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TUSB2046I: Can I connect one labtop to twenty USB devices with six TUSB2046Is?

Part Number: TUSB2046I
Other Parts Discussed in Thread: TUSB2077A

Dear TI guys,

On the environment of Windows or MAC, I would like to connect one labtop to twenty USB devices with six TUSB2046Is.

For your information, I attached my schematic in here. Please, refer to it.

In here,

==> Four downstreams of one TUSB2046I are used as the upstreams of four TUSB2046Is. So five TUSB2046Is are used for connecting 16 USB devices to labtop. Is it possible?

==> One TUSB2046I is seperately used for connecting four USB devices to labtop.

I will soon start the layout of my schematic. 

Please, give me any comments regarding the schematic and layout. Your any comment will be highly welcomed. If my schematic does not have any special defect, please tell me that.

Additionally, each USB device will be FTDI FT232H(single channel Hi-speed USB to UART IC). And the UART baud rate of FT232H is 115200. The operation of each USB device has been clearly verified. Namely, I would like to replace several commercial USB hubs with my own board. 

In your opinion, if there is any expected problem in my thought, please feel free to tell me that.

Best Regards,

Zunbae

TUSB2046I.pdf

 

  • Hello Zunbae,

    I have reviewed your schematics and these are my comments:

    • You must connect a pull resistor of 1.5kOhms on DP0 of each TUSB2046.
    • For the passive circuit of the reset signal, use a 15kOhm resistor instead of 22Ohm resistor. This applies for the hubs connected directly to the USB host. For the other hubs you will need to adjust the reset delay, since these hubs should wait until the first level hub is enumerated by the system.

    BTW, You can also use three TUSB2077A  to have 20 USB ports. 

    Regards,

    Joel

  • Dear Joel,

    Thanks much for your kind answers. I got it.
    But there is one uncertainty regarding the value of pull-up resistor attached to DP0 of four cascaded TUSB2046Is.
    What is your recommended value as the starting value?

    And for your information, I need USB hub which can endure 85 degrees.

    Best Regards,
    Zunbae
  • Dear Joel,

    There is a typo in my previous question.
    My intention is to ask you what is your recommended value for the resistor giving some delay to the reset signal of four cascaded TUSB2046Is.

    Best Regards,
    Zunbae
  • Dear Joel,

    In your opinion, it is good as the starting value to use 100KOhm and 2.2uF for the delay of reset signal at four cascaded TUSB2046Is?

    Best Regards,
    Zunbae
  • Hello Zunbae,

    You can use a 1.5kOhms resistor for all the hubs in DP0. It is per the USB specification for a full-speed device.

    For the reset signal, you can start with those values you mentioned and adjust them in case of enumeration issues. 

    Regards

  • Hello Zunbae,

    Please be aware that the TUSB2046 is a USB full speed hub.  If you connect USB high speed devices behind a full speed hub, they will drop to full speed operation.  An application connecting 20 devices at full speed would have low bandwidth.

    Regards,

    JMMN

  • Dear Joel and JMMN,

    Thanks much for your kind answers. I got it.

    Additionally about JMMN's concern of low bandwidth due to the cascaded connection,

    ==> I am also worried about that even though my application is fixed and limited. The used USB devices are FTDI FT232HLs which translate USB to UART 115200 baud rate.

    ==> In my guess, for handling the UART 115200 baud rate without any problem, the required bandwidth from USB side will be maybe 3Mbps.

    ==> The TUSB2046Is of the first tier will well do it. But about the TUSB2046Is of the second tier, I am not sure about good operation on the base of JMMN's advices.

    ==> In your opinion, is there no way except using high speed USB hub solution? 

    Best Regards,

    Zunbae

  • Hi Zunbae,

    There will be little impact from using tiers of EVMs, but 20 devices trying to share 12 Mbps of bandwidth may not be a good user experience. If only a few devices are active at a time, a full speed hub would be acceptable but if all the devices are running at once I would recommend switching to a USB 2.0 hub like the TUSB4041.

    Regards,
    JMMN
  • Dear JMMN,

    Thanks much for your advices. Got it.

    Best Regards,

    Zunbae