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Clarify requirments of USB Vregin.  Does USB really work with Vregin down to 2.7V?

Question asked by David Burton on Mar 14, 2016
Latest reply on Mar 16, 2016 by David Burton

There are quite a few posts on Vregin and Vout33 and USB, but none that I have found completely clarify the issues.

The K20P48M50SF0 data sheet says Vregin can be 2.7 to 5.5V

Vout33 supplies the internal USB transceivers.

Vout33 regulator is internally powered from Vregin.

Vout33 can be connected to an external 3.3V supply, which I assume would then be the power for the transceivers and the internal Vout33 regulator would do nothing.

 

The Vout33 internal regulator is specified to be 3-3.6V or 2.1-3.6V(standby) output.

 

It's stated in other posts that Vregin must be connected for USB to work, even if Vout33 is connected to an external regulator. 

Is this true if I am providing 3.3V to Vout33 from an external regulator?

If I provide 3.3V to Vout33, then will USB still work if Vregin is also connected to 3.3V?  Does it need to be higher than 3.3V?  If so, why is that, if my external 3.3V is powering the USB transceivers?

 

I have 3.3V on board, but my host controller does not want to provide me 5V over the USB cable. (dedicated application).

 

Thanks.

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