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10
SNAU076B
LMK04800 Family
Revised - August 2014
Copyright © 2014, Texas Instruments Incorporated
5. Visual Confirmation of Frequency Lock
After a default mode is restored and loaded, LED D5 should illuminate when PLL1 and PLL2 are locked
to the reference clock applied to CLKin1. This assumes LD_MUX = PLL1/2 DLD and LD_TYPE =
Active High, which are the default settings.
6. Enable Clock Outputs
While the LMK048xxB offers programmable clock output buffer formats, the evaluation board is shipped
with preconfigured output terminations to match the default buffer type for each output. Refer to the
CLKout port description in the Evaluation Board Inputs and Outputs section.
To measure phase noise at one of the clock outputs, for example, CLKout0:
1.
Click on the
Clock Outputs
tab,
2.
Uncheck “Powerdown” in the Digital Delay box to enable the channel,
3.
Set the following settings as needed:
a.
Digital Delay value
b.
Clock Divider value
c.
Analog Delay select and Analog Delay value (if not “Bypassed”)
d.
Clock Output type.
4.
Depending on the configured output type, the clock output SMAs can be interfaced to a test
instrument with a single-ended 50-ohm input as follows.
a.
For LVDS:
i.
A balun (like ADT2-1T) is recommended for differential-to-single-ended
conversion.
b.
For LVPECL:
i.
A balun can be used, or
ii.
One side of the LVPECL signal can be terminated with a 50-ohm load and the
other side can be run single-ended to the instrument.
c.
For LVCMOS:
i.
There are two single-ended outputs,
CLKoutX and CLKoutX*, and each
output
can be set to Normal, Inverted, or Off.
There
are nine (9) combinations of LVCMOS
modes
in the Clock Output list.
ii.
One side of the LVCMOS signal can be
terminated with a 50-ohm load and the
other
side can be run single-ended to the
instrument.
iii.
A balun may also be used. Ensure
CLKoutX and CLKoutX* states are
Figure 7: Setting LVCMOS modes
Figure 6: Setting Digital Delay, Clock Divider, Analog Delay, and Output Format for CLKout0