The spec says 50 ma max for the 3.3 volt output on the Diecimila... I want to runt the XBee from the 3.3 volt output. The spec on the XBee says 50 ma. Well - I know that is within the spec, but is it a bad idea to run things this close to the limit? Should I just provide my own 3.3 volt power to the XBee?
Brandon
The 3.3V output on the Diecimila is provided by the FT232 (USB interface)'s internal regulator and primarily designed for running the USB transceiver, as a courtesy they provide the 3.3V output for other low-current tasks. If you draw more than 50mA, the output voltage will drop, eventually browning out the USB transceiver. (If you're not using the USB transceiver, it is possible to draw more current from the 3.3V output, but it's undefined.)
Without knowing the wording of the XBee unit's datasheet, it's hard to give a definitive answer, but your always safer using a separate regulator.
You're better off adding a separate 3.3V supply, it's disturbingly easy to overload the ftdi 3.3 V output.