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TUSB4020BPHPEVM: Can I use TUSB4020BI as bus-powered USB hub ?

Part Number: TUSB4020BPHPEVM
Other Parts Discussed in Thread: TUSB4020BI, , TPS2561

TUSB4020BI two-port USB 2.0 hub on design specifications.

In the data sheet, TUSB4020BI is recommended to be designed as a self-powered USB hub,
Can I use this as a bus-powered USB hub?

Below is the time when it was possible,
To design a bus-powered circuit based on the circuit diagram of TUSB4020BPHPEVM, is the change correct as follows?

· Remove the USB power switch TPS2561 because it does not use external power from the AC adapter.
· After supplying VBUS from the host side to the regulator etc., connect it directly to the connector on the device side.

If there are errors and caveats,
I would like to have some advice.

Best regards,

  • The TUSB4020B was designed as a self-powered hub. You can certainly have a bus-powered implementation, and you will have no functional issues, however the configuration descriptor on the device is fixed to advertise the device as self-powered, with no power consumption from Vbus (bMaxPower = 0); so you won't be able to get a USB compliance logo using that configuration.

    If you still decide to go with that configuration, your understanding is correct; you will still need some voltage regulators to get 3.3 and 1.1 V from Vbus (to power-up the TUSB4020B), and Vbus on the downstream ports could be directly connected to the Upstream's Vbus terminal.

    Regards,
    Jorge
  • Jorge,
    Thank you for your reply.

    I have a question about the following.

    >> however the power on from the device as self-powered, with no power consumption from Vbus (bMaxPower = 0);

    I do not understand the details about the configuration descriptor yet,
    Does that mean I need to rewrite the configuration using something?

    Also,
    As a situation to use, I am planning to use a hub between the USB camera and Raspberry Pi 2 or 3 (Iout = 1200 mA),
    so I am worried about power shortage to make it bus-powered.

    In EVM, TPS74801RGW (3.3 V) and TPS7A4533KTT (1.1 V) are used for the regulator,
    but do you think they will have sufficient power even if they are changed to a bus-powered ?

    Best regards,
    ichioka

  • Hello Ichioka,

    The USB hub descriptor cannot be changed, so the TUSB4020 will always reports as self-powered even if it is bus powered. Functionally, this is not an issue as long as the host can provide enough power, but it means that you would not be able to get a USB logo on your product since it doesn't follow the USB specification for a bus powered hub.

    You should be able to power the TUSB4020B from the Rasberry Pi, but I do have some concerns about if enough power will be available to the downstream ports of the TUSB4020B.

    Regards,
    JMMN