DIY USB isolator keeps connecting and disconnecting devices

Thread Starter

Vilius_Zalenas

Joined Jul 24, 2022
129
Hi,

Recently I designed and made a USB 1.1 Isolator using a ISOUSB111 chip. I designed the PCB with up to 2 amps on the isolated output, hence adding some additional power components, but that doesnt really matter. As soon as I connect any USB device to my computer, it starts to show that some device is constantly being connected and disconnected (over and over again.) I checked for shorts (there were none), I am getting 5V on the output, what could possibly be wrong? I know that USB 1.1 is really forgiving, but I routed a proper differential pair of 90 Ohm with a solid ground plane under the data lines (my PCB is only 2 layers, so the data lines look so wide), is there any chance my problem is related to some EMI issue (if thats even the case with USB 1.1?) Thank you for any advice.
 

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ericgibbs

Joined Jan 29, 2010
17,981
hi,
No, I was trying to advise you of an available applications datasheet, that is why I attached a copy for you, to my post.
E
 

Thread Starter

Vilius_Zalenas

Joined Jul 24, 2022
129
Have you checked the current draw? The computer may be cutting power if the load is too high.
I have 500 Ohm load across the output at all times (this is required to maintain the LDO stability.) However, I tried sticking a USB flash drive and an SD card (they work fine without the isolator), but I got the same result, I guess currents are not the problem here...
 

Thread Starter

Vilius_Zalenas

Joined Jul 24, 2022
129
hi,
No, I was trying to advise you of an available applications datasheet, that is why I attached a copy for you, to my post.
E
Alright, I found the trick, I would have to plug both USB inputs (both USB ports, because one is designed only for the additional power) My transformer drivers are constantly on, so even is my SD card draws microamps, I have to feed a solid 2A to the transformers, everything seems right according to the design.
 
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