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niconiconi

After closer inspection, it turned out that the astonishing 1500 volts (AC) & 2100 volts (DC) "Maximum Isolation Working Voltage" boasted by Texas Instruments is only an industry standard for digital isolation *components*, while authentic, it's not for complete *systems*.

When you actually use the system-level safety standards used by national regulators like IEC 60950 and IEC 60664, you'll find in a real application, the 8 mm creepage distance at the chip package limits the working voltage to no more than 800 volts AC (Material Group 1, Pollution Degree 2, Reinforced Insulation). So much for the marketing.

> The large print giveth and the small print taketh away. -Tom Waits

> The nice thing about standards is that you have so many to choose from; furthermore, if you do not like any of them, you can just wait for next year's model. - Andrew S. Tanenbaum

#electronics #usb

28 Dec 2021 at 16:26 | Open on cybre.space
7 comments
niconiconi replied to niconiconi

There are more gotchas.

> Clearance: 8 mm
> Care must be taken during board design so that the mounting pads of the isolator on the printed-circuit board (PCB) do not reduce creepage and clearance.

Then the 8 mm clearance is immediately violated, officially, in the recommended footprint at the end of the datasheet. #electronics #usb

28 Dec 2021 at 16:37 | Open on cybre.space
niconiconi replied to niconiconi

Another pitfall is the IPC-2221 standard in most PCB calculators. Its clearance requirement can get ridiculous for some use cases because of the stepwise definition, yet insufficient for other uses cases (reinforced insulation).

"Friendship ended with IPC-2221, now IEC 60950 is my best friend!" #electronics

28 Dec 2021 at 17:12 | Open on cybre.space
niconiconi replied to niconiconi

UL sucks too. Their Recognized Component certificates are essentially useless. All they tell you is a certification exists, but without any information about the rated working conditions, which are critical to safety. A vendor can say its power supply works up to 1000 volts, and claims the power supply is also UL certified (without telling you it's certified only for 100 volts, the 1000 volts spec is only a functional rating and cannot be used for safety-critical applications).

The real information is in UL's Conditions of Acceptability, and it's often nowhere to be found. You can either try asking the vendor nicely and hope they don't ignore your request. Or pay (possibly thousands of dollars?) to purchase that information from UL. ledsmagazine.com/company-newsf #electronics

UL sucks too. Their Recognized Component certificates are essentially useless. All they tell you is a certification exists, but without any information about the rated working conditions, which are critical to safety. A vendor can say its power supply works up to 1000 volts, and claims the power supply is also UL certified (without telling you it's certified only for 100 volts, the 1000 volts spec is only a functional rating and cannot be used for safety-critical applications).

29 Dec 2021 at 17:18 | Open on cybre.space
niconiconi replied to niconiconi

PCB ordered. Added common-mode chokes at both sides of the isolated converter hopefully to suppress some noise across the barrier. Also removed the slot - the SIP DCDC module only has functional isolation, so increasing the creepage distance further is pointless... #electronics

USB isolator board. The board is symmetrically laid out, left is the host side, right is the device side, with an isolation barrier in between.
Back side of the PCB. A few SMD capacitors and resistors. And a "Let's All Love Lain" on the silkscreen.
31 Dec 2021 at 15:48 | Open on cybre.space
niconiconi replied to niconiconi

Hopefully I won't accidentally kill myself later in the dielectric withstand voltage test by the 3000 volts HiPot tester. LIke many on the Fediverse, ihatebeinga.live is a thing, but a HiPot tester is just a terrible way to die. #electronics

DANGER DO NOT TOUCH Not only will this kill you, it will hurt the whole time you are dying.
31 Dec 2021 at 15:56 | Open on cybre.space
niconiconi replied to niconiconi

My USB 2.0 isolation board is working. The Texas Instruments chip ISOUSB211 works as advertised, it really is the first USB 2.0 high-speed (480 Mbps) galvanic isolation chip on the open market. I'll release all the design files tomorrow. #electronics #usb

USB isolator board. The board is symmetrically laid out, left is the host side, right is the device side, with an isolation barrier in between. Across the barrier is a Texas Instruments ISOUSB211 isolated USB repeater chip, and also a DCDC power converter module.
Benchmark result using a USB flash drive. The read speed is 45 MiB/s, or 360 Mbps, this speed implies the isolator is working properly in high-speed USB mode.
6 Jan 2022 at 15:22 | Open on cybre.space
niconiconi replied to niconiconi

TI ISOUSB211 development board design is now public. This TI chip is the first ASIC capable of doing USB 2.0 High-Speed (480 Mbps, not 12 Mbps) galvanic isolation on the open market. As always, #Lain must be loved. notabug.org/niconiconi/isousb2 #electronics #usb

USB isolator board. The board is symmetrically laid out, left is the host side, right is the device side, with an isolation barrier in between. Across the barrier is a Texas Instruments ISOUSB211 isolated USB repeater chip, and also a DCDC power converter module.
Back side of the PCB, there are only a few resistors and capacitors on this side. On the silkscreen there's a sketch image of Lain, with the words "Let's all love Lain"
7 Jan 2022 at 7:40 | Open on cybre.space
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