+ Post New Thread
Results 1 to 4 of 4
  1. #1
    Newbie level 4
    Points: 61, Level: 1

    Join Date
    Oct 2018
    Posts
    5
    Helped
    0 / 0
    Points
    61
    Level
    1

    USB2 hub before USB3 port

    I'm designing a board which has a single USB 2.0 PHY, currently connected with the high speed pairs to a USB 3.0 port. I have another part on the board that needs a USB 2.0 connection. Can I just use a 2-port USB2.0 hub IC to split the USB2 interface to the device and the USB3 socket? Will it cause issues for the USB3 port if the USB2 part of it is going through a hub? Or do I need to use a USB3.0 hub and only use the USB2 part of it for the second device? Footprint is an issue and I'd rather use the smaller parts if I can do it.

    •   AltAdvertisement

        
       

  2. #2
    Super Moderator
    Points: 258,502, Level: 100
    Awards:
    1st Helpful Member

    Join Date
    Jan 2008
    Location
    Bochum, Germany
    Posts
    45,134
    Helped
    13721 / 13721
    Points
    258,502
    Level
    100

    Re: USB2 hub before USB3 port

    a single USB 2.0 PHY, currently connected with the high speed pairs to a USB 3.0 port
    What do you mean? USB2.0 (1.5/12/480 MBPS) uses only a single D+/D- pair. USB 3.0 "Superspeed" interface uses two additional differential pairs. An USB 3.0 port is always downwards compatible to connect USB 2.0 devices or hubs by simply leaving the SS pairs unconnected. Similarly an USB 3.0 enabled device or hub can always connect to an USB 2.0 downstream port.



    •   AltAdvertisement

        
       

  3. #3
    Newbie level 4
    Points: 61, Level: 1

    Join Date
    Oct 2018
    Posts
    5
    Helped
    0 / 0
    Points
    61
    Level
    1

    Re: USB2 hub before USB3 port

    here's a rough illustration of what I mean:
    Click image for larger version. 

Name:	usb2hub.jpg 
Views:	8 
Size:	119.0 KB 
ID:	150445
    I'm talking about on the host board, between the PHY and the ports. Basically, are the USB2 and superspeed interfaces in the USB3 port totally independent, or are they more tightly linked? Is it going to cause a problem for the USB3 port if the USB2 portion of it goes through a hub IC before it hits the PHY?



    •   AltAdvertisement

        
       

  4. #4
    Super Moderator
    Points: 258,502, Level: 100
    Awards:
    1st Helpful Member

    Join Date
    Jan 2008
    Location
    Bochum, Germany
    Posts
    45,134
    Helped
    13721 / 13721
    Points
    258,502
    Level
    100

    Re: USB2 hub before USB3 port

    Guess it doesn't work. But you can check the spec or simply try.



--[[ ]]--