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ADC12D1800: ADC12D1800

michael modilevsky
Prodigy 20 points
Part Number: ADC12D1800

Hi, I'm using ADC12D1800.  connected vbiasq and vbiasl to ground with 100nF capacitors as recommended. Check voltage on the caps and it shows -0.9v , negative voltage. While my input voltages  of the ADC are positive.

Checked datasheet and no circuit of the VBias pins. On what voltage does the Vbias depend and what may cause the negative voltage?

Thanks

  • 0
    TI__Mastermind 20130 points

     Hi Michael,

    It would be difficult to tell if there is an issue with your board design which I assume you are taking the measurement from.

    There is no way to generate a negative voltage bias internal to the device which is being seen on the board.

    Is it possible that one of the caps to ground is shorted to some other supply voltage on the board instead?

    Regards,

    Rob

  • 0 in reply to Rob Reeder
    Prodigy 20 points

    Hi Rob,

    I understand that its difficult to answer this question without seeing the board and the design.

    This is a one card of many that works.

    On a working card I see that the vbiasq and vbiasl are 0V.

    That is why I asked if i can get more information about the pins vbiasq and vbiasl to understand where do they get their voltage from and what can effect them.

    Thanks,

  • 0 in reply to michael modilevsky
    TI__Mastermind 20130 points

    Hi Michael,

    Can you please confirm that you are saying that for a good board you are measuring 0V on the Vbiasq/l?

    And on a bad board you are measuring -0.9V?

    I spoke to design today and -0.9V should be correct. I was in error there is a neg charge pump circuit inside the IC, so plan to measure this in the lab tomorrow to confirm.

    Also, in the meantime, if you send me a schematic for me to quickly review this might help as well.

    Regards,

    Rob

  • 0 in reply to Rob Reeder
    TI__Mastermind 20130 points

    Hi Michael,

    I measured an evaluation board in the lab today.

    Both VbiasQ/L pins are -0.9V.

    Power must be applied to the converter as well as a clock signal.

    Otherwise, the negative charge pump circuits will not necessarily be at that voltage.

    Regards,

    Rob