I´m working on a new design with MPC5744 (LQFP) microcontroller. As far as I know, the crystal unit drive level could be obtained from the following equation:
Taking in to account MPC5744 evaluation board, we have following values:
Rlà crystal series resistance 50R
VDDà1,7V (from datasheet)
Clà8 pF (stray capacitance 4 pF)
Coà6 pF (shunt capacitance)
Applying those values in the equation I obtain that the crystal unit requires 894uW Drive level. I don’t understand how the eval board crystal unit could work, as it has a 500uW drive capability.
I think that I´m doing something wrong but I don´t know what.
Thanks in advance.