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ADS1120: Regarding Single-Ended Operation

Kyohei
Expert 1701 points
Part Number: ADS1120


Hi team,

I have two questions about using the ADS1120 in single-ended mode.

Question 1

Operating Conditions:

  • Using the ADC in single-ended mode (AVSS connected to AINN, AIN1 set as AINp input)
  • Power supply voltage: 5V (AVDD = +5V, AVSS = 0V)
  • External reference voltage: 4.096V (REFP0 = 4.096V, REFN0 = AVSS = 0V)
  • Gain = 1 (PGA disabled and bypassed)

Question:
When 4.096V, 2.048V, or 0V is applied to AINn (AIN1), what will be the ADC conversion result (output code)?
I believe this can be calculated from the datasheet section "8.5.2 Data Format", but I would appreciate your guidance.

Question 2

Operating Conditions:
Using in single-ended mode
VADD = 5V, VASS = 0V, Vref = REFP0 = 4.096V, REFN0 = AVSS = 0V

image.png

Question:
If -0.1V is applied to AINx, what will be the output code? Will it be 0000h, or a code corresponding to -0.1V?

Best regards,

Kyohei

  • 0
    TI__Intellectual 1090 points

    Hello Kyohei-san, 

    Question 1:

    Yes you are correct expected output code can be calculated in this way.  1 LSB = (2 · Vref / Gain) / 2^16 = +FS / 2^15

    A positive full scale range input, in your case +4.096V, the output code expected would be 7FFFh, 3FFFh would be expected at 2.048V, and you would expect at 0V to have a output code close to 0000h. There might be some device offset that could effect any of those numbers. 

    Question 2: 

    The expected code would be the twos compliment of -100mV since the data format is bipolar. 

    Regards, 

    Andrew