High-speed USB isolator

[free_electron]

The problem with isolators is that they inject roundtrip delay because they need buffering. for 480mb/s the delay is just too long.

the solution is to use a simple cheap, self powered, hub inbetween. if you fry anything it'll be the hub.

[mikeselectricstuff]

The problem with isolators is that they inject roundtrip delay because they need buffering. for 480mb/s the delay is just too long.

the solution is to use a simple cheap, self powered, hub inbetween. if you fry anything it'll be the hub.

Unless you get a few tens of amps flowing through the ground return...
Or the "frying" event is sufficient to arc between sides inside the hub chip.


 

[nctnico]

I think the USB over ethernet is the simplest solution. Ethernet is isolated by default (around 1kV-ish) and if you need more isolation then you can switch to fibre.

[jcbottorff]

Just an update on available USB isolation products. This site http://hifimediy.com/Accessories/high-speed-usb-isolator-480Mbps says they have a high speed USB isolator (auto selects 1/12/480 mbps) for about $80. There is also a CoolGear high speed USB isolator for about $190 at https://www.amazon.com/dp/B01E68ME7S

There also are reports of a long Corning USB 3.0 5 Gbps optical cable for $100, https://www.amazon.com/dp/B00JOJRF6K  It doesn't transmit power, so you need an isolated powered hub.

I just bought, and am about to return, a $40 isolator which claimed low and full speed, but reality was it only supports full speed. It's the single port version of https://www.aliexpress.com/item/1-to-4-Usb-isolator-digital-isolation-usb-2-0-hub-for-audio-signal-power-supply/32325766995.html from an Amazon seller. The aliexpress website spells out full speed only, the Amazon vendor didn't. Adafruit has a bare isolator, with a low/full speed switch for $35 https://www.adafruit.com/product/2107

[David Hess]

If its a desktop PC:  What about using cheap PCI/PCIexpress USB adapters, if one blows you don't lose a motherboard.

Doing that is better than nothing but still requires luck to prevent system damage and does nothing to prevent a destructive ground loop.  USB was not designed to connect instrumentation or operate across AC power domains.

The big problem with USB isolation is that it is half duplex effectively requiring an isolation barrier to also operate as a hub to decode what is going on.  This makes even 12Mb/s Full Speed isolation difficult.  If you want 480Mb/s USB 2.0, then you will have to pay and other solutions become economical.  Use Ethernet if you can.

[nidlaX]

Just an update on available USB isolation products. This site http://hifimediy.com/Accessories/high-speed-usb-isolator-480Mbps says they have a high speed USB isolator (auto selects 1/12/480 mbps) for about $80.

I can vouch for hifimediy as a vendor (their USB DAC is quite good), but I have not used their isolator.

On another note, have you ever looked at the Corning USB 3.Optical cables? It looks like a very nice solution using optical transceivers / fiber as a bridge between USB A endpoints. These are good for up to 5 Gbps!

Product page: https://www.corning.com/optical-cables-by-corning/worldwide/en/products/usb-optical-cables.html
BH Photo for a 33' cable: https://www.bhphotovideo.com/c/product/1057862-REG/optical_cables_by_corning_aoc_acs2cva010m20_type_a_plug_to.html

Also, here's an HV isolated USB 3.0 hub for reference:
http://buy.advantech.com/USB-4630-AE-USB-4630-AE/USB-4630-AE/model-USB-4630-AE.htm

I must say, a lot of great USB isolation options have emerged in the last couple of years.

[Mark]

Just an update on available USB isolation products. This site http://hifimediy.com/Accessories/high-speed-usb-isolator-480Mbps says they have a high speed USB isolator (auto selects 1/12/480 mbps) for about $80.

I just ordered one, thanks!  These definitely come in handy when trying to probe isolated ADC channels using a USB 'scope like the Analog Discovery. 

