thank you for your help investigating this issue.
At issue state, both LED13 and LED14 are ON with green color.
On my system (Evaluation Board + VF61 module), when I connect external 3.3V to SODIMM 30 the issue happens 100% of the times. But the external voltage is applied directly to the pin of module.
With USB cable, the issue happens sometimes, and sometimes it doesn’t; on your system the issue doesn’t happen.
Looking to the chematics of Evaluation Board, the USB 5V is reduced to 3.3V through a R73=560R and R74=1k. Maybe 560R is near the limit where the issue happens or not.
Could you see the issue if you reduce R73 and R74 to 280R and 500R, for example?
On the use cases:
- on the evaluation board I connect directly a waveform generator to SODIMM 30; on the real case I have an external device (which can bring voltage even if VF61 is powered off), but the imput circuit is protected. No direct connection to the pin, so I think this is not a real danger
- USB OTG is a real case because I want to see my VF61 device as mass storage when I connect it to a PC and I want to download data from VF61 device to a mass storage device.
If you can reproduce the issue, you can investigate and suggest different design circuit (if needed).