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ADS1015: part failing with unused inputs in a 24v system

Scott Daniels
Prodigy 70 points
Part Number: ADS1015

Tool/software:

We are using the ADS1015 in a 24v industrial control board, but currently, all the inputs are either open or connected to an input pin that is not used. We are getting repeated failures of the part. In some cases, the I2C portion causes the entire I2C bus to become unusable, and in one case a short of the 3.3V supply was the result. While it is possible that someone accidently touched an input pin with 24 volts, it is unlikely. Currently, there is no protection circuitry on the inputs.

1. Is it normal for these kind of failures when there is no input protection circuitry?

2. Will input protection circuitry prevent these failures or is there some other possible cause?

3. What is the recommended input protection?

4. Should unused input pins be tied  to something?

Thanks,

Scott

  • 0
    TI__Prodigy 260 points

    Hello Scott,

    Thank you for your question.  I'm working on it and will get back to you later today.

    Best Regards,

    Henry Sarmiento

  • 0 in reply to Henry Sarmiento
    TI__Prodigy 260 points

    Hello Scott,

    Thank you for your patience.  Answers are shown after your question below.

     

    1. Is it normal for these kind of failures when there is no input protection circuitry?

    Answer: The analog inputs have internal protection diodes to protect against overvoltage.  However, if the analog inputs continue to experience voltages that exceed 300mV, then the ADS1015 can be permanently damaged.  The type of failure seen by the user depends on the extent of device damage, circuit configuration, or application.

     

    2. Will input protection circuitry prevent these failures or is there some other possible cause?

    Answer: To prevent analog input damage, the analog input voltages should be within the range show by equation GND – 0.3 V < V(AINX) < VDD + 0.3 V.  To aid in protecting against overvoltage, place current limiting resistors on the input lines that will allow up to 10mA of current.  As a general practice, work inside an ESD safe environment.

     

    3. What is the recommended input protection?

    Answer: Please, see answer to question 2 above.

     

    4. Should unused input pins be tied to something?

    Answer: The unused analog input pins can either float (not-connected) or be tied to GND.

     

    Best Regards,

    Henry Sarmiento