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LMX2694-SEP: Output Buffer Current Draw

Chris Zuhlke
Prodigy 50 points
Part Number: LMX2694-SEP

We will be using pull-up resistors on the output lines, and I want to be certain we don't over power the resistors.  What is the output buffer current draw versus output power setting?  I did not find this information in the datasheet.

Thank you!

  • 0
    TI__Guru** 107030 points

    Hi Chris,

    The total current drawn for VccBUF and the pull-up resistors varies from 138mA (one direct VCO output) to 178mA (one divided down output) to 296mA (one direct VCO output, one divided down output). Power setting (OUTx_PWR) is 31. 

  • 0 in reply to Noel Fung
    Prodigy 50 points

    Hi Noel,

    Thank you for the quick answer to my inquiry!  That sounds like a lot of current flowing through the pull-up resistors.  There may have been a misunderstanding to my question, and I should have worded the question differently.  I am looking for the current draw of the RFOUTA pins, which would also be the current flowing through the pull-up resistors.  The current levels you mentioned seem extremely high to flow through the 50 ohm pull-ups.

    Thanks again,

    Chris

  • 0 in reply to Chris Zuhlke
    TI__Guru** 107030 points

    Hi Chris,

    The current I mentioned consists of the current flowing through the resistors as well as the output buffer.

    The current flowing through the resistors depend on the output power setting (that changes the output voltage swing). Lets say VOH is 2V at RFoutAP, then the current flowing through the resistor is (3.3V - 2V) / 50 = 26mA. If VOL is 1V, then the current is 42mA. So the total current flowing through the resistors in RFoutA is 68mA. 

    Output power setting will change VOH and VOL.