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ADS1219: Relationship between INL and LSB

Koji Hayashi92
Mastermind 7030 points
Part Number: ADS1219
Other Parts Discussed in Thread: ADS127L21B

Tool/software:

Hi,team

I would like to know how much INL varies based on 1LSB.

The LSB size of the ADS1219 is 244.14nV when using an internal VREF of 2.048V and a Gain of 1.
It says that the INL is a maximum of ±15ppm FSR.
In this case, there is an error of 15ppm of 2.048V, which means

2.048V x 15ppm = 2.048 x 0.000015 = 30.72uV

and I understand that there is a shift of 126LSB, but is this correct?

Also, if an external VREF is used, is it correct to use
External VREF x 15 ppm?
For example, if the external VREF is 4.5V, then 4.5V x 15ppm

Best Regards,
Koji

  • 0
    TI__Guru 52496 points

    Hi Koji Hayashi92,

    To clarify, the title of your post references the ADS1219, but the text in your post references the ADS1216. Can you tell us which device you are referring to?

    Koji Hayashi92 said:
    and I understand that there is a shift of 126LSB, but is this correct?

    Yes, your understanding and calculations are correct

    Koji Hayashi92 said:
    Also, if an external VREF is used, is it correct to use
    External VREF x 15 ppm?
    For example, if the external VREF is 4.5V, then 4.5V x 15ppm

    Yes, this is also correct

    -Bryan

  • 0 in reply to Bryan Lizon86
    Mastermind 7030 points

    Hi Bryan,
    Thank you for response.

    Sorry for the mistake in the description.
    This is about ADS1219.

    This means that the INL will be quite off, but is this unavoidable when it comes to a 24-bit ADC?

    Best Regards,
    Koji

  • +1 in reply to Koji Hayashi92
    TI__Guru 52496 points

    Hi Koji Hayashi92,

    Generally the INL is not the largest error for an ADC anyway. See the first image below from the ADS1219 datasheet. Note that the typical gain error 0.01%, or 100ppm. This error is significantly larger than the INL, though the gain error scales with input signal while INL does not e.g. at near-zero input voltages the INL error (and offset error) will in fact dominate

    Also, 24-bit ADCs can have very good INL. Below is the INL data for the ADS127L21B. You can see the INL performance is much better compared to ADS1219, even though both are 24-bit ADCs. The INL performance really depends on how much time we spend characterizing and correcting for INL in development, as well as how much we test for INL in production. More testing results in higher cost to build, so for lower-cost devices like ADS1219 the INL tends to be higher. If you want a higher accuracy ADC it will cost a bit more

    -Bryan