I am attempting to design a basic 7 port USB hub that will be used in a custom 3D printed case. It will connect to a FPGA device and be powered by a 5V adapter through a barrel plug. I'm stuck on a few things though.

  1. The data sheet puts 100uF caps on each USB port. Other people's designs I found didn't include those. I read somewhere that having caps on the ports could cause problems with "hot swapping". Does anyone have experience with that?

  2. Can I connect the 5V from the barrel jack directly to all the VBUS connections without adding any additional circuitry? I saw examples online where they tied it directly to the input from the micro USB. However, I also found someone who mentioned that this might cause a backfeed of power to the computer (or in this case, the FPGA). Could I just leave the power pin from the micro USB unconnected and rely on power from the barrel jack?

  3. Since this isn't going to be an OTG device, can I leave the "ID" pin from the micro USB jack unconnected or does something need to be done with that?

Thanks in advance for any feedback!


Data Sheet

  • 1
    \$\begingroup\$ Please edit the question to limit it to a specific problem with enough detail to identify an adequate answer. \$\endgroup\$
    – Community Bot
    Commented Sep 30, 2021 at 18:02
  • 1
    \$\begingroup\$ Do you understand the basics of how power and data flow in a USB tree? Do you know the difference between a hub's upstream port and downstream ports? You say the hub will be connected to an FPGA, but is the FPGA serving as host, one of 7 downstream devices (others of which may be connectorized ports), or performing monitoring and control (e.g. switching ports on and off) only? \$\endgroup\$
    – Ben Voigt
    Commented Sep 30, 2021 at 21:35
  • \$\begingroup\$ Or is the FPGA not part of your hub at all, and connected through a cable? \$\endgroup\$
    – Ben Voigt
    Commented Sep 30, 2021 at 21:36
  • \$\begingroup\$ The FPGA (DE-10 Nano specifically) runs on Linux and the hub will function the same as it does on a traditional PC. It will connect via a micro USB cable. Peripherals (keyboard, mouse, game controllers, etc.) will then connect to any of the 7 USB-A ports and be able to communicate that way. Off the shelf hubs can be used, but I needed a specific configuration for the enclosure I've designed for the FPGA. That's why I'm attempting to design this custom hub to suit my needs. FWIW it should be capable of being used on a standard PC as well if desired. Sorry for any confusion! \$\endgroup\$
    – OnCor
    Commented Oct 1, 2021 at 12:40
  • \$\begingroup\$ From what I can see (and remember since you haven't provided a part number, none of us can see any documentation except the schematic you pasted in the question), that USB hub chip is not suitable for a self-powered device, only for bus-powered. A self-powered capable USB chip needs, in addition to the ability to sense upstream power even when local power is present, to send different values in the USB descriptor. I don't see any way to do either of those with this chip. \$\endgroup\$
    – Ben Voigt
    Commented Oct 1, 2021 at 17:10


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