USB power connection options

[MaxM]

Our design doesn't have 5VDC on the MCU board, USB 5V for the USB drive is generated further downstream. What are the options to make USB work?:

1) Connect MCU VDD 3.3V to VDD_USB_CAP through a Schottky. USB_OTG1_VBUS unconnected.

2) Connect MCU VDD 3.3V to USB_OTG1_VBUS

 

[MaxM]

Thank you, Jing.

>USB_OTG1_VBUS must be 5V input, please connect it to USB 5V.
The MCU board doesn't have USB_5V rail or any other 5V rails available.

I tried both approaches on the EVK and they both work. I'm inclining towards (2) - powering VDD_USB_CAP from VCC_3V3, as (1) clearly violates the operational requirements. Is there any risks associated with this solution?

[jingpan]

Hi @MaxM ,

If you needn't USB, just keep USB_OTG1_VBUS floating.

If the USB is used, you'd better don't connect the pins in this way. I don't know if there is any risks associated with this solution. The IP just isn't designed in this way.

Regards,

Jing

[jingpan]

Hi @MaxM ,

USB_OTG1_VBUS must be 5V input, please connect it to USB 5V.

VDD_USB_CAP can connect to a cap, but don't connect to other power.

If USB function is not needn't, just float USB_OTG1_VBUS.

Regards,

Jing