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DAC81408: Accuracy for Remote Ground Tracking

ttd
Mastermind 7900 points
Part Number: DAC81408
Other Parts Discussed in Thread: REF3025, OPA2187,

Dear Technical Support Team,

There is Figure 67. Schematic for Remote Ground Tracking on datasheet page 46.

Do you have this accuracy between REFGND PIN and REF PIN?

1kΩ resistor are used in the summing circuit and the non-inverting amplifier. For example, with a 1% non-inverting amplifier, 1+(1.01kΩ/0.99kΩ) or 1+(0.99kΩ/1.01kΩ) would shift 2%, will this also affect the accuracy like 2.5V±2%?

Internal reference range is from 2.4975V to 2.5025V(2.5V±0.1%).

Best Regards,

ttd

  • 0
    TI__Mastermind 18856 points

    Hi ttd,

    You are correct, in saying by adding this additional ground tracking system in place, there will be a compromise in the applied reference voltage.

    But the advantage with this scheme is that as long as you choose resistors with 0.1% tolerance, we can calibrate the entire system for offset.

    if there is significant drift due to offset drift of the op amps, or the REF3025 itself, this solution will become tricky to achieve the desired accuracy. Ultimately system designers need to analyze the signal chain before implementing the scheme. The circuit is just an example how to achieve the remote tracking.

    Hope this helps.

    Regards,

    AK

  • 0 in reply to Akhilesh K
    Mastermind 7900 points

    Hi AK,

    Thank you for your reply.

    In my case, I had chosen the OPA2187 op amp with low offset voltage. When I estimated the overall accuracy, the resistor error had a significant impact,

    so I asked the question. 0.1% tolerance resistors are generally higher cost than 1%, I'd consider it.

    Best Regards,

    ttd

  • 0 in reply to ttd
    Mastermind 7900 points

    Hi AK,

    According to the datasheet 300mV offset can be easily compensated in software.

    DAC81408 has an OFFSETn Register (Offset = 21h - 22h)), can it be used for 300mV correction applications? In E2E below, it said offset to adjust imbalance in differential mode. If this is not available, is it possible to set the DAC to bipolar and set the code with the offset subtracted on the FPGA side? For example, if I want to get 0V, I should set -300mV on the FPGA side.

    e2e.ti.com/.../3563170

    Best Reagrds,

    ttd

  • +1 in reply to ttd
    TI__Mastermind 18856 points

    Hi ttd,

    Offset register is only applicable in differential mode of operation. You can correct the offset digitally by doing a calibration of the DAC after power up by calculating offset code and subtract/add from the actual code.

    Regards,

    AK