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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 CrazyFrog,

    • To confirm, are you saying that the output of the ADR130 goes to 0V when you change the DAC value, with the ADC clock running?
    • If the ADC clock is not running, do you see the same thing happen on VREF? Of course, the ADC will not work without the clock.
    • There seems to be some interaction with the DAC and ADR130. Do you have a schematic that includes the DAC?
    • When VREF_ADC goes to 0V is +5V_ANA still at 5V?

    Thanks,

    Doug

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  • Hi CrazyFrog,

    • To confirm, are you saying that the output of the ADR130 goes to 0V when you change the DAC value, with the ADC clock running?
    • If the ADC clock is not running, do you see the same thing happen on VREF? Of course, the ADC will not work without the clock.
    • There seems to be some interaction with the DAC and ADR130. Do you have a schematic that includes the DAC?
    • When VREF_ADC goes to 0V is +5V_ANA still at 5V?

    Thanks,

    Doug

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