SI5040-EVB Datasheet, PDF (6/24 Pages) Silicon Laboratories – Four selectable on-chip reference frequencies

Si5040-EVB
attenuates the RD signal, which requires that the RD
signal level from the Si5040 be slightly increased.
Please use the Si5040 Register 56 to increase the RD
drive signal from its default value of 600 mV to either
700 or 800 mV. See the Si5040 datasheet for more
information. The circuit that is implemented on the EVB
is shown below:
5040
RD+
20.5
XFI RD+
274 
3.0 pF
.01 uF
5040
RD-
20.5
3.0 pF
XFI RD-
274 
.01 µF
Figure 8. EVB Pre-Emphasis Circuit
Within an XFP module, the pre-emphasis circuit should
be located as close to the Si5040 RD± pins as is
practical. In an XFP module, the pre-emphasis circuit
above can be modified to remove one component yet
still behave the same electrically. The following circuit
shows this simplification.
1.7. Start Up Script(s)
1.7.1. For Evaluation Boards Populated with the
Rev. A Device
It is necessary to load the scripts included with the
evaluation board software at startup and after any reset
of the Si5040 Rev A. The default name for the initialization
script is "Si5040InitialRegisterMapSettings.txt". This
script will set up the Rev A device in Mode 0, the
Reference-less operation mode.
If you need to set up the Rev A device in Mode 3, the
jitter attenuation mode with external crystal
"Mode3OvtInit.txt" script needs to be loaded after
"Si5040InitialRegisterMapSettings.txt" is first loaded.
Note that these scripts should be loaded by using the
Register Programmer. See "2.5. Si5040 EVB Software
Description" on page 8 for more information on the
Register Programmer.
1.7.2. For Evaluation Boards Populated with the
Rev. B Device
Starting Oct 2006, no initialization script is required for
Mode 0 operation. However, in order for the interrupt pin
to function properly on the evaluation board, Register 2
needs to be set to 18h (default=58h) by using the
Register Programmer. Note that this is to set the
interrupt output driver as CMOS as the evaluation board
does not have an external pullup on the interrupt signal.
If you need to set up the Rev B device in Mode 3,
Register 134 needs to be set to 3h (default=30h) by
using the Register Programmer, or simply go to System
Programmer and click on the TX CDR/CMU Control link
in the block diagram. Then, choose "Mode 3" from the
"cmuMode" pull-down menu.
5040 RD+
20.5
274 
XFI RD+
3.0 pf
3.0 pf
.01 µF
5040 RD-
20.5
274 
XFI RD-
Figure 9. Recommended XFP Pre-Emphasis Circuit
Should you not like the eye pattern at the RD± pins, this
circuit can be easily optimized for your application. If
you wish assistance in this matter, please contact Siicon
Laboratories.
6
Rev. 0.4