[Lord of nothing]

http://www.delock.de/produkt/62588/pdf.html?sprache=en

[mikeselectricstuff]

http://www.delock.de/produkt/62588/pdf.html?sprache=en

That's full speed only, not high speed

[f5r5e5d]

https://www.amazon.com/dp/B00JOJRF6K sounds like it isn't isolated, runs copper the length of the cable to power the optos

[MrW0lf]

Due to request in other thread:

Olimex USB-ISO is 12Mbps indeed, if want go higher found some other options, but do not have them:
https://hifimediy.com/hifimediy/high-speed-usb-isolator-480Mbps
http://www.coolgear.com/product/usb-isolator-high-speed
Should anyone get/have these or similar please report back. I'm very interested in 480Mbps option.
But back to Olimex, ok, did cut my puppy open 





..and ADUM4160 it is!

[voltsandjolts]

Not cheap (GBP99) but this works for me:

https://www.lindy.co.uk/usb-firewire-c4/100m-cat-5-usb-2-0-extender-lite-p7368

[Lord of nothing]

is an extender not isolator?!

[voltsandjolts]

is an extender not isolator?!

It's both!
Uses ethernet isolation magnetics.

Edit:
Uses "Jiangsu Qinheng Co., Ltd"(!!!?) CH317
http://www.wch.cn/product/CH317.html
 + Realtek RTL8211E to drive the magjack

[LaurentR]

Just got my HifiMeDIY USB2 isolator.
https://hifimediy.com/high-speed-usb-isolator-480Mbps
$89, shipped from Vava'u, Tonga 

It is based on a Silanna ICE USBB chip for data lines and an isolated 5V-5V DC-DC converter for power.
Silanna press release: http://www.prweb.com/releases/2015/10/prweb12995871.htm
And yes, soldering quality is "moderate".

I have only tested it with my old Saleae Logic 16 and it does the job at full acquisition speed (which is what I bought it for).

[splin]

The ones I mentioned go all the way. They are sold as USB Extenders which use CAT5E cable as the transmission media, but they use ethernet Mag Jacks and are isolated.

http://www.trinetusa.com/images/spec_sheets/electronic/R042-EXT-C5E.pdf

404 Not Found? (Same goes for your previous link).

I guess you mean this: http://www.trinetusa.com/product_description.php?PNo=173 Seems it could be a good solution at $88 - in the US. Probably $888 in the UK with shipping, duty, highway robbery handling fees, VAT on all the above etc, etc.

What a horrible and uninformative website!

[nidlaX]

I'm surprised that no one has mentioned Corning's optical USB3.0 cable.

I did!

[nidlaX]

I'm surprised that no one has mentioned Corning's optical USB3.0 cable.

I did!

You're right. Totally overlooked it...

Notice me senpai!

[eliocor]

It seems to me that the Corning one is not a real insulator...
Power supply come from the optical cable (2 copper wires) and nowhere in the datasheet is reported the insulation value.
As blueskull wrote, you have to modify the cable to render it an insulator USB cable.

[electronic_eel]

I know this thread is a bit older, but it still comes up when you search for technical details of isolating USB.

I found one more isolation product: A USB 3.1 Gen 1 (SS with 5 GBit) Hub with isolation.

I found it sold under these names:

coolgear CG-U31iS4PH, https://www.coolgear.com/product/4-port-usb-3-gen1-isolated-hub-15kv-esd-surge-protection
Exsys EX-1182VIS, https://www.exsys.de/index.php?page=product&info=2062

The OEM developing & manufacturing these is most probably:
Comwise Tech MG-14346IS, http://35.222.228.198/usb-hubs/

When opening it, you see a quite interesting concept: isolating USB 2 (from Low Speed to High Speed / 480 MBit) is done differently than USB 3 Superspeed. USB 2 isolation is done with the Silanna ICE08USBC, similar as in the HifiMeDIY described above. USB 3 SS is isolated with ceramic coupling capacitors.

There is a regular GL3522 hub IC at the input. One of it's downstream ports goes to the isolation barrier, splitted by protocol as described above. This is most probably being done to buffer the USB 3 SS signals, to create a clean and known signal across the coupling capacitors. On the other side of the isolation barrier is another GL3522 hub, which connects the 4 downstream ports.

There is a Minmax MA01-05S05HI DC/DC voltage regulator on board. It provides 200 mA, just enough to power the hub itself, it is not designed for  onnecting bus powered peripherals. You can disconnect it with the jumper on the pcb. The DC/DC isolates 5.2 kV for 60 seconds. That translates to about 400 VDC permanent isolation, which is more than is offered on the data path, see below.

