Can you better explain your power supply system ?
Is it :
a/ self powered
b/ powered BOTH by USB (while connected) and self powered ?
Regarding power consumption, I think it does not have any influence whether you use PLL or not (assuming of course similar Fcy) as far as the datasheet electrical data are concerned BUT you should consider the following tips :
a/ the fastest restart from sleep mode is done using internal RC oscillator
b/ the slowest start/restart is the PLL configuration because you must consider the PLL lock time
c/ the best solution (when possible) is to actually restart from internal RC and then switch over to the main XTAL oscillator (if necessary) by checking the bit which tells you that the main oscillator is stable. Doing this you can optimize your power budget
Another tip is to run the main clock as low as possible (depends upon your application). The USB and the CPU clock can be programmed separately using the prescalers which gives a lot of possibilities on this micro.
Can you also explain which Fosc / Fcy you're using ?
I see no possibility other than using an I/O to detect connection/disconnection if you are self powered...
post edited by RISC - 2009/04/25 02:29:03