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OPA189: Spike occurs when it as a I-V conversion OP after DAC8811 current output

Cindy Chang
Intellectual 2475 points
Part Number: OPA189
Other Parts Discussed in Thread: DAC8811, , DAC8801

Hi,

We found that overshoot and undershoot can be observed from the output pin of OPA189 when it as a I-V conversion OP after DAC8811 current output. (Yellow waveform below)

We’ve went through the datasheet of OPA189 roughly but didn’t see any paragraph mentioned about output resonance.

We replaced R8 from 2K ohm to 47 ohm and added an additional 11K ohm resistor in parallel connection with C3.

The blue waveform in the figure below is what we measured from the output of RC filter, and yellow waveform is without RC filter.

 

The resonance seems to be improved but the settling time is extended.

Do you have any other solution that could help to reduce OPA189 output resonance without settling time extended?

Thanks for your kindly support.

Best Regards,
Cindy

  • 0
    Guru 140200 points
    Hi Cindy,

    section 8.3.1 of datasheet of DAC8801 recommends the add of a compensation capacitor (C1). This cap would provide a phase lead compensation and by this decrease the ringing.

    Decreasing R8 to 47R and leaving C3 at 470pF can additionally destabilize the OPAmp. So, either you increase R8 again or you should decrease (or even remove) C3.

    Kai