I have a StartTech.com 7-port USB 3.0 HUB plugged into a PC. There are seven devices plugged into the hub, and I'm running the 12VDC external power to the HUB as well. The HUB is plugged into a USB 3.0 port on the PC.

Scenario 1:

If I UNPLUG the power, all devices continue to operate normally. Combined, in full operation, they collectively pull just under 400ma at 4.93VDC. When idle, they draw just under 100ma. Everything is good.

Scenario 2:

If I return power, that is, I plug-in the 12VDC external power source into the HUB while everything is running, the HUB performs what appears to be a power-on-reset. All devices drop, the current goes to 0.00ma and then the devices come back (via plug-n-play). However comma, SOME devices do not. They don't recover. Windows reports that the hub didn't reset properly.

My question is - is this a normal thing for USB HUBS to do? I've got a number of others and none of them perform a PoR.

I called StarTech.com and got a rather vascillatory response - they aren't sure either.

I'm essentially simulating a power loss scenario. I can't have random pieces of kit not returning to functionality after a PoR from the HUB. The problem really is academic at this point - yes, replace the HUB; simple. However, I'm concerned that we've invested in a number of these if this is normal / to USB-IF spec or flies in the face of convention?

  • I've had similar issues with applying power to USB power banks. Some switch the USB power off permanently, some dont. Some even switch the USB power off momentarily, and then turn power back on. We tried tens of power banks and there was obviously no standard behavior (not even amongst the same brand). My point is, there may be no answer to a "standard" about this. – Wesley Lee Apr 7 '16 at 18:46
  • This question is a better fit on SuperUser I think, as it's a PC hardware question more so than an electrical engineering question. – Adam Lawrence Apr 7 '16 at 20:18
  • @Adam - probably true, however, as I have experienced so many times, there's always room for questions like this to go either way. A PoR function is a chip-level design feature and something that can be handled in firmware. The question is directed to see if this is an industry standard convention for these devices (PoR on external power application for HUBs already operating plugged into host ports) or if this appears to be flying in the face of convention. – Redgum Apr 7 '16 at 20:54
  • @Redgum - Unless you crack open the hub and/or power supply and provide waveforms or measurement, you're essentially asking about "consumer electronics" and not electrical design. Also, when it comes to what constitutes industry standard for USB hub behaviour, I really think that this isn't the correct SE site. – Adam Lawrence Apr 7 '16 at 20:58

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