• State TI Thinks Resolved
  • Locked Locked
  • Replies 5 replies
  • Answers 3 answers
  • Subscribers 46 subscribers
  • Views 309 views
  • Users 0 members are here
Support feedback
Options
Options
Similar topics

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

Original question:

ADS1118: Value of conversion error parameter for specific condition

ADS1118: How to get value of gain error when FSR=6.144V、Ta=25℃?

Hung Ching Hsu
Expert 3086 points
Part Number: ADS1118

Hi Team

I posted one question about gain error, offset error before as following link.

It's been locked so I open a new thread here. 

Though Joseph told me gain error won't have big change according to the change of FSR,

The customer wants to know concretely how much it deviates from the standard when doing actual machine evaluation.

From the data sheet, it can be read that it has the following characteristic values when FSR: ± 2.048V and Ta = 25 ° C.

・ TYP: 0.01%, MAX: 0.15%

How about the gain error with following condition?  Thanks.

【Condition】
・ Ambient temperature: 25 ℃
・ Power supply voltage: 5.25V
・ FSR: 6.144V
・ DR: 250SPS
・ Input mode: single-end

  • 0
    TI__Mastermind 34991 points

    Hi Hung Ching,

    I reread Joseph's post, it is very comprehensive in terms of the specific plots the customer should look for in the datasheet to get an understanding of how gain error might change with supply and FSR variation

    But the end result is that we do not provide DC characteristic data for all possible permutations of settings, which is why we include the plots in the datasheet. The customer can infer what the gain error might be, but we cannot make any definitive guarantee beyond what is in the datasheet already. I hope this is clear.

    -Bryan

  • 0 in reply to Bryan Lizon86
    TI__Expert 3086 points

    Hi Bryan

    Thanks for the reply.

    From Figure 18, since gain error seems not much change when VDD changes, 

    I would like to explain to the customer from Figure 17.

    Gain error is about -0.01% for customer's condition. 

    Just to make sure, will gain error change when data rate changes?

    Thanks.

  • 0 in reply to Hung Ching Hsu
    TI__Mastermind 34991 points

    Hi Hung Ching,

    I would not expect gain error to have a strong dependence on data rate in the ADS1118 based on char data.

    -Bryan

  • 0 in reply to Bryan Lizon86
    TI__Expert 3086 points

    Hi Bryan 

    Thanks for the reply.

    My customer is wondering how to read figure 18. 

    For FSR: 2.048V, It looks like that as the power supply voltage increases, the gain error become close to  0%.
    Which of the following two points can we tell from this figure?
    ・ Gain error changes in the positive direction as the power supply voltage increases.
    ・ Gain error converges to 0 as the power supply voltage increases.

    Also, does the characteristic at FSR: 6.144V have the same tendency as the characteristic at FSR: 2.048V?

    And is it able to predict that will FSR: 6.144V appear between FSR: 256mV and FSR: 2.048V or under FSR: 2.048V?

    Thanks.

    www.tij.co.jp/.../ads1118.pdf

  • 0 in reply to Hung Ching Hsu
    TI__Mastermind 34991 points

    Hi Hung Ching,

    In looking at Figure 18 in the ADS1118, both plots trend slightly over from 2v to 5.5V. Note that the FSR = +/-256mV plot does not trend toward 0 since it begins at a positive gain error. So I would not believe your first statement is true

    In looking at char data, it seems like most of the FSRs do trend slightly upward (toward a positive gain error), but there is no data specifically for +/-6.144V so I cannot confirm answers to either of your last two questions. I will also restate that this information is provided as-is with no guarantee, and reaffirm that the datasheet is the only source of guaranteed information on this device. The customer can make inferences about a specific set of conditions based on the datasheet plots / values, but they do so at their own risk.

    -Bryan