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XTR300 25kHz Noise/Oscillation

David Fiori, Jr.
Prodigy 150 points
Other Parts Discussed in Thread: XTR300

The XTR300 is producing a 3mv P-P 25kHz oscillation/ noise. Is it an artifact of the internal chopping amplifier.

Is it getting into the system through the power supply lines coupling back to the input? Does anyone know if this can be eliminated without installing a filter on the output?

  • 0
    TI__Guru 62055 points

    Hi David, 

    Could you send let us know the input / output ranges of your system?  Also provide a schematic and a few scope captures of the following signals:

    1.) XTR300 output
    2.) V+
    3.) V-
    4.) GND

    Please ac couple the scope inputs and zoom in so we can observe the ripple on these four nodes. 

    It's probable that you're seeing the switching noise of the XTR300, but we'd like to take a look at the other nodes in your circuit to rule out issues from the power-supply.  The internal oscillator in the XTR300 operates at 100kHz and 25kHz is a submultiple of that frequency.  The XTR300 switching noise is below the threshold of most applications once the standard protection and filtering circuitry is added to the design.  This is covered on page  23 of the XTR300 datasheet in the "Internal current sources, switching noise, and settling time" section.  Take a look at the reference design:  TIPD155 for an example of an IEC61000-4 compliant output protection circuit with the XTR300. 


  • 0 in reply to Collin Wells
    Prodigy 150 points
    Thank you for your quick reply.

    Input/Output ranges are 0v - 3.3v input and -10v to +10v.

    For your information the noise is a triangle looking wave about 25kHz, 3mv P-P on the XTR300 output from the DRV pin. There is nothing on the V+, V- or GND.

    Currently using bench power supplies for +24, -15 volt supplies. I currently have the microprocessor halted, and I placed a large 2.2uF capacitor on the input to the XTR300 after the 750 ohm R32//R33 resistor to reduce anything from the DAC that might be causing this.

    As a few scope captures go I will have to take pictures of the oscilloscope with my iPhone and get them to you.

    How can I upload a schematic PDF and the screenshots?
  • 0 in reply to Collin Wells
    Prodigy 150 points

    Thank you for your quick reply.

    Input/Output ranges are 0v - 3.3v input and -10v to +10v. 

    For your information the noise is a triangle looking wave about 25kHz, 3mv P-P on the XTR300 output from the DRV pin. There is nothing on the V+, V- or GND.

    That part of the schematic of the product using the XTR300 in a .pdf format file: 

    XTR Schematic Screen Capture.pdf

    Following is a picture of the noise at 2mv per vertical division and 50usecs per division horizontally:



    Currently using bench power supplies for +24, -15 volt supplies. I currently have the microprocessor halted, and I placed a large 2.2uF capacitor on the input to the XTR300 after the 750 ohm R32//R33 resistor to reduce anything from the DAC that might be causing this. 

    Please feel free to call to discuss. My phone no. is 215-584-2214 (cell), my email is dfiorijr@anamir.com.