What to do with unused USB VREG VOUT33 pin?

[nickdolling]

Looking for guidance on what to do with the USB voltage regulator pins when the USB module is not being used in the design. The datasheet says to leave USB_DP and USB_DM unconnected, and I guess it's normal for the VREGIN to be unconnected, but what about VOUT33?

It must be internally connected.. does it need the capacitor still?

[bobpaddock]

The minimum VREGIN specified in the datasheet is 2.7V.

Having an unpowered section can present odd load impedances to the powered sections of a chip, so I would connect VREGIN to something.

If the regulator is in turn, turned off, there is no need for caps on VOUT33.

[nickdolling]

Thanks for  your reply.. normally I would agree, but in this case the USB regulator is specifically designed to be unpowered when the USB is not in use.

The RM section on it is pretty vague.. it mentions a shutdown mode but says nothing about how/when it's used. There are no registers associated with it so it would seem that it's completely analog/automatic.

The RM section on USB shows various power supply configurations with some sketchy drawings which suggest there is no internal connection of the VOUT33 to anything other than the USB transceiver, but I'd rather have something more definitive.

My main concern is as you suggest.. if there is anything other than the regulator internally connected to VOUT33 that would rely on the capacitance there.

Nick