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ADS1120: Design Requirements

Drake Burtrum
Prodigy 130 points

Part Number: ADS1120
Other Parts Discussed in Thread: ADS1235, ADS112S14, ADS122S14

Hello, I'm looking for an ADC that'll work with a strain gage load cell. The ADS1120 was recommended to me. I plan on testing that with the evaluation board.

I'm wondering about other options though. Is there an ADC with a load cell sensitivity around 1mV/V or lower? Let me know if TI has anything like that. Thank you.

  • 0
    TI__Mastermind 25015 points

    Hi Drake,

    thanks a lot for reaching out with your question and your interest in our ADCs.

    In general most of our ADCs with integrated PGA (programmable gain amplifier) are a good fit for direct strain gauge measurements. The ADC doesn't care about the sensitivity of the load cell in the end. But the right ADC choice depends on your requirements, such as:

    • What resolution do you need to achieve? E.g. how many noise free counts or what effective resolution do you want to achieve?
    • What output data rate do you require? Or what step response are you looking for?
    • Do you have any limitations on the supply voltage range?
    • How many strain gauges do you need to measure? 
    • etc.

    If you have very high resolution requirements, then ADS1235 might be a good option for example.

    Regards,
    Joachim Wuerker

  • 0
    Prodigy 130 points

    I'm sure 8-bit resolution will be enough for what we need. 

    We can go with a lower sample rate as well. 100 SPS should be fine.

    Supply voltage would preferably be around 3V - 3.7V.

    We're only working with 1 strain gage for now. There might be two in the future. 

  • +1 in reply to Drake Burtrum
    TI__Mastermind 25015 points

    Thanks for the additional information Drake.

    You might be surprised, but even achieving 8-bit "noise-free" resolution with a strain gauge that only has 1mV/V sensitivity can be a challenge sometimes.
    Following would be the calculations using ADS1120 with the following assumptions:

    • 3.3V used as bridge excitation voltage and at the same time external reference voltage for the ADC
    • Turbo mode, DR=180SPS
    • Gain=128

    The input referred peak-to-peak noise at those settings according to table 5 in the datasheet is: en_pp = 1.34uVpp.
    The differential output signal of the strain gauge at full capacity would be 3.3V * 1mV/V = 3.3mV.
    Your noise-free counts in that case would be: 3.3mV / 1.34uVpp = 2463 counts.
    This translates to a noise-free resolution of 11.3bits.
    So it seems like the ADS1120 could fit your requirements.

    FYI: We are about to release the next generation of ADS1120 within the next 6 weeks. It is called the ADS112S14.
    You can already find information about it in the ADS122S14 (24-bit version) datasheet.
    https://www.ti.com/product/ADS122S14

    There is also an I2C version available in case you would prefer an I2C interface over SPI.

    Regards,
    Joachim Wuerker

  • 0 in reply to Joachim Wuerker
    Prodigy 130 points

    This helps a lot. Thank you!