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LMX2572: direct VCO output problem

Tobias Pfeifer
Prodigy 30 points
Part Number: LMX2572
Other Parts Discussed in Thread: LMX2594, LMX2595

I have problems with output power at RFOutAP. RFOutAM is symmetrically terminated into a 50 Ohm resistor and OutB powered down.

My goal was to implement a step by step ramp in full assist mode, since I couldn't get the manual ramp to lock quick enough. This ought to go from 4 GHz to 6 GHz, so OUTA_MUX = 1 (direct VCO output).

When I sweep through from 1.6 GHz to 6.4 GHz I get decent power from the channel divider output, but when the MUX out is switched to VCO the output power almost vanishes.

Similar ramps work on LMX2594 and also LMX2595.

I removed pull up reistors at output of the 2572 and almost tried every setting for OUTA_PWR.

Do you have any idea?

  • 0
    TI__Guru* 92420 points
    Hi Tobias,

    Were you able to get normal output power in no assist mode?

    I don't understand the following statement. if the output is 6.4GHz, then the MUX must be VCO.
    *****When I sweep through from 1.6 GHz to 6.4 GHz I get decent power from the channel divider output, but when the MUX out is switched to VCO the output power almost vanishes.*****