USB power on a PIC

Thread Starter

KansaiRobot

Joined Jan 15, 2010
324
Hello everybody and thanks always for your help.

I have a question regarding USB powering for a PIC. I am using the 18F2550 and the 18F2553 that have USB capabilities. Now, in the past -using a development board that had incorporated a crystal oscillator of 20MHz I had communicated the PIC and the PC.

Right now, I am not using that board but just a simple IC. Now, I am using the internal oscillator for A/D etc, so no problem there but I ve read in the datasheet that you need a crystal for the USB data communication to work, because the USB functions are timed by that.

But how about if I just want to only power my IC from the USB? I have the schematics of where to put the Vusb and the GND pins but do I still need a crystal for this too??? (notice I am not going to pass data in or out)

Thanks for the help
 

tracecom

Joined Apr 16, 2010
3,944
But how about if I just want to only power my IC from the USB? I have the schematics of where to put the Vusb and the GND pins but do I still need a crystal for this too??? (notice I am not going to pass data in or out)
No. However, if the USB is from a PC, you will not be able to enumerate the USB, and so will be limited to 100mA.
 
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