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TUSB2077 HUB not working as 2.0 USB HUB

Joaquim Barrera
Prodigy 20 points
Other Parts Discussed in Thread: TUSB8040A

Hello,

I've designed a USB HUB using TUSB2077. It works fine, but just at USB 1.1. When I plug it into the PC, the typical message pops-up "This device can perfom faster".

We are using a 6 MHz XTAL with MODE pin tied low.

Here is the sch, with no pull-ups on OC# pins, but they actually are in the PCB (that's why it works, at least at 1.1)

http://db.tt/KYsD5Szp

I followed all the specifications... Low ESR 100uF caps. XTAL circuit cap.s ans res. I don't know, I guess it's just a matter of a little detail, but I can't see it.

Thank you.

  • 0
    TI__Guru* 76130 points

    Hello Joaquin,

    The TUSB2077 will not transfer data at 48Mbps, it only transmit at 12Mbps rates.

    The USB Org allow a hub to be specified as USB 2.0if the following:

    A hub is compliant:
    • if it only supports LS & FS and is intended for "embedded" applications (think keyboards, test equipment, consoles, etc. where one or more of the ports is permanently attached to a device in the box.
    • "stand-alone" hub is required to support high-speed data transfer rates to be compliant.

    So that is why the TUSB2077 is USB 2.0 compliant but it will not transmit at 48Mbps data rates.

    Regards.

  • 0 in reply to Elias Villegas M.
    Prodigy 20 points

    Hello and thank you for the quick answer. I still have a couple of questions.

    So if the TUSB2077 only accepts 12 Mbps transfer rates, what exactly means that is USB 2.0 compliant? What is the meaning of:

    "The downstream ports support both full-speed and low-speed devices by automatically setting the slew rate according to the speed of the device attached to the ports"


    And the last question. What exactly should I do to build a USB HUB that could reach more than USB 1.1 transfer rates? Should I use another USB HUB or it's a matter of some electronic components?

    Thank you again.

  • 0 in reply to Joaquim Barrera
    TI__Guru* 76130 points

    Joaquim,

    What transfer rate do you need?

    USB 1.1 specifies two transfer rates:

    1.5 Mbps --> low-speed

    12Mbps --> full-speed

    USB 2.0 specifies three transfer rates, the two above and 48Mbps which is high-speed.

    Saying that a device is USB 2.0 compliant implies a lot of characteristics, but talking only about transfer rates it mean that supports 48Mbps.

    The TUSB2077 only supports 12Mbps and 1.5Mbps, you can not make it support 48Mbps.

    If you need the 48Mbps you will need another hub, we have a USB 3.0 hub which also supports high-speed (TUSB8040A)

    Regards.