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ADS1115: 16bit resolution does not add up

Mike Kopp
Prodigy 10 points

Part Number: ADS1115

Hi,

I am using a voltage divider to measure the voltage drop on an ohmic resistor (0V-5V)(NTC). When I take out the sensor I should get a steady 2^16 output (bc 16bit resolution). However the ADS1115 gives me a value of 26753 (give or take). It varies +/- 10 data points. Why is that and what am I doing wrong?

I’m sending the data from the ADS1115 to an Arduino Mega. The voltage divider is supplied by the Arduino (5V).

Thank you so much in advance.

  • 0
    TI__Guru** 101045 points
    Mike,


    The ADS1115 is a fully differential ADC and even if the device is used as single-ended, the ADC data is still measured differentially. Because of this, the positive full scale is 2^15-1 (7FFF).

    For your measurement, I would guess that you're using the ±6.144V FSR range. If you're getting 26753d, this would convert to:

    (26753*6.144V)/2^15 = 5.016V.

    That would be pretty close to the 5V that you would have expected. I would note that in the ±6.144V range, the input wouldn't go full scale because the input voltage is still smaller that the full scale. Note that the input shouldn't go beyond the supplies. The maximum absolute input voltage is VDD+0.3V and going beyond that may risk damage to the device.


    Joseph Wu