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Original question:

ADS114S08: PGA settings

ADS114S08: No effect of PGA setting in ADS114S08

Jason Fan
Intellectual 1705 points
Part Number: ADS114S08
Other Parts Discussed in Thread: ADS124S08

Hi Experts:

My customer is using the ADS114S08 with TC for the temperature measurement , the schematic is below , ( The /DRDY is floated)

When they change the setting with 03h register(00h to 0A,0B...) , the output is almost the same without change ( the input is 50mV, the output is 50mV as well),

The output is the same as the input even they adjust the input from 40mV ~80mV . Additionally, they the value they read from the register is the same as their setting.

The input offset is 1.2V ,and they used the internal reference which is 2.5V.

Please help to check the issue why the PGA setting doesn't take effect in this project.

  • 0
    TI__Guru** 113765 points

    Hi Jason,

    The output code will always reflect the input voltage, so I'm not totally clear on the issue being seen.  For example, if you change the gain from 1 to 2 the output code will increase but will still reflect the value of the input as the full-scale range decreases with applied gain.  If you apply 50mV you will still see 50mV on the output at a gain of 2 and not 100mV as the output code is referred to the input.  What actually happens is the full-scale range decreases.

    To help me better understand, can you give me all of the register settings being used?  Has the customer verified the communication by both reading back the registers and also verifying the communication by oscilloscope or logic analyzer?

    Can you verify whether the device is the ADS114S08 as the schematic is showing ADS124S08.  Is it possible to send me the raw data (unconverted to volts) for me to analyze at the various gains being used?

    Best regards,

    Bob B