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ads1115 replacement for the ads1100

Gaston_Melo_Arg
Mastermind 7675 points
Other Parts Discussed in Thread: ADS1100, ADS1115

Hi to all,

I was using the ads1100 as single ended to measure and input from 0 to 5V max. Now I have to measure 4 inputs in the range of 0 to 5V (single ended app). I was looking at the ads1115 to perform this task, but I have a few questions:

1) To reach the 5V FS I have to set the PGA reg to 0 (2/3 gain), in this case what is the value of the voltage reference?

3) the output code will be 32768 for the 5V input or the value of the voltage reference?

regards

Gastón

  • 0
    TI__Guru* 97775 points
    Gaston,


    If you need to measure the full range of the supply of 5V, you indeed must put the PGA to the 2/3 range. This will make the reference appear to be 6.144V (this is achieved with scaling of the reference sample).

    If 5V is put on the input with this PGA, the output code will be 682Bh or 26667d.

    Was there another question? You numbered 3 questions, but only asked 2.


    Joseph Wu
  • 0 in reply to Joseph Wu
    Mastermind 7675 points
    yes indeed:
    3) how to calculate the output code? for example pag 6 of ads1100 give the equation to know the output code. Is this similar?
    Regards
    Gastón
  • 0 in reply to Gaston_Melo_Arg
    TI__Guru* 97775 points
    Gaston,


    The calculation is based on the PGA setting. In the case of the PGA = 2/3, the output is given as:

    Output code = (2/3)*(VIN/4.096)*2^15

    In the above equation, I've rolled in the PGA value into the calculation.

    If you look at the datasheet on page 14, it gives the output data format based on the positive full-scale range. If PGA is 2/3, then this value is 6.144V, which gives the same result. The PGA positive full-scale range is given on page 13.

    This is different for the ADS1100, where the input range is based the VDD value, instead of a known reference value.


    Joseph Wu
  • 0 in reply to Joseph Wu
    Mastermind 7675 points
    thanks Joseph.
    Regards
    Gastón