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LMX2592: 50 ohm termination on RF outputs on EVM

Izik
Expert 1555 points
Part Number: LMX2592

Hello 

Looking on the LMX2592 EVM schematic, I've noticed that there are 50 ohm resistors to ground at RFOUTAP and RFOUTAN outputs. These terminations are not connected on the EVB. Can you please confirm that they are not needed when connecting 50 ohm load (such as spectrum analyzer for example) to RF outputs?

Thanks 

  • 0
    TI__Expert 7965 points

    Izik,

    I think you mean 50 ohms to Vcc. These outputs are open collector, which needs the pull-up to Vcc. The two outputs are the exact same, just in the EVM we have RFoutA have standard 50 ohms, whereas RFoutB uses inductor pull-up which lets you experiment with the effect of an inductor giving higher impedance at resonant frequency and thus a different output power profile. The datasheet applications section discusses more on how to select this inductor value.

  • 0 in reply to Brian Wang
    Expert 1555 points
    Hello Brian

    I mean to resistors R34 and R32 in the EVM schematic

    Thanks
  • 0 in reply to Izik
    TI__Guru* 88320 points
    Hi Izik,

    These resistors are not needed if they are connected to other 50ohm load such as SpecAn. However, if only one of the pins is 50ohm loaded, the unused pin should also be 50ohm terminated.