Author Topic: High-speed USB isolator (Read 54162 times)

cybergibbons · « **on:** July 24, 2011, 01:04:29 pm »

I've had a few mishaps now where I have blown up a USB port on a desktop machine and written off a monitor with a built in USB hub before now. I have a lot of bare circuit boards with USB interfaces and a number of pieces of test equipment (Bus Pirate, Open Bench Logic Sniffer, Saleae Logic, Scope, RS232 adapter, FTDI cable, GoodFET...) so it is only a matter of time before something untoward goes down a USB cable.

There are USB isolators available, but they are only full speed (12Mbps):
http://www.olimex.com/dev/usb-iso.html
http://www.bb-europe.com/product_family.asp?FamilyId=651&Trail=168&TrailType=Main

And there are also hubs available, but all seem to be full speed, not high speed.

I'm not sure how much protection I really need or want. Worst case really is going to be 60V at 3A from my bench power supply.

Any ideas?

ejeffrey · « **Reply #1 on:** July 24, 2011, 01:26:19 pm »

I have seen high speed isolators but they are pretty expensive. They might end up being more expensive than the equipment you want to protect...

Since you basically just want to protect equipment, not provide a safety isolation barrier you might get away with just using a cheap hub. It won't protect against everything, but it might die first and save whatever it is connected to. Since most USB hubs are powered via an isolated DC-DC converter, you should run a separate grounding wire to provide a ground path for any overvoltage. Just get an extra USB cable, cut off the 'A' end, and solder a grounding wire to the shield. Then plug it into your hub.

You could also roll your own passive surge suppressor device. A usb B to A pass-through box with TVS diodes on each wire should do the trick.

onemilimeter · « **Reply #2 on:** July 25, 2011, 02:29:23 pm »

May be those product uses this IC:
http://www.analog.com/en/interface/digital-isolators/adum3160/products/product.html

Examples of high-speed USB isolator in the market?

mikeselectricstuff · « **Reply #3 on:** July 25, 2011, 03:56:20 pm »

I found this - doubtless very expensive...
http://www.baaske.net/usb2_galvanisch_trennen.html?&L=1

The problem is there aren't many isolation devices that will run at the 480mbits/sec full speed. You're probably limited to either multiple isolators in a parallel bus, or laser based fibre-optics as used in the above product. I wonder if you could do something with gigabit ethernet magnetics.
You then have some very high speed logic to deal with as well, and the market is small, so it's never going to be cheap.

However if all you want is protection it should't be hard to make a pretty bulletproof protection circuit - low-capacitance TVSs, and maybe polyfuses to protect the TVSs against sustained DC.

ejeffrey · « **Reply #4 on:** July 25, 2011, 04:07:38 pm »

I just looked at the ones we have in our lab. I thought they were high-speed compatible, but they are only full/low speed.

I suspect one problem here is that the signaling voltages and line termination are different between 1.5/12 Mbit and 480 Mbit, and uses a variety of pull-up/pull-down resistor switching tricks to negotiate the speed in a backward compatible way. Making an isolator properly handle the negotiation on both ends for all possible configurations while being transparent to the host is probably more trouble than it is worth. Opto-isolation is most common in industrial environments, and the most common devices are simple serial devices for which even 1.5 Mbit is more than sufficient.

cybergibbons · « **Reply #5 on:** July 25, 2011, 05:24:59 pm »

As you say, the tricks used to get backwards compatibility along with such high speeds may be why they are so rare. The cheapest option is probably just to have a computer that I accept is going to get damaged and not have any data on it that I really need!

The full speed isolator will probably do for some equipment - I think a lot of things report high speed but run at much reduced speed. The Saleae Logic is probably the only thing that needs to run at high speeds.

Time · « **Reply #6 on:** July 25, 2011, 06:20:06 pm »

Look into the Analog Device I-couple technology. They make some cheap and good high speed isolators based around aircore pulse transformers.
http://www.analog.com/en/interface/digital-isolators/products/index.html#Standard_Isolators

http://www.newark.com/analog-devices/adum1100arz/ic-digital-isolator-18ns-soic-8/dp/19M0749

Not sure if that helps or not. I am not familiar with USB so I am not sure if something like this would work.

onemilimeter · « **Reply #7 on:** July 25, 2011, 06:28:28 pm »

Quote from: Time on July 25, 2011, 06:20:06 pm

Look into the Analog Device I-couple technology. They make some cheap and good high speed isolators based around aircore pulse transformers. Well above the speeds of USB.

http://www.analog.com/en/interface/digital-isolators/products/index.html#Standard_Isolators

http://www.newark.com/analog-devices/adum1100arz/ic-digital-isolator-18ns-soic-8/dp/19M0749

Not sure if that helps or not. I am not familiar with USB so I am not sure if something like this would work.

Usually the isolator is unidirectional...

