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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?