VDD33USB connection problem when not using USB

[AndersonKKK]

Hi,

I do not plan to use USB, and the STM32N6's VDD is 1.8V.

However, creating a new 3.3V power supply just only for the VDD33USB pin is too inefficient.

The datasheet lists the absolute maximum ratings for VDD33USB as ranging from 0V to 3.6V when USB is not used, and the comment below states the following:

1. All main power and ground pins must always be connected to the external power supply, in the permitted range.

Therefore, Finally if I do not plan to use USB on the STM32N6, which of the following options should I choose for the VDD33USB pin?
(have to consider leakage current in stop mode)

1) NC
2) 3.3V (by creating a new power supply)
3) 1.8V
4) GND

thanks in advance.

[TDK]

If you're not using USB, you can ground VDD33USB.

You may want to tie it to VDD instead if you need margin on the UCPD pins. But if everything coming in is 1.8 V, no issues with grounding it.

[FBL · Accepted solution]

Hi @AndersonKKK 

With all external interfaces at 1.8 V, since you are not using USB, you can safely tie VDD33USB to GND to minimize leakage and avoid generating 3.3 V.