USB 3.2 Gen 2x2 and USB4 Designs: Type-A vs Type-C, MUX Requirement - Page 1
Forum section: electronics / projects

author: electronx
author_rank: Regular Contributor
timestamp: June 26, 2025, 08:48:01 am
content: Hi everyone,I’m currently learning about the USB protocol and designing a project, but I’ve encountered a few questions that I couldn’t find clear answers to. I’d really appreciate your input!1. USB 3.2 Gen 2×2 with SuperSpeed Type-A ConnectorAccording to the USB 3.2 specification, it states that USB 3.2 Gen 2×2 can support a SuperSpeed Type-A connector. This raises a question:If we use a SuperSpeed Type-A connector, the system would only utilize 1 lane for data transfer, leaving 1 lane from the host unused. Is this configuration valid, or is it against the USB specification to use SuperSpeed Type-A for USB 3.2 Gen 2×2? (The specification table seems to suggest it’s possible, but I’m unsure.)--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------USB 3.2 Gen 1×1 and Gen 2×1 DesignsWhen reviewing designs for USB 3.2 Gen 1×1 and USB 3.2 Gen 2×1, I noticed the following:If the host is in DFP mode, a single-lane connection can directly be made using SuperSpeed+ (SS+) Type-A connectors. This setup is straightforward and doesn’t seem to require anything additional.However, if we want to use USB Type-C with these standards:A MUX is typically required for orientation switching.Additionally, a USB Power Delivery (USB PD) controller is often needed to handle the orientation, as well as the role selection (DFP, UFP, or DRD).------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------USB 3.2 Gen 2×2 and USB4 Gen 3×2 DesignsI couldn’t find clear reference designs for USB 3.2 Gen 2×2, USB4 Gen 3×2, or USB4 Gen 4×2.When using USB Type-C with these standards, is a MUX still required for orientation switching?These standards use 2 lanes, and USB Type-C connectors have pins for RX1, TX1, RX2, and TX2. If all these pins are fully connected via hardwiring, is orientation switching still necessary? Or can the connection work without a MUX?I’m particularly curious about how the orientation affects the use of RX1/TX1 and RX2/TX2 pins.

author: physx
author_rank: Newbie
timestamp: June 26, 2025, 04:06:27 pm
content: Gen2x2 over a Type-A connector is not possible.It is x2, exactly because it uses two lanes. The Type-A connector does not have enough pins for two lanes, so you can only do Gen2x2 over a Type-C connector, which has four high speed differential pairs, instead of the two of the Type-A/B connectors and their variants.Yes, this does mean that the table is wrong.Technically, you can use a Type-A connector, wired to a Gen2x2 controller, but you can only connect one of the lanes, so there is no point. It would operate as a Gen2x1 connection, at 10Gbps.

author: electronx
author_rank: Regular Contributor
timestamp: June 26, 2025, 04:11:39 pm
content: Thanks for your answer, this is the same answer as I thought, but is there still a need for a mux when I use a usb type c port that uses 4 differential signals? In this case, can you provide an example of a pd ic that handles usb cc signals?

author: thm_w
author_rank: Super Contributor
timestamp: June 26, 2025, 11:50:27 pm
content: Quote from: physx on June 26, 2025, 04:06:27 pmIt literally says that limitation right on the table.3.2 is the spec, which it does fall under:https://www.kingston.com/en/usb-flash-drives/usb-30

author: ejeffrey
author_rank: Super Contributor
timestamp: June 27, 2025, 01:35:52 am
content: Quote from: electronx on June 26, 2025, 04:11:39 pmI don't believe you need a mux if you have an x2 controller. You just wire both lanes up to the port and whichever is available will be used.