Question: It is unclear in the C2xx documentation (both User Guide and data sheets) whether PLL5V is a logic signal to enable the PLL or power supply input to the PLL circuit. I was advised that PLL5V is a power signal; therefore, it should be tied directly to 5V and not be connected through a pull-up resistor. However, I found that Spectrum Digital has it pulled-up through a 10K ohm resistor. Also if it is a power input then what about for 3V devices. The User Guide says to connect PLL5V to ground.

Answer: PLL5V is a logic input that tells the PLL whether it will be operating from a 5V or 3V power supply. If PLL5V=1 then the PLL will internally adjust for a 5V power supply; if PLL5V=0 then the PLL will internally adjust for a 3.3V power supply.