We're trying to use the LMX2582 to generate frequencies in the 47-75 MHz range, and we're seeing problems with the channel divider.
If we configure the eval board with the /196 channel divider setting, we see good outputs up to the maximum VCO frequency. With the /128, /96/, and /64 channel dividers configured per the datasheet, we see the output get unreliable above a VCO frequency of ~6.6 GHz. In the /96 mode, we can fix the issue by changing the dividers - the recommended /2->/8->/6 patter has issues, but /3->/8->/4 works. Running this through TICS Pro and PLLatinum Sim, neither one indicates that this should be a problem.
It looks like the problem is related to the CHDIV SEG1 being set to /2 - but only when also used with additional dividers (if we just use SEG1 alone, it seems to work).
Table 4 of the datasheet gives guidelines for setting the channel divider, but it's not clear - if I want to generate 52 MHz, should I be using /96 or /64? In our application, we need to generate a wide number of arbitrary frequencies, so we need to be able to calculate the correct settings on the fly, and know that it will be reliable across temperature and process variation. Would it be possible for TI to provide something similar to Table 4, but showing the allowable output frequency range usable with each divider setting?
Thanks -
