STM32U5 VDDUSB consumption

[FNiel.1]

Hi, We are designing a low power design using STM32U5A9NJH6Q. As it is low power we aim for lowest possible consumption.

We are not using USB on the device; hence we would like to omit any consumption from the VDDUSB and would have connected it to VSS if there where not stated this in the DS: 

"

• VDDUSB = 3.0 V to 3.6 V
VDDUSB is the external independent power supply for USB transceivers. VDDUSB
voltage level is independent from the VDD voltage and must be connected to VDD or
VSS pin (preferably to VDD) when the USB is not used.

"

Now our VDD is 1.8V and although it states 3-3.6V then we do assume that this range is only needed if the USB interface shall be operational, as it has been the case with other STM32s.

The tricky point is the "preferably to VDD".

So the question is what is consumption if connected to our 1.8V and what is the impact if connecting to VSS?

[FNiel.1]

We were hoping to get some answers to this item, as we are in the middle of implementation.

[FBL]

Hi @FNiel.1 

When USB is not used, you should connect VDDUSB to VDD = 1.8V and VDD11USB to VDD11 either when supplied in LDO or in SMPS. Actually, most of the current used by the USB is not coming from VDD11USB but from VDDUSB power supply.

Check this FAQ. FAQ: Configuring the VDD50USB and VDD33USB pins on... - STMicroelectronics Community This should be applicable to STM32U5A9xx as well.