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TUSB2077A Multiple Tier Configuration

Nathaniel Wilson
Intellectual 1990 points
Other Parts Discussed in Thread: TUSB2077A

Hi team,

I am trying to gather some information on a 3-tier hub network that has 36 devices on it using the TUSB2077A. I read in elsewhere in the forum (http://e2e.ti.com/support/interface/digital_interface/f/130/p/157867/573707.aspx#573707) that the first tier will be enumerated after 300ms. Is this a good rule of thumb? Also, what is the reasoning behind 300ms?

Finally, is there any collateral (reference designs, timing for enumeration, etc) for setting up a tiered network with the TUSB2077A?

 

Thanks!

  • 0
    TI__Guru* 76130 points

    Hello,

    That is not a rule of thumb, the enumeration process highly depends on the downstream devices connected and the USB host. 

    The only specification is that a downstream device should be able to respond to the host within 100ms after power is applied.

    Having several tiers do requires certain reset power-up constraints. the recommendation is to release the reset of the first tier and so on.

    You can accomplish this by using a passive power-up reset with a RC circuit and setting the time constant longer for the downstream tiers.

    Regards.

  • 0 in reply to Elias Villegas M.
    TI__Intellectual 1990 points

    Thanks for the help Elias. I see now where you got the 300ms from.

    I have also noticed that the PON line will briefly return back high after a suspend. Is this supposed to happen? That doesn't seem like that should be the case.

    Finally, is there anything about the HUBCFG pin that would prevent it from being used to enable another onboard I/O chip instead of using it as an LED indicator?

    Thanks again!

  • 0 in reply to Nathaniel Wilson
    TI__Guru* 76130 points

    Hello,

    The PWRON# signals will be de-asserted when the hub is in suspend state.

    The HUBCFG signal is not the bets choice for a chip-select, every time the Hub is reset or goes into suspend or the USB host send a software reset, this pin (HUBCFG) will toggle.

    Regards.