Would this USB detection circuit work as expected?

Using Arduino General Electronics
1

What I am trying to achieve is detect from MCU, whenever FTDI(FT232R) chip is connected to USB(not enumerated, just powered up from USB).

  • When ONLY USB is connected, MCU will get his power supply from +5V bus and will detect on (B) pin that USB is connected.

  • When ONLY VR will supply power to circuit, then MCU again will get power from +5V bus, but FTDI will ONLY get VCCIO. On middle of voltage divider R10/R11 I expect there will be 0 and MCU will not detect USB connection on (B).

The question is - would it work the way I described or I missed something? My concern is it ok to hook up only VCCIO to FTDI? Would it damage or lead to unknown behavior?

2

I think the use of reset from the divider might create problems. Usually you need a stable supply and then apply reset, but if you conenct both the supply and reset to the same thing, you really are guessing the outcome, especially with mechanical connections like usb. I would use 2 rc filters, one with a longer constant for reset, but even that is a bad idea.

I don't know what would happen if you power one vcc and not the other, it is a good question.