Using USB FS with STM32F412REY6TR at 1.8VDC

[bwefers]

Reading through the initial datasheet for this part I thought we could get away with using the USB_FS_VBUS as the VDDUSB pin as I didn't see a dedicated pin for the VBUS. It is now becoming apparent that this was misguided. Are there anyways to bring up the USB features of this chip at voltages below 2.7VDC? I have attached the relevant schematics below. 

On the board I have access to 5V vbus, 3.8V and 1.8V. We brought down all IO voltages to 1.8V to get away from having to use a level shifter to talk with the AFE. 

[STOne-32 · Accepted solution]

Dear @bwefers ,

This is not possible for this MCU , as our Internal Full speed PHY  for USB is not designed to work at 1,8Volts . It is more at PHY and Analog side for D+ and D- , not at Digital and core side . 

On STM32F446 this is possible with dedicated VDDUSB Rail for the embedded PHY .

STOne-32