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ADS1115: Power-up sequence

Tran Tuan
Prodigy 50 points
Part Number: ADS1115
Other Parts Discussed in Thread: ADS1015

Tool/software:

Dear Sir,
I have a question about supplying power to ADS1115. If all the digital pins of ADS1115 become active before ADS1115's VDD pin is powered up, is there any risk of damaging the ADS1115? My circuit has 2 power sources for analog and digital separately, and they may turn on at different times.

Sincerely,

Tuan Tran

  • +1
    TI__Genius 14700 points

    Hi Tuan,

    The digital inputs can be supplied while VDD is not powered without damaging the device.

    Regards,
    Joel

  • +1 in reply to Joel Meraz
    Prodigy 50 points

    Hi Joel,
    Thank you for your promt respond.
    Just another question about ADS1015 gain.
    I read a comment in an example code from Adafruit, like this:


    // The ADC input range (or gain) can be changed via the following
    // functions, but be careful never to exceed VDD +0.3V max, or to
    // exceed the upper and lower limits if you adjust the input range!
    // Setting these values incorrectly may destroy your ADC!

    Why setting the ADS1015's gain can destroy the ADC, and how to avoid it?


    Thank you and best regards,
    Tuan Tran.

  • +1 in reply to Tran Tuan
    TI__Genius 14700 points

    Hi Tuan,

    Table 7-1 shows the input ranges of the ADS1015/ADS1115. An input higher than the positive full-scale won't harm the device. Only an input 0.3V above VDD could cause harm to the device to to ESD protection diodes at the inputs. 

    For example if VDD is 5.5V, and the PGA is set to +/-6.144V input range, the maximum input you should apply is 5.8V. You won't be able to use the full input range at the +/-6.144V input range setting since 5.5V is the maximum operational supply voltage.

    Regards,
    Joel