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DAC7750: About settling time

Masayoshi Takahashi
Intellectual 1530 points
Part Number: DAC7750

Hi team,

Could you tell me about the settling time of DAC7750?

1. Datasheet mentioned the settling time in condition that 16mA step, to 0.1% FSR. Could you tell me about this condition more detail?

2. The customer would like to know how much the settling time when current is change to 20mA from 4mA and change to 4mA from 20mA. Could you tell me how much the settling time in these case?

Regards,

Yoshi

  • 0
    TI__Intellectual 1570 points

    Hello,

    1. Settling time of a DAC is typically specified to within x% of the final settled value. For this case, the settling is specified to within 0.1%FSR of the DAC. That corresponds to the time it takes the DAC to changed from 4mA reach within 16uA of the final settled DAC current (20 mA).

    2. Typically the settling time for a rising current step and a falling current step are identical, hence the reason why there's only one spec in the electrical characteristics table of the datasheet. However, the typical settling time graphs are shown in the datasheet as well for both rising and falling steps. Please refer to figures 43 & 44 for the DAC7750. The total setting time for a 4-20 mA step immediately followed by a 20-4 mA step will be twice the specified datasheet value.

    Regards,

    Reza

  • 0 in reply to Reza Abdullah
    TI__Intellectual 1530 points

    Hi Reza,

    Thanks for your quick answer. I understood.

    I'd like to ask one more question about TUE (4 mA to 20 mA).

    Datasheet showed 0.25% FSR. 

    When I calculated the TUE by using INL error (0.08%), offset error (0.22%), gain error (0.2%) from the datasheet, max TUE is almost 0.3%.

    Could you tell me how to calculate in the datasheet value?

    Regards,

    Yoshi

  • 0 in reply to Masayoshi Takahashi
    TI__Intellectual 1570 points

    Hello Yoshi,

    The datasheet specifications were obtained from actual test data by directly measuring the test parameter for several devices, doing the necessary statistical analysis across several test conditions, and adding the necessary guard bands to guarantee the minimum and maximum values in the datasheet. 

    For the DAC7750, the TUE was measured directly for each tested unit and not by using the summation of INL, gain & offset errors. The direct measurement is more accurate and does not assume dependencies or lack thereof between different measurement parameters.

    Also, you should note that each parameter is guard-banded separately, (offset, gain, etc) and deriving TUE from these parameters will usually over-estimate the max spec for the device. 

    Hope that helps!

    Regards,

    Reza