5. External Reference Input (XA/XB)
An external reference (XTAL) is required for Grade A in combination with the internal oscillator to produce an ultra-low jitter reference
clock for the DSPLL and for providing a stable reference for the free-run and holdover modes. The Si5372-EVB for these versions can
also accommodate an external reference clock instead of a crystal. To evaluate the device with a REFCLK, C93 and C94 must be
populated and the XTAL removed (see the figure below). The REFCLK can then be applied to J25 and J26.
In the case of the
Si5372J-A which is the grade with the internal XTAL, 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 any resistor connections to XTAL1 and XTAL2 on component Y1.
Figure 5.1. External Reference Input Circuit
UG372: Si5372 Evaluation Board User’s Guide
External Reference Input (XA/XB)
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