USB Host: How to power VBUS?

Lars Beiderbecke · ‎2020-01-20

I'd like to implement a USB host on my STM32F7x3 so that I can connect a USB mouse to it. I'm somewhat confused about VBUS, though.

This is the respective diagram in the AN4879 USB Hardware Guide:

According to the description, the box "Current limiter power switch" could be a STMPS2151STR. This IC, however, cannot transform 3V3 to 5V, as the diagram suggests.

Is it crucial that VBUS is connected (via current limiter power switch) to one of the STM32 pins, or could I use 5V instead? Do I need to connect VBUS to the STM32 in order to detect that a device is connected? If so, how do I bridge the voltage gap?

waclawek.jan · ‎2020-01-20

> Is it crucial that VBUS is connected (via current limiter power switch) to one of the STM32 pins,

No. It just brings the benefit of being able to disconnect VBUS e.g. to a faulty device.

> or could I use 5V instead?

Yes. In a real-world application, you should limit the current, though, as a protection.

> Do I need to connect VBUS to the STM32 in order to detect that a device is connected?

No.

JW

View solution in original post

waclawek.jan · ‎2020-01-20

> Is it crucial that VBUS is connected (via current limiter power switch) to one of the STM32 pins,

No. It just brings the benefit of being able to disconnect VBUS e.g. to a faulty device.

> or could I use 5V instead?

Yes. In a real-world application, you should limit the current, though, as a protection.

> Do I need to connect VBUS to the STM32 in order to detect that a device is connected?

No.

JW

Lars Beiderbecke · ‎2020-01-20

Excellent! Thanks, Jan, for your quick response.