I had shared that my ADUM3160 USB isolator dongle does a reasonable job at not only isolating a 12Mbit USB connection, but also at providing an isolated supply. The widget I purchased was distributed by seeedstudio and looks identical to their marketing images.
The widget
https://www.seeedstudio.com/USB-Isolator-p-4098.html
Any self-powered USB device that is in need of a low-noise supply is going to filter and regulate the incoming USB supply voltage. So, measuring the noise post a jellybean linear regulator, like the LM317, gives a ball-park estimate on what a USB device might experience as a result of the isolated supply module.
My test load has a 60 Ohm load on the input (120R||120R) and a jellybean LM317 configured for a 3 V output with a quality MLCC on the input/output.
I don’t really want to tear my widget apart just to find the PN of the DCDC isolation module, so it will remain a mystery. There are hundreds of 1W DCDC isolation modules available, most seem be based on a Royer oscillator and not contain a dedicated push-pull driver IC. Take for example the flex power module
https://flexpowermodules.com/resources/fpm-techspec-pua-a
My isolation dongle is switching at 362 kHz, similar to a SN6501 (or eqv).
My test coupon is powered via the front-panel USB connector on my o-scope. I measured the output noise of the LM317 with and without the USB isolator dongle inline.
There is minimum impact from audio frequencies to 20 MHz.
During the deadtime of the push-pull driver a resonance of ~90 MHz is observed which generates differential/common-mode HF noise. With better layout and filtering this could be improved.
The newest kid on the block for push-pull drivers appears to be the NXP NXF6501, which has slew rate control and spread spectrum clocking.
https://assets.nexperia.com/documents/data-sheet/NXF6501_Q100.pdf
https://assets.nexperia.com/documents/data-sheet/NXF6505_Q100.pdf
This isolation widget adds a negligible amount of PARD below 20 MHz. Any widget designed to operate on USB power will have filtered and conditioned the incoming USB supply voltage for any low noise application.
If you want an ultra-low-noise supply, you will have to design your own.
If you know the PN of the isolation module, I would be interested to know.
Aside, there is an open-source clone here: https://github.com/wagiminator/ADuM3160-USB-Isolator
