or are pull-down resistors sufficient?

PowerMaster
Prodigy 90 points
Part Number: TUSB321AI
Other Parts Discussed in Thread: TUSB321

Dear Community

For a project we use a USB-PD adapter with our device in Upstream Facing Port (UFP) mode. So our device is a normal consumer of the USB power (e.g. 5V, 3A)


To get any energy out of a USB-PD adapter, a "hand shaking" on the CC pins of the USB type C port is needed. I discovered the TUSB321AI as a nice standalone solution, to get 5V and 3A from a USB-PD port. From several documentations I figured out, that the same result can be achieved with a pull down of the CC lines by two 5.1kOhm resistors to GND.


Can someone tells me, why there is the TUSB321AI chip for UFP mode, if the same can be achieved with two resistors? Am I wrong?


Thank you for your support.

Felix

  • 0
    TI__Genius 16150 points
    Hi Felix,

    Theoretically, this is possible. Placing pull-down resistors at CC pins for detection in UFP mode as long as your system does not exceed the low current level (500mA). Whether your system exceeds this level (mid current 1.5A or high current 3A), you will need 3 comparators to detect every current level to avoid overcurrent state. This is the reason that TUSB321 is recommended for this kind of application.

    Best Regards,
    Luis Omar Moran
    High Speed Interface
    SWAT Team
  • 0 in reply to Luis Omar Moran
    Prodigy 90 points

    Hi Luis

    Actually your answer is super fine.

    But I tested it and connected only 5.1kOhm resistors to the CC-lines of an 5V 3A USB-PD adapter. I connected this adapter to a 1.7 Ohm power resistor. See the result:

    I do not have many different USB-PD power suppliers to test. But in this case I received high current (3A) only via resistors. Is this normal?

    Thank you for your answer.

    Felix

  • 0 in reply to PowerMaster
    TI__Genius 16150 points

    Hi Felix,

    You are right, in this case when you connect an adapter of 5V @3A, it works. Although, if you connect another adapter below of 3A, your system won't be able to adapt the circuitry at this new level current. As well, this system won't be certified, due your system should be detect the 3 different levels of current in case you want to certify your system. Otherwise, if your system always you have the certain that an adapter of 3A is connected, it works but it can't be compliant with another current levels.

    Best Regards,

    Luis Omar Moran

    High Speed Interface

    SWAT Team 

  • 0 in reply to Luis Omar Moran
    Prodigy 90 points

    Hi Luis

    This is super clear.
    Thank you very much for your support.

    Best regards
    Felix