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DAC8750: about current output accuracy

Noriyuki Takahashi
Genius 11470 points
Part Number: DAC8750


Hi team,

We are struggling to understand why there is a difference between the measured current output and the assumed current output.

We assume that the current output accuracy is within +/-0.18%FSR. How to get the number is below.

TUE = +/-0.08%FSR, Internal voltage reference = 5V +/- 0.1%

Therefore, the accuracy = +/-(0.08 + 0.1)% = +/-0.18%

At 24mA output range, the output would be 24mA * +/-0.18% = +/-0.0432mA

(I am not confident with this calculation is true..)

Then, we tried 3pcs of DAC8750 by EVM and found that one output is 4.0480mA and others are 4.0100mA and 4.0210mA.

So, 4.0480mA is out of our estimation. Could you come up with why this is?

Regards,

Noriyuki Takahashi

  • 0
    TI__Expert 5820 points

    Hi Noriyuki,

    I agree with your estimation of the worst case error based on the reference tolerance and TUE of the current output. Since you used the min and max values I would expect in measuring across several devices it would be much closer to the typical value for TUE. We typically use the root sum of squares to approximate the error if the error sources are independent.

    Are you using the external NPN transistor in the 'boost mode configuration' as seen in Figure 56 of the datasheet? This mode is selected on the EVM by JP5. Using the external transistor will create additional gain error as shown in Figures 15 through 17 in the typical characteristics section of the datasheet.

    Are you using external or internal Rset? Using the external gain setting resistor also contributes to the overall error.

    Thanks,

    Garrett