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ADS774: Linar Error

Y.Ottey
Mastermind 6145 points
Part Number: ADS774

Dear all,

I would like to ask a question about linearity error of ADS774KU/1KE4.

According to datasheet, Linearity Error is ±1/2 like the following picture.


When expressing Linearity Error, other devices use INL and DNL.

How do you calculate the value of “Linearity Error” for this device?

Best Regards,

Y.Ottey

  • 0
    TI__Guru**** 175081 points

    Hi Y. Ottey!

    The ADC774 is a relatively old device from the Burr Brown side of Texas Instruments (circa 1991) and the linearity error in this case would be the same thing as INL that you see in other datasheets.  This is the deviation of the ideal transfer function over the full scale range..  There are no missing codes, but unfortunately I do not have any detail on the deviation of code width, which would be the DNL.

  • 0 in reply to Tom Hendrick
    Mastermind 6145 points

    Hi Tom,

    Thank you for your reply.

    Our customer try to use this device.

    I have been asked about the power supply voltage input to VDD, 2.5V REF, and 10V Range pins.


    In order to meet the specifications such as Linearity Error, what is the recommended power supply voltage noise input to these pins?

    (We think which ripple is desirable, probably not exceeding 1LSB.)

    Best Regards,

    Y.Ottey

     

  • 0 in reply to Y.Ottey
    TI__Guru**** 175081 points

    Hi there!

    The reference stability will have a bigger impact than the supply voltage, but overall 5-10mV of ripple on the supply would be alright.

  • 0 in reply to Tom Hendrick
    Mastermind 6145 points

    Hi Tom

    Thank you for your reply.

    I would like to ask a more question.

    Which pin's power supply voltage noise in the VDD, 2.5V REF, and 10V Range pins affects the INL (Linearity Error) value?

    Which pin's power supply voltage noise has the greatest effect on the electrical characteristics in the data sheet? (In particular, the value of INL)

    Regards,

    Y.Ottey

  • 0 in reply to Y.Ottey
    TI__Guru**** 175081 points

    Hi Y. Ottey,

    Having a solid ground connection and good bypassing to pins 1 and 2 is important.  The 'Layout Precautions' and 'Power Supply Decoupling' sections in the datasheet provide recommendations for best performance of the ADS774.  You may also consider using potentiometers as described in the Calibration section.  If you use the internal reference for anything outside of the ADS774, please consider using adding a buffer on REFOUT.