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TUSB8041: USB 3.0 12 port HUB daisy chain vs cascade confuguration

Jeremy Novoa
Prodigy 130 points
Part Number: TUSB8041

Hello,

I am looking into using the TUSB8041 to design a 12 port USB 3.0 HUB. I know that the there are some propagation delay considerations when designing a multiple port HUB, but i am looking for a recommendation on what configuration works best. Attached are my two approaches (PDF files OK?). Please feel free to add any recommendations when working with ganged  TUSB8041. 

Additional, is there any application note that you can point me out on this subject?

Thank you,

-JUSB_HUB_TIER_4.pdfUSB_HUB_TIER_6.pdf

  • 0
    TI__Expert 7395 points
    Hello Jeremy,

    According to the USB 2.0 specification, the maximum number of tiers allowed (including the root hub on the USB Host) is seven. So that is a maximum of 5 daisy chained hubs.
    Both configurations shown on the PDF files you attached would meet this requirement, although it is preferable to use the configuration with the fewest number of tiers (USB_HUB_TIER_4.pdf); not only because of the propagation delay, but also because it would allow users to further expand their topology with additional USB Hubs regardless of the port they are connected to.

    We have no application note detailing ganged operation, but I think the TUSB8041 datasheet is clear enough mentioning all that needs to be known on the subject.

    To configure the TUSB8041 for ganged operation, you can either have a PU resistor on the "GANGED/SMBA2/HS_UP" terminal, or by writing a 1 to bit 3 on the "Device Configuration Register" (offset 0x05) either through an external EEPROM or SMBus Master.

    A ganged hub switches on power to all its downstream ports when power is required to be on for any port. The power to the downstream ports is not switched off unless all ports are in a state that allows power to be removed.
    Also when a ganged hub senses an over-current event, power to all downstream ports will be switched off.

    Please let me know if you have any specific questions on this matter.

    P.S. TUSB8041A is recommended for all new designs over TUSB8041. Both devices are pin to pin compatible. Please consider using TUSB8041A instead.

    Regards,
    Jorge
  • 0
    Prodigy 130 points
    Hi Jorge,

    Thank you for your answers. I miss spoke when I said "ganged TUSB8041" I meant application note on multiple TUSB8041 connected together to create 4+ port HUB.

    One more thing, one of my requirements is to be able to physically identified all 12 ports. I know that typically the host assigns the port# and this may be random. Is there a way to uniquely ID each port, so no matter what the host assigns I still know which port is which?

    Last, do you know if daisy chain vs cascade has any effect in the order of port enumeration?

    Thank you,
    Jeremy
  • 0 in reply to Jeremy Novoa
    TI__Expert 7395 points
    Jeremy,

    There is no unique identifier for each downstream port.
    Your software would need to scan the entire USB bus to determine the location of each device.

    You may want to check USBView's source code : github.com/.../usbview

    Regards,
    Jorge
  • 0 in reply to Jorge Llamas (SWAT)
    Prodigy 130 points

    Thanks for your help!

  • 0 in reply to Jorge Llamas (SWAT)
    Prodigy 130 points

    Hi Jorge,

    I am trying to calculate the require power for this 12 port hub. In the TUSB8041 data sheet section 7.7 there is some parameter so with that information I am trying to estimate base on my configuration and connected devices.

    All my connected devices will be USB2.0 and according to the datasheet if my host is USB2.0 and my connected devices are USB2.0 the current drawn from the TUSB8041 is 3.3V @ 76mA and 1.1V @ 86mA. What I don't know (not on the data sheet) is what happens when you cascade the TUSB8041.

    For example, if my host supports USB3.0 and USB2.0 and I have two TUSB8041 cascaded and all my connected devices are USB2.0, is it true that the two TUSB8041 will be working in "USB2.0 mode"? If true, is the current drawn for each TUSB8041 will be 3.3V @ 76mA and 1.1V @ 86mA plus the current drawn by the connected devices?

    Thank you,

    Jeremy