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I'm trying to design my USB-HUB, because not so many commercial ones offer the solutions I need; My intentions would be to have a per-port power control, so I can switch on/off devices as I please (The idea is so that I can leave many devices plugged in, while only powering the one I need; for example a printed, logic analyser, etc.)

This turned out to be rather difficult task, because many USB HUBs offer a disable port feature, but they are not really descriptive of how it works. For example a USB HUB IC USB2514B can have ports disabled, but can it be done on the fly? This IC would of course be pair with a power-controller IC such as TPS25820/1, but I worry if I only turn off the power lines, the downstream device still may be powered or partially powered via the D+ and D- lines and I would rather have them completely shut down. (The HUB can be 2.0)

How is this done? Or how should it be done? Thanks :)

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    \$\begingroup\$ You can buy USB hubs which do completely turn individual ports on & off. In my company, the QA team I work with uses them for some of their automated testing of our devices. I don't know the specific device models or chipsets though. \$\endgroup\$
    – brhans
    Commented Jul 24, 2023 at 17:27

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If power is off the downstream devices cannot get powered via data wires. You really don't need to think about it.

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  • \$\begingroup\$ Well you can power a CMOS chip only via a reset pin and ground, sooo \$\endgroup\$
    – Kralik
    Commented Jul 24, 2023 at 17:17
  • \$\begingroup\$ @Kralik Yes but USB does not work like that. USB data pins idle at 0V by the host side until the device side pulls data line up and it can't do that if it has no power. \$\endgroup\$
    – Justme
    Commented Jul 24, 2023 at 17:22
  • \$\begingroup\$ Oh, that would change a lot, thanks! I lacked this knowledge! \$\endgroup\$
    – Kralik
    Commented Jul 24, 2023 at 20:42
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Is that what you are looking for? enter image description here

Designing a USB hub to only add switches on the power seems to me like a lot of work. Even more when there are commercial solution widely available. But for the sake of it, if you are using USB2, it's as simple as placing a switch on the power line. The only caveats to that is some device can be self powered, so they will communicate even when turned off (had this issue with commercial switches). If you want to also break the data lines, you can, but, it is trickier since they are somewhat high frequencies.

If you want to do USB3, it is way more complex.

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  • \$\begingroup\$ Well that advertisement clearly is incorrect on the technical details (5 Gbps on USB 2.0?) so I wouldn't trust the switches to be correctly designed either. \$\endgroup\$
    – Ben Voigt
    Commented Jul 24, 2023 at 15:09
  • \$\begingroup\$ Thanks for that comment. I am aware of those HUBs, but indeed, they have the switch directly connected to the power input, which I thought is not a really a great idea desgin wise. Also, self powering devices are not my concern, I don't like more the fact that it can be powered through the D+ and D- lines. \$\endgroup\$
    – Kralik
    Commented Jul 24, 2023 at 15:44
  • \$\begingroup\$ Power don't really go trough data lines, I wouldn't worry about that. Switching data line is a lot trickier then it might look. \$\endgroup\$
    – Julien
    Commented Jul 24, 2023 at 16:15

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