Clock Circuitry
MPC5746R Hardware Design Guide, Rev. 1
NXP Semiconductors 21
Figure 9. Internal Crystal Load Capacitors and Crystal Connections
Since the layout of the module/board can affect the component values required, customers should have
their board characterized by their crystal vendor to recommend values for C
X
and C
Y
. The values shown
in this document should be used as a starting point. These should be re-characterized for any change to the
oscillator circuit layout, including routing changes of other circuitry near the crystal circuit.
The crystal should be placed as close as possible to the MCU. In order to minimize signal degradation, the
circuitry should be placed entirely on only one PCB layer, avoiding unnecessary vias where ever possible.
Do not allow any signals to cross the crystal connections to the device. Absolutely no high current or high
speed signals should be run near any of the crystal components.
Other than the connections shown in the figure above, no other connections should be made to the crystal
or EXTAL and XTAL device pins. Do not use XTAL to drive any other circuitry.
The following figure illustrates an example circuitry of oscillator with ground routing with external load
capacitors.
Figure 10. External oscillator circuitry example
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