FS6131

Note: As an update to this data sheet, the FS6131 hardware is no longer available from ON SEMICONDUCTOR.

10.2.3. Example: Line-Locked Mode

Selecting the line-locked/genlock option in the Device Mode block changes the program default settings. The Reference Source

changes to the REF pin input, and a block appears to permit entry of the REF input frequency in MHz. A Desired Multiple block allows

entry of the reference frequency multiplying factor used to generate the output frequency.

Exercise: Change the ref pin frequency to 0.0315MHz, and alter the desired multiple to 800. Change the loop filter block to external,

but leave the values for C1 and R alone.

Click on Calculate Solutions. The program takes into account all of the current screen settings and calculates all possible

combinations of reference, feedback and post divider values that will generate an output frequency from the input frequency (31.5kHz)

multiplied by the desired multiple of 800.

A box will appear: "No solutions were found! Do you want to retry calculations with the check loop stability option turned off?" Choose

Yes.

Another box may momentarily appear: "Calculating Solutions: Press cancel to stop with the solutions calculated so far." A number in the

box will increment for every unique solution that is found. This example will create eight unique solutions, which are then displayed in a

window in the lower right portion of the program screen.

For best results, try to keep the PostDiv value multiplied by the FbkDiv value from getting larger than 5000 while running the VCO as

much above 70MHz as possible. If a tradeoff must be made, it is better to run the VCO faster and allow the divider values to get large.

Solution #3 provides a PostDiv value of 4 and a FbkDiv value of 800 for a combined value of 3200. The VCO is running at about

100MHz.

Click on Solution #3 to highlight the row, then click on Suggest in the Loop Filter box to have the program choose loop filter values.

Suggested values for an external loop filter are 4700pF and 47kW.

Now reselect the Check Loop Stability box to turn this feature on. Clicking on Calculate Solutions regenerates the same solutions

provided earlier, only this time the new loop filter values were used.

Figure 20: Line-Locked Screen

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