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LMX2594: The settings for Register 25 in TICS do not match the datasheet

Josh Merti
Prodigy 190 points
Part Number: LMX2594
Other Parts Discussed in Thread: LMX2595

I'm trying to get the LMX2594 operating on my board and one thing I noticed was the register settings for Register 25 that are read from the LMX2594 eval board are different than the settings in the datasheet.  The datasheet says to set Register 25 to 0x0624 but the eval module reads back 0x0C2B.  There is no description of this register and no controllable fields in Register 25.  Which settings are correct?

  • 0
    TI__Mastermind 27981 points

    Josh,

    This setting will not impact LMX2594 performance, but here's more details ...

    When the part powers up, it sets all registers to a power on reset value.  However, it is NOT always the case that the power on reset value is the recommended value.  This is why we have registers in TICSPro and the datasheet that show 1's and 0's.  These are the recommended values, which is what you should program them to.

    Now R25 is a special register to discuss.  This actually controls the settings for the output doubler.  As the LMX2594 has no output doubler, it really has no impact, so either setting is fine.  However, for the sister part, the LMX2595, we have found that changing this setting from 0x190624 to 0x0190C2B improves both the performance and output power.

    So the plan is to update the datasheet to make R25 = 0x0190C2B.  It doesn't impact LMX2594, but just doing it to be consistent.  We will put a note to say that you also can set R25 = 0x190624 for the LMX2594 with no performance impact.

    Regards,
    Dean