I am running the stm32f407 at 1.85V and was wondering if it would be possible to get USB working at this operating voltage. I've pulled up the d+ line to Vbus but cannot get proper enumeration. I believe as long as the differential signal is 100-200mV on the receiving side it should still work. Even with a very short USB cable still no enumeration. Is some kind of level translator or usb signal repeater my only option? Thanks.