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DAC80504: How to output to GND

Yue Chen
Prodigy 41 points
Part Number: DAC80504

The DAC80504 is a rail-to-rail DAC, and its data sheet has its INL test data, and the results show that its INL of 0-65535 is less than 1. After testing, we found that when code<813, the output of 7.3mV has been maintained. Since in extreme cases we require the output to go to GND, we want to find a solution. The manual does specify the output headroom, but I think if TI can get such perfect INL test results, there must be a way to output to GND as well.The third picture is our circuit, I think there should be no use problem.Looking forward to your reply.

  • +1
    TI__Guru 53643 points

    Hi Yue,

    This is a difficult achievement.  We specify our INL down to code 256:

    The main issue is our zero-scale error.  This is the offset on the output caused by our rail-to-rail limitations of the output amplifier.  Now, on most devices you will have good preformance lower than code 256, but you will still have linearity issues near zero code.  The INL plot's first point still probably code 256 or maybe 128. 

    Thinks you can do you improve operation near 0V:

    1. Prevent the DAC from sinking any current on the output.  Current flowing into the DAC output will result in a DC shift.  Near 0V, the op amp is out of its linear operating range, to the output impedance is increasing.

    2. Providing some kind of negative offset on the output.  This could look like a secondary output amplifier stage that has a ~5mV negative offset.

    Thanks,

    paul

  • 0 in reply to Paul_Frost
    Prodigy 41 points

    Hi Paul, 

    Thank you very much for your reply. What you said is consistent with what I thought. It is only because the INL test results in the data sheet confuse me, so I have this question. 

    Yue