For bus powered peripherals you are supposed to connect an external 5 V power supply through a 5.5 / 2.1 mm barrel connector.

Finding details about the Silanna ICE08USBC is a bit difficult, as Silanna doesn't publish any datasheets. The best I could find is this presentation about their portfolio:
http://spacewire.esa.int/WG/SpaceWire/SpW-WG-Mtg17-Proceedings/Documents/Session 7 - SpaceWire Link Isolation (G.Baterina).pdf

On page 7 you can see how the IC is internally constructed. It seems to use capacitive coupling internally. So all claims about "optical isolation" you see in the Exsys datasheet are misguided.

On page 8 they claim isolation for 2.5 kVrms. Comwise Tech claims 3 kVrms in their datasheet. It could be that Silanna improved the isolation in the ICE08USBC, the presentation is from 2011 and they show the SIL11USBx which is probably a predecessor of the ICE08USBC. It could also be that Comwise Tech confused DC and AC rms.

Also they clearly state "Working voltage >100V". That means the 2.5 kVrms are just specified for a short period, usually 60 seconds. After that the isolation slowly begins to break down. The working voltage is what they consider safe for permanent usage. 100 V permanent matches what is commonly specified for DC/DC converters rated 2.5 kVrms @ 60 s.

The ceramic capacitors crossing the isolation barrier are 1812 size with 2 mm height. I measured them at about 1 nF. Several manufacturers offer such caps in X7R rated for 3 kVDC. I didn't find any for higher voltages in 2 mm height. So one can assume that they are rated for 3 kVDC. In the Datasheets they allowed for short-term overload to 120%, so no 3 kVrms. Also they warned not to use them for AC applications with continuously changing polarity.

The problem with capacitive coupling is that if the downstream side is floated to AC, a current starts to flow across the isolation barrier. With the voltages safe for permanent usage and a sinusoidial 50 Hz the current is in the µA range and doesn't matter much. But when using rectangular AC this can quickly become an issue and for example destroy the hub ICs because the data lines go outside their allowed common mode voltage.

There are no bulk capacitors anywhere on the pcb. The USB spec requires a minimum of 120 µF per downstream port, connected to the same net as the socket, after any protection measures. This is clearly missing. When plugging in a new device or when a device creates a current spike, the power for the 3 other ports or the hub IC can droop. This could be fixed by modding the board and soldering some polymer caps in the right places.

It seems like there are ESD protection ICs, the MSOP-8s labeled "118 6yUHG". I couldn't find a product name or datasheet with this marking. The SOT23-5 near the downstream ports are most probably short circuit protection ICs.

I did some USB data transfer measurements: transfer with USB 2 HS was a little bit slower (336 MBit/s) than directly connected to the PC (352 MBit/s). But this is very similar to what I measure on all my other hubs, so probably more related to having a hub in between at all than this specific hub. I couldn't measure a difference in latency, as USB latency tends to be hard to measure precisely. These measurements were done with the "benchmark" applet of Glasgow revC1 (Cypress FX2 + FPGA) https://github.com/GlasgowEmbedded/Glasgow.

I do not have a device to constantly saturate a USB 3 SS link. So for USB 3 SS I just did stability and data integrity tests, as I've also had USB 3 hubs which had connection problems under load. I wrote and read back 1 TB without disconnect or a data error.

Final Verdict:

Good:
- Isolated USB up to 5 GBit/s, no shortfalls with USB LS, FS and HS
- Ready-to-buy solution
- Convenient to use as it directly provides 4 ports and a power plug
- Solid construction
- ESD protection

Bad:
- Permanent voltage allowed across the isolation just about 100 VDC, so not suitable for connecting USB instruments floating on mains levels
- Capacitive coupling precludes some usage cases with AC
- No bulk capacitance on downstream ports as mandated by USB spec
- Costs about 200 EUR

[electronic_eel]

One more pcb photo which didn't fit in the previous post.

Also a copy of the Silanna pdf presentation linked above, just in case the they remove it.

