STM32L412 VDDUSB Disconnect

[JHong.1]

I am using STM32L412RB for a low power application.

VDD: 1.8V

I have a 3.3V regulator that I would like to only turn on when I am using USB.

According to the datasheet (https://www.st.com/resource/en/datasheet/stm32l412kb.pdf pg 19), VDDUSB = 3.0 to 3.6 V. It doesn't say much about whether I can have it floating when not using USB.

Is floating VDDUSB pin acceptable when not using USB? VDDUSB will be powered when I use USB.

Thank you

[waclawek.jan]

Look up the VDDUSB's range in the datasheet - it starts at 0V when USB is not used. That IMO means that yes, you can leave the pin floating.

Note the requirement for VDDUSB (and all other VDDs) to be below VDD when the mcu starts up.

JW