K60 - using VREGIN pin in USB device mode

[panpwr]

Hello,

I couldn't find an explanation regarding the logical role of this pin. I understand that - electrically - it takes an input of 5V from the USB device, and outputs 3.3V through VOUT33 pin - in order to use it for powering the Kinetis circuit.

However, I already power the circuit from an external 3.3V source, so I don't need this functionality. Nevertheless, the device won't work in USB device mode (no events are triggered to SW) if this pin is not being supplied from the USB device with 5V.

Is there a way to disable the usage of this pin using SW, or I would have to connect it to the USB device's VCC line?

Thanks,

Lior.

[Kari]

Hi Lior,

VREGIN is the input for the internal USB regulator. The USB block of the kinetis powers itself from the internal regulator only.

Look at

3.9.2 Universal Serial Bus (USB) Subsystem

from the reference manual.

Regards,

Kari

[jonpry]

Is there a way this behavior could be used to detect VBUS presence for a device only setup? I don't have any gpio pins available. 

[panpwr]

Hey Kari,

Thanks for picking this up. There is still something I don't understand:

We've operated the USB in host mode without attaching anything to this pin. How come the regulator doesn't needs to be fed in this mode, if this is the USB block's only source of power?

[florintoma · Accepted solution]

As Kari said, USB KHCI controller is bus powered only. If you check the RM at sub-chapter 3.9.2.2.1 fig. 3-54 the USB controller is powered only from USB Regulator which is powered from VBUS. The USB in host mode without VREGIN to VBUS, only provides VBUS power for the device conected but the USB controller will not work. I've tested myself on 2 different K60 revisions.