I have to design a big USB-hub that only full- or low-speed USBs will be connected to the downstream ports.

I've already made it with FE1.1 and four FE2.1. The first one converts 1 USB to 4 USBs, and each output will feed four FE2.1 converters, making 4*7 = 28 ports.

I did not use all the ports but it looks fine for the 8 ports I tested.

My questions are:

  1. Has anyone ever designed such a big USB hub? What kind of ICs did you use?

  2. I used these two cheap ICs. Does anyone here havr experience with a better IC?

  3. How important is MTT selection versus STT? I feel the 1 to 4 converter which will feed the other 4 converters plays the key-roll.

  • \$\begingroup\$ I think it depends on compromise for low latency and high thruput with mixed devices on same bus. STT seems to be better + cheaper when all the same type. MTT is better for mixed devices. cypress.com/documentation/application-notes-obsolete/… \$\endgroup\$ – Tony Stewart Sunnyskyguy EE75 Apr 30 '19 at 20:11
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    \$\begingroup\$ What in the world is the purpose of this? You'd have to be making a lot of these for doing a custom one to make more sense than plugging together off the shelf hubs, and if you are going to that trouble you should probably try to optimize what is accomplished by each USB port first. What are you going to be connecting 28 of? \$\endgroup\$ – Chris Stratton Apr 30 '19 at 20:25
  • \$\begingroup\$ If you are designing this on spec, I'm curious about your 14 Amp, 5V supply. Are these USB 2 or USB 3? If you wanted USB 3, you would need to supply up to 25.2 Amps. \$\endgroup\$ – Ron Beyer Apr 30 '19 at 20:56
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    \$\begingroup\$ @SunnyskyguyEE75 "STT seems to be better" - no, STT is never better. If you have 7 full-speed devices, a hub with STT will have to share the FS bandwidth between all 7 devices, so you will have only 1700 kbits/s per device. A MTT hub will give you full 12,000 mbps FS bandwidth for each of 7 devices. \$\endgroup\$ – Ale..chenski May 3 '19 at 1:28
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    \$\begingroup\$ @SunnyskyguyEE75, both STT and MTT work on split transactions. Only the STT has one TT for all ports (and thus must MUX the output and share its buffer), while MTT has TT and corresponding buffer per each DFP. \$\endgroup\$ – Ale..chenski May 3 '19 at 2:48

There are plenty of 28+ port hubs on the market, "Manhattan", ORICO industrial grade, and even 97-port hub with 400W power supply. All multi-port hubs are built hierarchically out of 7-port hubs and combinations, so they encroach into 5-hub-chain rule, and need to be better connected to root ports to avoid refusals to connect.

The MTT function is critically important for performance reasons, especially if you need all devices to be LS and/or FS and have a lot of them.

  • \$\begingroup\$ Thanks every one for sharing your comments. I made the design, using a 7-port FE2.1 which feeds 7 other downstreams. Three downstreams are used for regular usage and the other 4 of them are inputs to the upstream of four FE2.1, making 4*7 = 28 ports. The design works but there are bugs. When I use most of ports, the windonws 7 or 10 pop-up a msg showing a device is plugged-unlpugged. While there is no device unlpugged!! I am wondering if anyone has designed a similar thing. My design is really similar to the Manhattah USB-HUB. They are using the FE2.1 mux. \$\endgroup\$ – amir_sh Aug 11 '19 at 20:42

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