ADS7142: Inconsistent ADC readings across modes.

Dean Chappell

Part Number: ADS7142

I've just received the BOOSTXL-ADS7142 eval platform and have noticed that the ADC readings are different when run in autonomous mode and i2c mode.

eg. Applying a 2V input on CH0 in i2C mode gives an ADC reading of 2525 but when switching to autonomous mode the ADC value is 2458 - a difference of about 50mV.

Is there any explanation why this be?

over 7 years ago

0 Dean Chappell over 7 years ago

Prodigy 40 points

Is there a minimum output current requirement for the sensor attached to the ADS7142 ADC. (eg. i have a temperature sensor which only output 100uA - is this sufficient?)
What is the input impedance of the ADS7142?

0 Dean Chappell over 7 years ago in reply to Dean Chappell

Prodigy 40 points

On further investigation/reading it appears that the difference in sampling rate between i2c mode and autonomous mode can have quite a significant effect on the ADC reading. I slowed down the sampling rate in autonomous mode by using the low power oscillator and the readings became more similar when switching between i2c mode and autonomous mode.

0 Evan Sawyer over 7 years ago in reply to Dean Chappell

TI__Expert 3175 points

Hi Dean,

Great to hear that you were able to find the solution. Let us know if you have any further questions.

Edit: We have added a graph of analog input current vs. nCLK to the datasheet, which was likely the source of the issue for you.

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ADS7142: Inconsistent ADC readings across modes.