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Problem with external VREF AD9629

Hi all,

I have design a board using an ADC AD9629, combined with a differential amplifier ADA4940.
It works fine in normal mode. In normal mode I m measuring single pulses from 0V to 6V to VIN without any issue at 10Msps.
I have used an external reference ADR130BUJZ, in order to compensate the temperature variation of my system.

I have an additionnal DAC (MAX5815) which goes to VIN.  This DAC apply a DC signal to VIN. With this DAC, I can create a lookup table (in my software) to compensate the gain error.

However, am seeing something odd: Whenever i change the DAC value with the ADC clock ON, my external VREF goes from 1V to 0V. Then the Adc is blocked, I have got to unplug my board.

What can create this issue?

AD9629_.pdf
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  • Hi Doug,

    Thanks for your feedback.

    Yes, below my configuration with the DAC...

    My current work around is to stop running the ADC clock, and then change the DAC value and restart ADC. Then I get the correct value. But I don't understand why, the VREF goes to 0V....

    I have made several boards showing the same results.

    +5V_ANA is always good.

    regards

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  • Hi Doug,

    Thanks for your feedback.

    Yes, below my configuration with the DAC...

    My current work around is to stop running the ADC clock, and then change the DAC value and restart ADC. Then I get the correct value. But I don't understand why, the VREF goes to 0V....

    I have made several boards showing the same results.

    +5V_ANA is always good.

    regards

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