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RTIA, Calibration and Current

Category: Software
Product Number: AD5941

Hi, ADI Support.

I am having an issue with the AD5941, the problem I am facing is that when changing the RTIA (Gain Resistor) I am getting very different currents. I have noticed a ratio of 0.6 from the currents observed with the 1K and 200 Ohm gain resistors.

I am changing the code before initialization, not during the measurement. I have checked the currents with a multimeter and it is approximately the same as when I am using the 200 Ohm gain resistor.

Could you give me any insight into why this may be happening?

So essentially I would like to know if I should be observing the same current when switching Gain Resistors (RTIA) or should I see a reduction in current when moving to higher Gain resistor?

Thanks in advance.

  • Hi,

    Input to ADC of AD5491 = input current X RTIA

    This ADC input must be within +/-900mV (for PGA gain = 1 or 1.5)

    - As long as this input is within allowed range, there won't be any change in current measurement output with change in RTIA value.

    - If this input goes out of range (by changing RTIA value), output deviates due to saturation and hence gives different current output value which is not the actual input current value.