USB on an 18F25K50 at 3.3V

[JAM2014]

Hi All,

For a number of reasons I'm updating an older 18F2550 project design with USB that runs at +5V to a +3.3V design. Because I want to be able to run
up to 48MHz, I've selected the 18F25K50 for the new design. I was under the impression that this PIC would run at 3.3V, and do USB as long as I
disabled the internal Vusb regulator, and connected the Vusb pin to Vdd. But, I don't find a Fuse in the 18F25K50.h file that looks like it controls the
internal regulator, so at this point I'm stuck.

Is my thinking correct that this device should do USB at 3.3V, and is this the correct way to do it?

Thanks,

Jack

[temtronic]

Downloaded the datasheet and that PIC is good at 3v3 to run USB fine at 48MHz.

If you look a t figure 24.1 you'll see...you need to disable the internal pullups.
UPUEN=0

You'' have to scan the 'header' to see what CCS calls it and add external pullups to Vdd.

cheers
Jay

[Ttelmah]

There isn't any control for the internal regulator. Look at the USB diagram in the data sheet. Basically the regulator is there for the F devices and not there for the LF devices. No control bit for it.
Quote from the data sheet:
"F devices permanently enable the voltage regulator". (Section 2.4).
You need the LF device.
You can still use the internal pull-ups.

Problem is that the data sheet is for both chips, so you have to work out what parts apply to which chip....

Problem also is that the 'voltage range' diagrams for the chips ignore the USB component. On the F devices, Vdd, must be at least 0.3v above Vusb.

The LF device at 3.3v is great.