Equivalent Circuit of XTAL of MPC5643L

[zhangcindy]

Could you please provide value of the resistor of equivalent circuit between XTALIN and XTALOUT, in of MPC5643L datasheet Rev 9, Page 91?

[zhangcindy]

The current through crystal is decided by the resistor in the device. If resistor is higher, current is lower, and the crystal power dissipation is smaller. So, it need to know the value of resistor to calculate the max power of the resonator. If the power dissipation of crystal is more than rated power , we should improve the outside circuit. Please kindly help to provide this info.

[davidtosenovjan]

Value of internal bias resistor R is not available. However external bias resistor value is recommended as 0 Ohms. I believe you don’t need to know the value.

The recommended configuration for maximizing the oscillator margin are:
XOSC_MARGIN = 0 for 4 MHz quartz
XOSC_MARGIN = 1 for 8/16/40 MHz quartz

The ALC (automatic level control) increases the bias current to amplify XTAL signal in order to maintain that constant signal level on EXTAL.