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Original question:

LMX2595EVM: LMX2595EVM

LMX2595EVM: Output path configuration

Liu Yang
Expert 8775 points
Part Number: LMX2595EVM

Hi Team,

The output path is configure as differential and understand if using single ended, we need to add a pull up resistor/inductor. I try out with the EVM board, if the unused port (-ve) terminated with 50ohm terminator the output power at (+ve) drop by 1 dB. So, what is the recommendation from TI or can i just leave the port open? What is the impact if the other port just left it open (only pull up resistor). Measurement done with SA shown no different in term of Spur and Phase Noise.

Beat Regards,
Tom Liu

  • 0
    TI__Guru** 107740 points

    Hi Liu Yang,

    In the same buffer (e.g. RFoutA), both pins need to be pulled up in the same way. If you pull up the +ve pin with an inductor, the -ve pin, even if you are not using it, should also be pull up with an inductor of the same value. 

    If a buffer is not used, no pull up is required, just leave the pins open. 

  • 0 in reply to Noel Fung
    TI__Expert 8775 points

    Hi Noel,

    I do understand that if we pull up the output pin (either resistor or inductor), we need to do it in both (+ve) & (-ve). My question is, if we only used +ve as configure as single ended, does the other side -ve pin need to be terminated with 50ohm? I have try out if terminate with 50ohm, the output power at +ve pin is drop by 1dB.

    Beside you mention if buffer is not used, it this mean if we only need single channel output the other output can be left open without any pull up component?

    Beat Regards,
    Tom Liu

  • 0 in reply to Liu Yang
    TI__Guru** 107740 points

    Hi Tom,

    yes, if only +ve is used, -ve needs to be terminated as well. 

    -ve pin ----pull up ----DC block --- 50Ω shunt.

    If you use RFoutA only, RFoutB should be disabled (OUTB_PD = 1) and the pins can be left opened.