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Usb ground loop isolator1/21/2024 This year I've considered, tested (and am still testing) a few ASIC solutions for 480 Mbps USB galvanic isolation, and I plan to write a detailed article about it, but here's a quick summary. Safety-related certifications: – 8000-VPK VIOTM and 2121-VPK VIORM (Reinforced and Basic Options) per DIN VDE V 0884-11 – 5700-VRMS isolation for 1 minute per UL 1577 – IEC 62368-1, IEC 60601-1 and IEC 61010-1 certifications – CQC, TUV and CSA certifications – All certifications planned.Ambient temperature range: –40☌ to +120☌.Meets CISPR32 class B emissions limits. ![]() VBUS voltage range: 4.25 V to 5.5 V – 3.3 V and 1.8 V internal LDOs.Programmable equalization to compensate board trace loss in high speed mode.Automatic speed and connection detection.Supports low speed (1.5 Mbps), full speed (12 Mbps) and high speed (480 Mbps) signaling.USB2 ISOUSB211 High/Full/Low Speed Isolated USB Repeater, now in pre-production : 1 Features This is also why most 3D printers are not connected to your PC via USB so you could control them directly from software (and disconnect the USB after "uploading" the files to an SD card), and instead you have to use a physical SD card to transfer the files.) These controllers almost always share motor ground with logic ground, you see. ![]() (Similar ground loop and noise issues occur with 3D printer and other robotics controller boards, if connected to a PC via USB. Keep traces short and according to the datasheet, use the recommended passives, and it will Just Work. If it matters any, putting an ADuM3160 to your own design in externally provided devices, is similarly trivial. This supply is not isolated from the device, it is directly provided, so you do need to use an isolated AC-DC supply. The Olimex one has one very useful additional feature: you can use an isolated DC supply, 8 - 15 VDC, to supply up to 750mA at 5VDC to the device. There is nothing to cut out to reduce price, so as long as those two components are legitimate, and the board itself looks okay (not a reject or something), they really are acceptable for the task here. They really are very simple devices, with just a few passives (resistors and capacitors) in addition to the ADuM3160 and DC-DC isolator parts. ![]() The ones I got off eBay do have nice isolation, BTW, typically 1 kV (due to the cheaper DC-DC converters used). Technically, USB is supposed to handle even VUSB-GND shorts indefinitely, but spending 8-18€ for an isolator to be certain was a no-brainer to me. I personally don't need the isolator to break ground loops, but to protect my more expensive hardware from my butterfingery when I experiment with microcontrollers. (These all have native USB, and not an USB-to-serial converter like most Arduinos have.) Using Teensies and ATmega32u4 Pro Micro clones (with Arduino Leonardo boot loaders), I get the same ~ 1 Mbyte/sec transfer rate over the isolator as I do without. ![]() These do limit the speed, and high-speed USB (480 MBit/s) wont work – or rather, they work, but will be limited to 12 MBit/s. In theory, USB should be tolerant of even shorting USB 5V to ground, but with my luck, I'd manage to release the Magic Smoke without the isolator somehow.) Do note that the ADuM3160-based ones typically have a dip switch selecting 1 MBit/s (low-speed USB) and 12 MBit/s (full-speed USB) I always use mine in the 12 MBit/s mode. (Whenever I poke around with the connections on my microcontrollers, I use an isolator as a final safety measure against my own butterfingery. Personally, I just checked the DC-DC converter on my cheapies when I bought them, and verified they are isolated DC-DC converters (and they were), and they seem to work absolutely fine for me. The ADuM3160 datasheet is short and the circuit really is very simple, and the CN0373 reference design (lower left corner of figure 1) shows you really only have a couple of resistors (24 Ohm 1% for 12 Mbit/s operation, none for 1 Mbit/s) and a couple of capacitors, and maybe a ferrite bead plus whatever circuitry you need for the isolated 5V-5V DC-DC conversion. In Europe, the Olimex USB-ISO is a viable option too. I would not expect more than 350mA (while drawing max. They are direct implementations of the datasheet, and only the isolated DC-DC converter on them varies (providing isolated 5V from the host computer) they also typically provide less power than they draw from the host (due to losses). I regularly use cheap eBay ADuM3160-based isolators with Arduino-compatible microcontrollers.
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