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Original question:

LMX2820: Current consumption in TiCSPro

LMX2820: Current consumption higher than datasheet indicates when in EXT VCO mode (Evaluation Board)

Leonard Cordingley
Prodigy 55 points
Part Number: LMX2820

When operating the LMX2820 using its Evaluation Board and controlling it using the GUI, I find that the current consumption is higher than indicated in the datasheet.

I am using it in External VCO mode, and the TICS-PRO GUI is set up to do that, but I checked the current and the clamp on meter reads 414mA. The datasheet says it should draw 290mA in External VCO Mode. Are there settings in the LMX2820 which the GUI is not entirely disabling when the user selects EXT VCO? Is the user supposed to disconnect the VCC_VCO or VCC_BUF lines from the 3.3VDC supply to ensure that the consumption meets the published data? 

  • 0
    TI__Guru** 108200 points

    Hi Leonard,

    Default configuration of the GUI uses internal VCO and has RFOUTA enabled. 

    When it is switched to external VCO mode, RFOUTA is still enabled, but in reality, there is no signal coming out from RFOUTA. So we should disable it (OUTA_PD=1) to save power. 

    In addition, datasheet test condition is fosc = fpd = 100MHz. Now the GUI estimates current consumption is 253mA.

  • 0
    TI__Mastermind 28011 points

    Just measured 274 mA.  Now I didn't have an external VCO hooked up, but seems far off from your 414 mA.

    A few things:

    1. OSC2X=0

    2. If you have an actual VCO hooked up, don't forget to subtract out that current.  Also, it probably needs the phase detector polarity changed from negative to positive.

    3. I think that this number is with both output buffers off, that's what I did.