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AFE11612-SEP: Output Cap drive with series resistance

Steve Widener
Genius 9865 points
Part Number: AFE11612-SEP

Hi - the datasheet specifies a maximum output capacitance for the DACs of 10nF.

If we provide a series output resistor from the output of the DAC, are we able to increase the capacitance?

We are planning to put a 1Kohm / 1Kohm divider on the output of the DAC channels with a 0.1uF or even 1uF cap at the divider node to GND. 

Please advise, would this cause any issues with the DAC outputs? How low could the output resistor be before we'd see issues @ Cout > 10nF?

  • 0
    TI__Expert 5730 points

    Hi Steve,

    From some tests I've performed in the past, 1uF should be fine for the DAC output. There's a range of capacitance that would cause the output to oscillate, though I don't know this offhand. Give me a day or two to run some tests to see how the output changes with different capacitances and resistances.

    Thanks,
    Erin

  • +1 in reply to Erin Guthrie
    TI__Expert 5730 points

    Hi Steve,

    I've run some rough tests on my own setup with different capacitances and resistances. The primary issue with going over 10nF is it could cause the DAC output to ring. Adding a resistor helps with the ringing, but you trade that for output time. Here are my results:

    0.1uF will cause oscillations on the output. A 100 Ohm resistor in series smooths this out significantly, making it a feasible combination.

     

    1uF causes the output to be critically damped. It does not significantly oscillate, but it takes longer to load. Next two plots are with 10 Ohms and 100 Ohms. 

    Thanks,

    Erin

  • 0 in reply to Erin Guthrie
    TI__Genius 9865 points

    Excellent - thank you!