Time · « **Reply #8 on:** July 25, 2011, 06:33:29 pm »

Oh just noticed your post. Sorry about that.

mikeselectricstuff · « **Reply #9 on:** August 10, 2012, 10:34:02 pm »

http://www.icron.com/ make some hi-speed USB over cat5 and fibre interfaces. Not clear if the cat5 ones provide isolation.

jamesp15 · « **Reply #10 on:** August 10, 2012, 11:09:43 pm »

If its a desktop PC: What about using cheap PCI/PCIexpress USB adapters, if one blows you don't lose a motherboard.
Quite a few on ebay under $10 US.

David_AVD · « **Reply #11 on:** August 10, 2012, 11:10:13 pm »

Another danger in any connection to a PC (not just USB) is large currents flowing in the ground wire.

Using a PCI USB card on the PC and making a little box to put a 500mA fuse in series with all 4 wires would at least limit the damage.

T4P · « **Reply #12 on:** August 11, 2012, 04:08:15 am »

Best way is to use a powered USB hub, at least the motherboard ground wires from PCI doesn't go boom or the Southbridge
your computer might have polyfuses but that's not good of a idea

hans · « **Reply #13 on:** August 12, 2012, 06:31:20 pm »

At home I always use a $10 Sweex (I believe this is a local dutch el-cheapo brand) USB hub. Works fine, own power brick so it's (hopefully) not drawing any power from the PC to power the devices. This does have the consequence not being power limited I think, because I have blown 2A MOSFETs on my PICKIT2 before (bloody PICKIT software hang and accidently shorted the power output, smoke

)

If you want to 'isolate' a single USB port, you may find it convenient getting an old laptop and use that. This of course brings issues if you have 2 USB devices, because USB on the laptop still has the same ground. And working on it from the 'workstation' isn't convenient.

This also stresses the disadvantage of high-speed USB devices on USB. Like a RS-232, bus pirate and low-bandwidth thing is probably something you can run on a hub plus 12mbit isolator. A scope or logic analyzer not. Laptop for 'debugging' via scope and such only? Futhermore, how big are the odds you need your logic and scope simultaneously? (scope: signal quality, logic: protocol debugging)
I don't think a PCI-e device will work though like james suggests. There is a chance they probably don't have any fuse and will probably blow the motherboard anyway. The device is powered from the motherboard after all.
I see on many modern motherboards polyfuses now. I paid close detail on when purchasing my last PC whether they contained them, but I actually couldn't find any motherboard without. Though, I did spent 170$ or so on my MB, so I guess it *should* have some protection.

What exactly have you blown? I also played with projects at internship and college with USB. This is ofcourse on a laptop (Samsung R510 AS02) and not in my own hobby space. I shorted out the +5V to pretty much anything whilst completely messing up (and messing up the fixes!) the pin-out of an USB B connector, and the only damage I did was to my projects. All 3 ports still work.

That experience gave me so much trust in this laptop I'm not afraid of blowing it up.. At internship I didn't have the right cable for an industrial USB boxed header connector (like onboard of a MB). So I disassembled one and directly connected the crimps on the headers, with no connector.. A fellow intern, which is a bit more sloppy with everything, was a bit nervous seeing that. He said that if he would do that, he would always short something out and kill it. Worked great for the few things I had to (re)configure over USB

NiHaoMike · « **Reply #14 on:** August 12, 2012, 07:02:56 pm »

I have an IOGear wireless USB hub that I got on sale for $20 or so. Range isn't too good, but it works perfectly for isolation.

The difficult part of isolating USB 2 is because the data lines are bidirectional. The interesting part is that isolating USB 3 would actually be quite easy for anyone experienced in high frequency design, because the two USB 3 pairs are unidirectional. It might be as easy as wiring the lines to a pair of fiber transceivers. It might also be possible to use transformers since USB 3 is AC coupled, but I'll have to check the frequency range.

If possible, isolate the connection where it's easy to do so.

Icchan · « **Reply #15 on:** September 19, 2015, 12:49:27 pm »

I've come up against this issue too.

I was planning to use an high spec USB audio interface for signal analyzing and spectrum analyzing, and I'm worried about the USB power quality messing up the specs for the interface. Not to mention to prevent me blowing stuff up.

Might not be an issue if I research and test it further, but it's really hard to find anything below 300€ for isolating USB 2.0 high speed connection.

Surprising since I wouldn't think it would be that hard to do :/

NiHaoMike · « **Reply #16 on:** September 19, 2015, 03:54:41 pm »

Quote from: Icchan on September 19, 2015, 12:49:27 pm

I've come up against this issue too.

I was planning to use an high spec USB audio interface for signal analyzing and spectrum analyzing, and I'm worried about the USB power quality messing up the specs for the interface. Not to mention to prevent me blowing stuff up.

Might not be an issue if I research and test it further, but it's really hard to find anything below 300€ for isolating USB 2.0 high speed connection.

Surprising since I wouldn't think it would be that hard to do :/

Convert the USB to I2S or S/PDIF and then isolation is easy or trivial.

