Si5345-44-42-D-RM
62
Rev. 1.0
Figure 36. Clipped Sine Wave TCXO Output
Figure 37. CMOS TCXO Output
The Si5345/44/42 can also accommodate an external reference clock (REFCLK) instead of a crystal. Selection
between the external XTAL or REFCLK is controlled by XAXB_EXTCLK_EN, the LSB of register 0x090E. The
internal crystal loading capacitors (CL) are disabled when an external clock source is selected. A PXAXB prescale
divider is available to accommodate external clock frequencies higher than 125 MHz as shown in Table 38. For
best jitter performance, keep the REFCLK frequency above 40 MHz.
For applications with loop BW values less than 10 Hz that require low wander output clocks, using a TCXO as the
XAXB reference source should be considered to avoid the wander of a crystal.
V3P3
Si5345/44/42
VDD
OUT
TCXO
GND
XA
XB
100 nF
100 nF
Si5345/44/42
XA
XB
100 nF
V3P3
VDD
OUT
TCXO
GND
453
100 nF
453
100 nF