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TUSB8041: USB_VBUS specification and Vbus detect function details

Part Number: TUSB8041
Other Parts Discussed in Thread: TIDA-00288,

Hello,

I am implementing an on board USB3 hub on a board that we are designing using a TUSB8401 device and basing it on the TIDA-00288 4-Port USB 3.0 Hub Reference Design.

I have a quick question on the exact usage of the USB_VBUS pin i.e. pin 48 of the device. On the reference design this pin is connected to the Vdd bus of the USB3 connector. In an external hub design this USB_Vbus pin will get switched to +5V by the power controller on the host board. The datasheet says that a resistor divider must be used to keep this voltage within spec. However I cannot find any details on the exact function of this pin in the datasheet and if there is a max low and a min high voltage spec for the pin.

In the block diagram it just shows the pin going to a Vbus detect function. Can you tell me what the function of this Vbus detect block is please?

In my case I will not have any host power management IC (I am integrating the TUSB840 directly in the board so no requirement for power management IC). I will have a USB power enable signal available but this is only a 3.3V signal. This signal will be enabled by the USB host on initialization as the TUSB841 device will be permanently connected and thus USB enumeration should begin immediately on power up. (Is there an integrated ID resistor on the DP line in the TUSB8041 to kick off the enumeration process when conneced?) 

Should I adjust the resistor divider to produce the same voltage at pin 48 for a 3.3V I/P as opposed the Vbus 5V input. I hope my question is clear enough and thanks in advance for your help.

Best regards,

JB

  • Hello John,

    In an answer to your first question, the USB_VBUS pin is the power monitoring pin for the TUSB8041. The minimum and maximum values for voltage can be found on page 9, in section 7 of the datasheet for the TUSB8041.

    In your second question, the VBUS detect just determines if VBUS exists.

    In your power management question, you should be able to just keep VBUS high if you can guarantee that the host will be there. And yes, if you adjust the resistor network to be the same voltage for a 3.3V input, this should be fine.

    Best,
    Gerasimos
  • Gerasimos,

    Thanks very much for getting back.

    I think that I have enough info to proceed.

    Regarding on the spec for the USB_VBUS pin; as you say the voltage range for the USB_VBUS pin is specced in the absolute max ratings table but I was asking what the functional range was i.e. what minimum voltage is required on the pin before the device determines that USB VBUS is present and the same for max low voltage.

    Thanks again for your help.

    Best regards,

    JB.