USB power vs Vin power

[bdoan]

The product page for the Teensy 4.1 states:


When USB power is not used, 5V power may be applied to the VIN pin. Because VIN & VUSB are connected, power should not be applied to VIN while a USB cable is used, to prevent the possibility of power flowing back into your computer. Alternately, a pair of pads on the bottom side may be cut apart, to separate VUSB from VIN, allowing power to be safely applied while USB is in use. (TODO: VUSB-VIN pads photo, right side)

Does the processor attempt to detect voltage from the Vusb before attempting to enumerate or if it is powered from the Vin pin, does it just respond to the code in the setup() ?

 

[jmarsh]

It enumerates whenever the host asks it to regardless of how it is powered.

 

[bdoan]

It enumerates whenever the host asks it to regardless of how it is powered.

So are you saying that the Vbus pin from the host USB connector is not sensed when the Teensy is powered from the 5V pin?

 

[jmarsh]

If you've cut the connection between VBUS-VIN, VBUS isn't connected to anything. It's just a floating pad.

 

[defragster]

As long as USB GND is common and the Teensy is active (VUSB, or trace cut and 5V powered) the USB D+ & D- when active from host will connect as normal.

 

[bdoan]

If you've cut the connection between VBUS-VIN, VBUS isn't connected to anything. It's just a floating pad.

Thanks

 

[BriComp]

You could look at the Circuit Diagram here, it shows the pads to be cut as in the pic below. I have circled the pads in RED.

 

[bdoan]

Yes, I see that.
My confusion was that all other processors that I have used sense the Vbus to begin enumeration