[ajb]

For an interesting but waaaaaaaay overkill solution, PCIE over fiber extenders exist: https://adnacom.com/pcie/

Totally ridiculous for USB isolation, but could be a good solution if you needed to isolate some sort of PCIE expansion card interface.

[electronic_eel]

For an interesting but waaaaaaaay overkill solution, PCIE over fiber extenders exist: https://adnacom.com/pcie/

It is indeed way overkill for a USB solution, but I think the pricing of $575USD for the Adnaco-S1B is quite reasonable for what they do and how custom this solution is. When seeing the pictures on the overview page, I expected prices in the middle 4 digit region.

[electronic_eel]

To complete my evaluation of USB 3 capable isolation solutions, I also bought the 10 m version of the aforementioned Corning optical cable.
As mentioned above, this is not intended as isolation solution, but as a USB 3 SS (5 GBit/s) range extender up to 50 m. The cable contains two optical fibers and 2 thin copper wires for power supply. You have to open the cable and cut the copper wires to get isolation.

The cable is overmolded with a quite rigid rubbery plastic, probably some kind of polyurethane. Opening this to get at the power wires without destroying the optical fibres isn't easy. I tried different methods and found that using a sharp medical scalpel and scraping off small flakes of the plastic works best. Once you hit the wires you can carefully try to pry them off the plastic that encloses them. The optical fibres are surrounded by yellow protection fibres. Try to disturbe them as little as possible.

Once you freed the wires on a length of about 1 cm, cut the wires at the host side. Solder wires leading to a power connector to the device side. Isolate the joints with heat shrink tube. The plastic provided mechanical support and protection for the fibres. This is now mostly gone on the centimeter we opened. We have to add back something similar to make sure the fibres don't break. I used thick self sealing tape and wound it around the "wound" and my new power wires. I managed to keep my wire working, but when seeing the yellow protection around the fibres it felt like a close call. There is definitively a risk to destroy the cable.

The blue wire carries +15 V, the turquoise one ground. It seems they use a stepup to increase the voltage to 15 V, probably to minimize losses over the full 50 m they offer. But this is just for powering the device end of the cable, it is not intended for bus powered devices. When plugging in the cable, the current draw of the device end is a little bit under 100 mA at 15 V. This quickly drops to about 30 mA when idle.

So for a bus powered device you also need a hub, power supply for the hub and 15 V for the device end of the cable.

The host and device ends of the cable look like they are glued together and opening will break them. As my cable survived the isolation surgery, I didn't want to risk that.

The cable presents itself on the USB as two Hitachi hubs (one USB 3 and one USB 2) and a "Corning Optical USB V1.1" device, see attached lsusb output. Devices attached to the cable show up below the respective hub. I successfully tested devices with USB Fullspeed (12 MBit), Highspeed (480 MBit) and Superspeed (5 GBit). I also tried to plug it into a USB 2 socket on my pc and then the devices were just using up to 480 MBit connections. This leads me to believe that they implemented this properly with a distinction between USB 2 and 3 and not with a hack like a 2-to-3 transaction translator.

Transmission speeds were very similar to what I got with the Exsys hub presented above. Also the transmission with USB 3 SS was stable for 1 TB.

I don't know why they implemented the cable this way. It seems they were completely focused, like wearing blinkers, on a small and thin consumer  solution to extend USB 3. Why didn't they split this into two small boxes that are connected with regular OM3 fibre over LC connectors, the device side powered with a small 5 V wall wart? Then you don't need different products for different lengths, the user would just buy matching pre-made fibre patch cables which are common. Isolation would have been covered too and you could also use it with a fibre installation in a office building.

Final Verdict:

Good:
- Isolated USB up to 5 GBit/s, no shortfalls with USB LS, FS and HS
- Fibre optics provide stable and safe isolation for very high voltages, permanent mains voltage is no problem
- Very low capacitive coupling allows to float the device side to AC

Bad:
- No ready-to-buy isolation, wire surgery necessary for isolation
- Risk of damaging the fibres
- Limited mechanical stability where the wires were cut
- Costs about 150 EUR
- Hub, power for the hub and 15 V for the device end of the cable not included

[MT]

So can a debugger like STM32 Nucleo/Disco be on a WIFI router or will the router not recognize the device?
I do not have WIFI router.