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DAC80502: Question about zero code error and offset error

Shinichi Inoue
Guru 20361 points
Part Number: DAC80502
Other Parts Discussed in Thread: DAC80504,

Dear Specialists,

My customer is considering DAC80504 and has questions.

I would be grateful if you could advise.

---

DAC80502 datasheet describes offset error and zero code error.

Could you please advise regarding two specs in detail.

(1) Zero code error is considered to be the value of analog output voltage when digital code 0000 is input. Is it correct ?

(2) Offset error is the difference between the ideal value of the output when the digital code is input. Is it correct ?

(3) I don't understand the difference between zero code error and offset error.
Is it necessary to add zero code error and offset error?


For DAC80502,
Offset error is -1.5mVmin　0.5mVtyp　1.5mVmax
Zero code error is -1.5mVmin　0.5mVtyp　1.5mVmax
When entering zero code
Is the error maximum -3mVmin　3mVmax?

(4) The minimum Zero code error and offset error are negative voltages, -1.5mV each.
The output voltage range (Vo) is minimum 0V. It cannot output negative voltage, but what will happen to the actual output?

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I appreciate your great help in advance.

Best regards,

Shinichi

  • +1
    TI__Mastermind 31598 points

    Hi Shinichi-san,

    Please refer to this plot. If the dashed line is the ideal transfer function and the solid line is the real transfer function,

    • The offset error cases a shift in the entire transfer function by a certain offset. It is an error in the b term of the line equation y=m*x + b. This is measured over the linear region of the DAC.
    • Zero code error is the minimum that the DAC can output, usually due to headroom requirements of a unipolar DAC. If the DAC minimum supply is ground, then the DAC output can not output 0V. 

    Zero code error is typically not negative and I think this is a typo in the datasheet. The DAC output will never be negative like you said. If offset error is negative, the plot from above becomes this: 

    The output will remain at the zero code error until the DAC code reaches a point on the real transfer function (solid line) that will output a voltage that is greater than the zero code error. 

    The error is not 3mV max. If the offset error is greater than the zero code error, then the error at zero code is just the offset error. If the offset error is less than the zero code error, then the error at zero code is the zero code error.

    Best,

    Katlynne Jones 

    Best,

    Katlynne Jones 

  • 0 in reply to Katlynne Jones
    Guru 20361 points

    Hi Katlynne,

    Thank you for your reply.

    Your explanation helped me understand better.

    In the datasheet of DAC80502, the zero code error is -1.5mVmin.

    Could I think it is typo?

    Is it possible considering the minimum voltage as 0V?

     

    I appreciate your great help and cooperation.

    Best regards,

    Shinichi

  • +1 in reply to Shinichi Inoue
    TI__Mastermind 31598 points

    Hi Shinichi-san,

    I also think this is a typo. Most other datasheets with a unipolar supply only list a typical and maximum (positive) zero code error. The minimum output could only be 0V because this DAC does not have a negative supply. 

    Best,

    Katlynne Jones 

  • +1 in reply to Katlynne Jones
    Guru 20361 points

    Hi Katlynne,

    Thank you for your reply.

    I understand negative voltage zero code error does not occur when using unipolar.

    I'll share this with the customer.

    I appreciate your great help and cooperation.

    Best regards,

    Shinichi