Isolating USB 3 - Page 1
Forum section: electronics / projects

author: fluxgate
author_rank: Contributor
timestamp: February 19, 2022, 11:19:35 am
content: Hey,I'm just curious if it's easily possible to isolate USB 3.0 just using inductive transformers.USB 2.0 is really a pain in the ass in terms of isolating, because it needs to be DC correct and birectional (?!).However, if you only use USB 3.0 Host and Slave, shouldn't it be as cheap as isolating Ethernet/LAN?!

author: wraper
author_rank: Unknown
timestamp: February 19, 2022, 11:54:27 am
content: The cheapest option IMHO would be buying a fiber optic USB 3.X cable and adding an isolated DC/DC converter to it for VBUS.

author: jpb
author_rank: Super Contributor
timestamp: February 19, 2022, 12:06:42 pm
content: Commercial USB3 isolators are quite expensive but might give you some ideas, e.g. the Intonahttps://intona.eu/en/products/7055-d

author: Renate
author_rank: Super Contributor
timestamp: February 19, 2022, 02:40:42 pm
content: Are you sure you're talking about/needing USB 3.0?I mean, you might just be talking about Type C connectors carrying USB 2.0

author: SiliconWizard
author_rank: Super Contributor
timestamp: February 19, 2022, 07:20:14 pm
content: The most reasonable approach is often to isolate *after* the USB link - that's true also for USB 2.So basically you have some USB interface without isolation, and isolate data after that (and power if you also need power from USB, which is not always the case). It especially makes sense if your required data throughput is significantly lower than the max throughput of USB - it'll be much simpler and cost a lot less to isolate than doing that upfront, that is directly on the USB bus.Of course what I said applies if you're designing your own USB device. If you need to isolate existing devices, that's another matter.

author: NiHaoMike
author_rank: Super Contributor
timestamp: February 19, 2022, 09:54:19 pm
content: USB 2.0 can be isolated for relatively cheap using USB/IP over Ethernet or Wifi.USB 3.0 could possibly be isolated using SFP modules.

author: nctnico
author_rank: Super Contributor
timestamp: February 19, 2022, 10:20:15 pm
content: Quote from: NiHaoMike on February 19, 2022, 09:54:19 pm10Gbit SFP modules would work I think... Maybe also for PCIexpress. Unless latency is a problem. Sounds like an interesting experiment! The question is whether a USB3.0 device works without the USB2.0 lines.

author: NiHaoMike
author_rank: Super Contributor
timestamp: February 19, 2022, 10:55:14 pm
content: Quote from: nctnico on February 19, 2022, 10:20:15 pmI have tried that before, it does. Not sure if it holds true for USB 3.1 or newer.

author: TiN
author_rank: Super Contributor
timestamp: February 20, 2022, 04:00:35 am
content: I have a USB3 fiber isolator from Icron :https://www.icron.com/products/icron-brand/usb-extenders/fiber/usb-3-0-spectra-3022/It used SFP fiber and two boxes. There is NO USB2.0/1.1 link between boxes, so only USB3 devices work. Bought it before knowing that.Inside just a single PCB with USB3 chip and interface to fiber port.

author: Renate
author_rank: Super Contributor
timestamp: February 20, 2022, 10:57:40 am
content: The USB spec requires USB 3 to have USB 2.Like NiHaoMike I've taken a USB 3 device and cut the USB 2 traces and it still worked.YMMV.If you had a problem with a link (or host) that refused to work without a USB 2 for the USB 3 it should be possible to program a USB 2 µC with the right descriptors for USB 3 so that the host would switch to USB 3. Of course the µC wouldn't have to do any real function.