Would like to use a STM32L452 MCU with VDD=1.8V but still be able to maintain USB functionality for DFU updates. This device has a separate VDDUSB pin that I would like to power separately (3.3V) from an LDO when VBUS is connected.

[JOkam.1]

As long as the VDDUSB supply is from 3.0V to 3.6V and is the last to be applied and first removed (vs. VDD), there should be no issues?

[Bruno_ST]

Hello @JOkam.1​ 

Yes, according to datasheet 3.9.1 Power supply schemes, VDDUSB = 3.0 to 3.6 V: external independent power supply for USB transceivers. The VDDUSB voltage level is independent from the VDD voltage.

Concerning Power-up/down sequence in this same chapter, check that you meet the requirements on VDD & VDDA (no contraints on VDDUSB).

BR,

Bruno

[JOkam.1]

Thank you for the clarification.