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Original question:

ADS1605: about TUE calculation

DAC8532: Total Unadjusted Error

Darko Kulic
Prodigy 10 points
Part Number: DAC8532

Hej Folks,

I have a little bit a problem interpreting the TUE. I calculated my Error depending on the accuracy of my voltage ref. and all the other characteristics. Now I have some value and I dont know what to do with it.

For example :(with some fake numbers):

My DAC can Output 0V to 5V. 16Bit,  I calculated an TUE of 688LSB ( maximal Characteristics) . So 5V/(2^16 - 1 )  = LSB  = ~76,3 mV  and therefor the TUE_max  = 0.0525 V.

So how do I use the Values now? Can I add this to every Outputvoltage as an Offset? For example I want to give out 3.2 V with my DAC. Is the Outputvoltage I have to expect 3.2V+0.0525V? Is it the same if I give an Output voltage of 5V? So i need to expect an Votlage of 5V+0.0525V?

Another question is, I used only the max values from the datasheet. Do they now refer TA =105°C or Tjunction = 105°C?

What if I want to know the room temp value? Do I have to calculate the value backwards?

maxGain_err - (GainDrift*deltaT(K))  = typGain_err

thank you very much for your help Im a Student and Im doing this for my Bachelorthesis!

BR

DK

  • +1
    TI__Mastermind 18546 points

    Hi,

    Your LSB calculation is wrong.

    with 5V as full scale range, LSB = 5/2^16 = 76uV ( not mV)

    Now coming back to TUE, Total Adjusted Error  = SQRT ( Gain error^2 + Offset error^2 + INL^2)

    DAC8532 Max Specifications :

    INL = +/-0.0987% FSR = (0.0987/100) *5V = 4.935mV

    Gain Error = +/-1% FSR = (1/100)*5V = 50mV

    Offset Error = 25mV

    TUE = SQRT ((4.935mV)^2 + (50mV)^2 +(25mV)^2)

    TUE = 56.3mV

    This error means that at any point in the code, you can expect the output to be deviated within 56.3mV. You can reduce this error by calibrating the offset error and Gain error. INL error cannot be calibrated unless you employ code to code error calculation which is not practical.

    Max values in the datasheet for ambient temperature 105degC. Room temperature values are mentioned in the datasheet which is typical specifications.

    Regards,

    AK

  • 0 in reply to Akhilesh K
    Prodigy 10 points

    Thank you for your fast answer. So I can see it as an offset for every output voltage.

    THANKS ALOT!