7©2018 Integrated Device Technology, Inc. February 12, 2018
VersaClock
®
6E - 5P49V60, 5P49V6965 and 5P49V6975 Evaluation Board User Guide
On-board Crystal
A 25MHz crystal is installed on the board with the 5P49V60 and 5P49V6965. If the evaluation board is assembled with a 5P49V6975, no
crystal is assembled because the crystal is integrated in the device. The crystal pins on the 5P49V6975 are NC (no connect).
Figure 6. Crystal Circuit
The board is shipped with a small 25MHz SMD crystal installed. The crystal can be replaced with a different frequency if needed. Note
that Output 1 with the default or “test” mode will only work when using a 25MHz crystal.
A thru-hole crystal can be assembled in the X1 position. Remove the small 25MHz crystal and also assemble the resistors R78 and R79
to connect the thru-hole crystal.
Another useful modification can be to remove the 25MHz crystal and assemble C6 to connect the SMA connector J6. Now a clock from a
generator or other source can be used to drive the XIN pin. Also assemble R17 when termination of the external clock is needed. Please
look up the requirements for the XIN amplitude in the device datasheet. Essentially, the amplitude on XIN should not exceed 1.2Vpp and
we recommend using 1.0Vpp for most tests. When doing phase noise measurements of the output clocks, use a very low noise clock for
XIN. The best phase noise at the outputs is achieved when using a crystal. Only the very best of low noise RF signal generators
connected to XIN can result in the same phase noise performance.
