I've been working on this design for a client for a little while now. I can't go into full specifics on it but the basic design is a USB hub. The IC I picked at the time met the design requirements that were established (USB5807C). The hub allows for 1 host and 7 downstream devices to be connected. From what I can see, the chip does support a USB Type-C connection. My client's design changes are a switch to Type-C for the host connection and HDMI output to make use of Type-C's Alt Mode for HDMI. I have some experience working with USB 2.0 and 3.0, but I'm new to Type-C in general and especially the HDMI mode. My question has two parts:

  1. Is it possible to work in the HDMI port into the current hub design using the USB5807C or would I need to use a different IC?
  2. How do you go about working in the HDMI support while also having the same pins also acting as a hub?

I know that it's possible to set up because there are a bunch of similar type-c hubs that also offer HDMI. I would really appreciate any help on this a great deal, thanks! :D

  • \$\begingroup\$ Afaik you can't simultaneously run SuperSpeed USB and Alt-mode HDMI over the cable at the same time. Is this what your client is expecting? The pin mapping here shows how the USB-3 TX/RX pairs are repurposed as HDMI signals, and only leave the USB-2 D-/D+ and Vbus alone. You'll also only get HDMI out from a USB-C to HDMI cable if the USB host you're plugged into is capable of putting the HDMI signals out onto its USB-C port. \$\endgroup\$ – brhans Dec 9 '20 at 1:40
  • \$\begingroup\$ A few month back, I've disassembled a broken USB-C hub/docking station. It contained four main chip: (1) A USB multiplexer that can split (and join?) USB data lanes. (2) One or two of the lanes go to a HDMI chip, which converts the DisplayPort data stream to HDMI. (3) Other lanes go to a USB hub chip. (4) A USB power management chip is responsible for power delivery (from an external power supply via the docking station to the host). Maybe this information is helpful. I didn't record the specific chips unfortunately. \$\endgroup\$ – Codo Dec 9 '20 at 8:47
  • \$\begingroup\$ Regarding HDMI: If I'm not mistaken, there are two options: sending HDMI or DisplayPort data over the USB-C cable. Sending HDMI is very rare and rarely supported. Most adapters (including cables with USB-C on one and HDMI on the other side) are based on DisplayPort and convert it on the side where the HDMI connector is. \$\endgroup\$ – Codo Dec 9 '20 at 8:49

Not sure if HDMI over Type-C exists, but the DisplayPort over Type-C can coexist with USB 3.1 functionality. And DP can be converted into HDMI if needed.

Type-C cables have four high-speed twisted-pair transmission channels. As a plain DP port over Type-C, all four lanes are used for full-scaled DP. In so-called "Alt-DP mode" two lanes are used as Rx and Tx for USB 3.x connection, and other two lanes are used for DP:

enter image description here

This Texas Instrument article provides more details on the variants of connectivity, and offers high-speed multiplexors to implement this.

I am not sure if there are USB3 hub controller ICs that support DP pass-through, but you certainly can use stand-alone demux-mux to make your own bypass for DP lines, provided that you re-create all necessary CC and PD control on both sides of the hub.

  • \$\begingroup\$ I was looking around and found this IC (TUSB1064) that I believe is exactly what I would want to use for this type of application, right? So if I'm right, the order would go like this: You have the male connector for the hub, then that goes into both the TUSB1064 and the USB5807C. Then the DisplayPort outputs on the TUSB1064 I would have feed into another IC that would convert the DP signal to HDMI? Is that right? \$\endgroup\$ – TokyoScarab Dec 11 '20 at 0:08

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