[sdiy] How to design out "usb noise"?

[brianw]

On Feb 4, 2024, at 5:19 PM, Eric Brombaugh wrote:
> Not optical, but it is a USB isolator:
> 
> https://www.analog.com/en/products/adum3160.html

Very cool - monolithic air core transformers - those will work bidirectionally.

I had the ADuM4160 data sheet in my collection. I recall seeing the transformer coupling.

One challenge I see is that USB requires a Device to stay off D-/D+ until VBUS is detected. This is usually implemented in firmware by connecting a GPIO that detects when VBUS exceeds some threshold. The firmware keeps the USB port inactive until it sees VBUS "on" - I couldn't find any support for this in the ADuM3160, so I assume you'd need some sort of isolation when feeding that GPIO from the other side of the isolator. Probably not that difficult, but I'm surprised they didn't just add a pin for that, with isolation to make it convenient for designers.


> https://www.ti.com/product/ISOUSB211
> 
> You can even buy similar stuff cheap:
> 
> https://www.amazon.com/HiLetgo-ADUM3160-Voltage-Isolator-Support/dp/B07235PR4V/ref=sr_1_2_sspa

I was going to suggest that this is probably cheap because it doesn't support High Speed, but then I noticed that the Analog Devices part doesn't support High Speed, either. The Texas Instruments isolator does handle High Speed (although the USB-MIDI spec doesn't mention High Speed, so it's probably moot).

Brian


> On 2/4/24 17:44, brianw wrote:
>> If there is a chip that optically isolates the bidirectional
>> differential USB Data lines, I'd be fascinated to look at a data sheet
>> to see how it works.