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TUSB2046B: Recognition is intermittently cut off when 4 USB devices are connected

Taesung Lim
Prodigy 10 points
Part Number: TUSB2046B

I made a USB hub device using the TUSB2046B.

However, the device works normally when three USB devices are connected, but when the fourth device is connected, all connected devices are disconnected and reconnected again and again.

The devices we connected are all 4 keyboards, under USB 2.0, and the speed is Full-Speed.

first equipment

second equipment

The 3rd and 4th devices connect 2 keyboards of the same model

  • 0
    TI__Guru 60865 points

    Is the hub set up as bus powered?  For USB 2.0 hubs, there are two components to making sure a bus powered hub is functional:

    1. Confirming that there is enough current from the upstream port to power the hub and the downstream devices without any drooping on VBUS (<4.5V)

    2. Meeting the USB 2.0 max current requirements of 500 mA per port.  If the max power consumption reported in the USB descriptors from the hub and the devices is greater than 500 mA, new devices may not enumerate properly, and resets may occur.  See the demanded current entry in the attachments sent, if those add up to greater than 500 mA that will be an issue even if the upstream port on the host can provide enough power.

    Regards,

    JMMN

  • 0 in reply to JMMN
    Prodigy 10 points

    It has been confirmed that the 5V input is normally applied to the power of each device.

    If you connect the connected downstream devices one by one and check the voltage and current, it normally operates by receiving input within 5V and 500mA without any abnormality.

    Connecting only 3 devices doesn't cause problems, but connecting a 4th device causes problems.

    This problem does not occur when only a specific device is connected, but occurs when the fourth device is connected even if connected in an arbitrary order.

    Could this kind of problem occur if the data transmission bandwidth is exceeded?

  • 0 in reply to Taesung Lim
    TI__Guru 60865 points

    Is the hub set to BUS POWERED mode?  If so, can you try setting it to SELF POWERED?  If it is in BUS POWERED mode it does NOT matter if there is enough power in the system, if the reported values add up to greater than 500 mA the host will not enumerate the fourth device properly.

    Regards,

    JMMN

  • 0 in reply to JMMN
    Prodigy 10 points

    As a result of checking through the oscilloscope, it was confirmed that it is in self-power mode. Also, when connecting 4 USB ports that can receive input from the TUSB2046, each device is a Full-Speed device. When the problem occurs.

    However, if 3 Full-Speed devices are connected and the last 4th device is Low-Speed or High-Speed, the problem does not occur.

    I'm just wondering if it's an issue related to the speed of the USB, but I can't find a clear cause.

  • 0 in reply to Taesung Lim
    TI__Guru 60865 points

    Can you share the schematic around the TUSB2046B?  What OS / driver is running on the USB host?  This could be a bandwidth issue from the host, but the driver should declare that error.

    Regards,

    JMMN