AD420 Unstable output voltage signal

Hello! I have a problem with ad420 voltage output. I need VOUT=0-10V. 

In my scheme i have 4 independent AD420.
From 0 to 3 volts on the AD420 (6 volts after the amplifier) everything works stably. Increasing the voltage, the output signal starts to somehow jitter (as shown on the oscillogram). I use VLL for power ADUM1401.

Why is this happening?

PS In the current version of this scheme, everything works stably and without problems.

P.S.1 I have a video - DAC AD420 problem - YouTube 

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  • 0
    •  Analog Employees 
    on Aug 11, 2017 12:44 PM

    Hi Nevox,

    Looking at the oscilloscope shots, a digital signal (high frequency 3.3V) is being coupled to the output.

    How are you connecting the oscilloscope probe? is it across the OUT1 and ground of the gain setting resistors of the amplifier?

    The digital signal can also be coupled through the pull-down resistors connected on your digital lines. can you try measuring the output without the pull-down resistors?

    Can you also send an image of your board layout?

    Best regards,

    Rainier

Reply
  • 0
    •  Analog Employees 
    on Aug 11, 2017 12:44 PM

    Hi Nevox,

    Looking at the oscilloscope shots, a digital signal (high frequency 3.3V) is being coupled to the output.

    How are you connecting the oscilloscope probe? is it across the OUT1 and ground of the gain setting resistors of the amplifier?

    The digital signal can also be coupled through the pull-down resistors connected on your digital lines. can you try measuring the output without the pull-down resistors?

    Can you also send an image of your board layout?

    Best regards,

    Rainier

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