Datasheet

User’s Guide
March 2012
March 2012 SNLU098 LMK00101 Users Guide 5
An XTAL with the HC49 footprint can be populated on the bottom side of the PCB. Alternatively, a
3.2 x 2.5 mm XTAL can be populated on Y2, located on the top side. Only one XTAL footprint
should be used at a time.
The values of C42 and C25 (C
EXT
) depend on the load capacitance (C
L
) specified for the crystal. The
OSC input capacitance (C
IN
) of the device is 1 pF differential, and the trace capacitance (C
TRACE
) of
OSCin and OSCout is around 1 pF. If the selected crystal is specified for C
L
of 18 pF, the C
EXT
is
calculated as follows:
C
EXT
= (C
L
– C
IN
– C
TRACE
/2) * 2
C
EXT
= (18 pF – 1 pF – 1 pF/2) * 2
C
EXT
= 33 pF
5.2 Configuring OSCin for a Crystal Mode
To configure the board to use crystal mode remove C26 to disconnect the OSCin Port. Install 0 Ohm
resistors on R33 and R34. Install a crystal in either footprint (Y1 or Y2) and install the proper load
capacitors in C24 and C25.
6. Clock Outputs
All clock outputs are LVCMOS. In the case that not all outputs are used, any unused outputs should
be left floating.