C · « **Reply #17 on:** September 19, 2015, 05:58:54 pm »

USB-3
Could be wrong, but my quick read of USB3 is that it is USB2
They just added two unidirectional differential pairs. and extra packet types to control the two channels.

USB-3 = USB2 + two unidirectional differential pairs.

C

NiHaoMike · « **Reply #18 on:** September 19, 2015, 07:24:28 pm »

Quote from: C on September 19, 2015, 05:58:54 pm

USB-3
Could be wrong, but my quick read of USB3 is that it is USB2
They just added two unidirectional differential pairs. and extra packet types to control the two channels.

USB-3 = USB2 + two unidirectional differential pairs.

C

USB 3.0 will work with the USB 2.0 pair disconnected. Not sure about USB 3.1.

C · « **Reply #19 on:** September 19, 2015, 10:26:16 pm »

Thank you NiHaoMike
I did did not see that, nice to know.
Did you see any difference with 2.0 pair disconnected?

C

Howardlong · « **Reply #20 on:** September 20, 2015, 04:20:37 pm »

Two other options...

I have a Belkin (gag) Network USB Hub F5L009 v2 from a few years back. I am sure other makes are available. This is not just a physical layer CAT 5 thingy, it tunnels USB over IP. This will be isolated as it'll go over Ethernet magnetics.

The other option might be the almost forgotten wireless USB technology based on UWB. I have a Q-Waves USB to HDMI adapter from about five or six years ago, they also have a wireless USB to USB adapter (http://www.amazon.co.uk/Q-Waves-Wireless-USB-Data-Kit/dp/B002T9VBVM/ref=cm_cr_pr_product_top?ie=UTF8) currently deeply discounted to £15. There might be a reason for that though, not sure what the driver situation is for these devices.

Stonent · « **Reply #21 on:** September 20, 2015, 05:50:47 pm »

Quote from: mikeselectricstuff on August 10, 2012, 10:34:02 pm

http://www.icron.com/ make some hi-speed USB over cat5 and fibre interfaces. Not clear if the cat5 ones provide isolation.

We've used the Icron fiber devices where I work. I would recommend using an add-on wall-wart rather than the USB port to power the device as we've had them cut out when the load gets too much.

Since the fiber ones use standard multi-mode SFP modules, they are easily serviceable. I would be reasonably sure that the cat5 version uses the same mag jacks as you would normally use for Ethernet.

I've used some of these before: http://trinetusa.com/products/usb-2-plug-play-utp-extender-1to1/
It uses standard Ethernet to transmit the data, the computer end of the device is just a USB to Ethernet device and will function as so if you load the chipset manufacturer's drivers.
To use the USB over Ethernet functionality, you need to install the software that comes with it that creates some kind of tunnel. You can even sniff the traffic using a packet sniffer and it's just all TCP/IP traffic.

The PC side uses an ASIX USB to Ethernet chipset and uses an Ethernet mag jack, so it would give you whatever isolation level that a mag jack can do.

wreeve · « **Reply #22 on:** September 20, 2015, 06:29:32 pm »

I've used the USB 2.0 Isolator from www.electronics-shop.dk a few times in lab environments where the chassis connections of USB connectors can corrode causing GND loops if you are not careful! USB seems to hate GND loops!

wraper · « **Reply #23 on:** September 20, 2015, 06:33:13 pm »

Quote from: wreeve on September 20, 2015, 06:29:32 pm

I've used the USB 2.0 Isolator from www.electronics-shop.dk a few times in lab environments where the chassis connections of USB connectors can corrode causing GND loops if you are not careful! USB seems to hate GND loops!

But it's full speed only = 12 Mbps

Stonent · « **Reply #24 on:** September 20, 2015, 09:03:49 pm »

Quote from: wraper on September 20, 2015, 06:33:13 pm

Quote from: wreeve on September 20, 2015, 06:29:32 pm
I've used the USB 2.0 Isolator from www.electronics-shop.dk a few times in lab environments where the chassis connections of USB connectors can corrode causing GND loops if you are not careful! USB seems to hate GND loops!
But it's full speed only = 12 Mbps

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

Quote

Description:
Extends an USB 2.0 signals up to 100 meter/ 330 ft using one Cat5e/6 UTP cable.
This extender supports USB 2.0 device at speed up to 480 Mbps.
Specification:
(INPUT)
USB A type JACK
USB Input
RJ45
R042-EXT-C5E
UTP EXTENDER
Remote Unit
R042-EXT-C5E
USB 2.0 UTP Extender
Remote Unit
• Extends transmission distance up to 100 meter / 330 feet
• USB 2.0 compatible
• AC/DC 5V 2A power adapter included
• Supports speed up to 480 Mbps
• Ideal for USB peripherals extension, industrial control, security, digital signage
• Works with Windows XP, Vista, Windows 7


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Author Topic: High-speed USB isolator (Read 54162 times)

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