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tusb2046b usb 2.0 and power issues

stephen vincent
Prodigy 110 points
Other Parts Discussed in Thread: TUSB2046B

I have laid out a usb hub for a project using the tusb2046b.  I mainly based my design off of the reference design labeled figure 11 in the data sheet.  When I plug in mass storage devices it says that the max power is exceeded and I would assume thats because of hte current limit of only 100ma per port.  It looks like I need to move to a self powered version rather than a bus powered one.  Also When I plug in the device (which i'm using now for this keyboard and my mouse) it says that I am limited to usb 1.1 speed.  I was under the impression that this usb controller chip was capable of usb 2.0 operation.  Is there steps I need to take in order to make it run at usb 2.0 speed or did I choose the wrong IC altogether?

  • 0
    TI__Mastermind 18655 points

    Hello Stephen,

    USB 2.0 is a specification that defines three different speeds of operation - USB low-speed (1.5 Mbps), USB full-speed (12 Mbps), and USB high-speed (480 Mbps).  The USB 2.0 specification replaced the USB 1.1 specification and that is no longer a technically accurate description of a device. 

    To be complaint a peripheral device must support at least one speed.  A hub can be compliant if it only supports LS & FS and is intended for "embedded" applications.  Therefore the TUSB2046B (also the TUSB2036 and TUSB2077A, ) are all USB 2.0 compliant as full-speed capable embedded hubs.
     
    Regards,

    Joel 

  • 0
    TI__Mastermind 18655 points

    Stephen,

    If the downstream devices are never going to draw more than 100mA, the reference design (Figure 11) will work, but take in mind that if this limit is not controlled you are going to have many over-current events.

    The mode of operation on the TUSB2046B is controlled with the BUSPWR terminal, but it cannot change dinamically during operation.

    Regards,

    Joel