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TUSB4020BI: TUSB4020BI：Operation of Bus Power

Takashi Hosokawa
Expert 1455 points
Part Number: TUSB4020BI

Hi All,

I have received questions from customers about Bus Power operation of TUSB4020BI.

When TUSB4020BI is operated with Bus Power, is there specification that permits / prohibits connection by USB Descryptor of connected to Downstream side?

For example, if bMaxPower of the device connected to the Downstream side is set to 100 mA or more, can the TUSB 4020 BI be connected as it is? Will not the connection be prohibited?

I saw the datasheet, but the contents could not be confirmed.

Best Regards,

Takashi

  • 0
    TI__Guru 60870 points
    Hello Ritsuo-san,

    In theory, each USB 2.0 port may only consume a maximum of 5V/ 500 mA of power during active operation. Also, a USB specification compliant bus-powered USB 2.0 hub would only supply 5V/ 100 mA to each downstream port.

    In reality, the power consumption of the USB ports is not enforced outside of overcurrent protection. Existing USB drivers do not check the descriptors for the listed max power and use that information to determine if a device can be enumerated or not. Essentially, if a USB device can be powered without invoking an overcurrent condition, the system will recognize it.

    Regards,
    JMMN
  • 0 in reply to JMMN
    Expert 1455 points

    Hi JMMN-san,

    Thank you for your quick response.

    I will contact the customer immediately.

    Takashi