6. External Reference Input (XA/XB)
An external reference (XTAL) is used in combination with the internal oscillator to produce an ultra-low-jitter reference clock for the
DSPLL and to provide a stable reference for the free-run and holdover modes. The Si5395 EVB can also accommodate an external
reference clock instead of a crystal. To evaluate the device with a REFCLK, C111 and C113 must be populated and the XTAL removed
(see the figure below). Also, R197 and R202 must be populated. The REFCLK can then be supplied to J39 and J40. In the case of the
Si5395J-A, which is the grade with the xtal internal to the device, there will be no external xtal supplied on the board and no input from
Ref_XA and Ref_XB. In this case, it is advised to remove R197 and R202.
Figure 6.1. External Reference Input Circuit
UG335: Si5395 Evaluation Board User's Guide
External Reference Input (XA/XB)
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