Hi everybody,

I have some questions regarding the ADuCM355. We want to use this device for several measurements. That’s why we will use the MUX for the TIA.

•  Low Power RTIA: Accuracy
• Does it mean that if we move from one gain to another gain, that the difference between these gains have an error of -0.6% to +0.6%?
• Or is it just another error which we have to add to the accuracy error?
• On page 8 in the datasheet the value for the accuracy is -5% to +15%. What does that mean in regarding of the comment?
• Does it mean that every single value of the gain can vary by -5% to 15%? Which counts for a chosen resistor setting in the range of 1kOhm to 512kOhm.
• And then, what does the mismatch Error mean?
• Do you have a recommendation how to measure or evaluate these errors? Is there a recommended test schematic or evaluation procedure?
• If not, then we should set the input to a known reference and then just start switching the mux or not?

best regards

Bastian

• Hi Bastian,

The -5/+15% accuracy refers to the initial accuracy of the resistor to its expected value. For example, if you select the 10kohm setting, the worst case values at 25C across any part you receive is 9.5K to 11.5K.

The +/- 0.6% gain mismatch is the error introduced if you change the TIA gain resistor value. So, if you are using the 10K resistor and increase to the 20K resistor, the difference in measurement is +/-0.6% (worst case) - typically its +/-0.2%.

But note, we provide calibration routines that allow you eliminate these error sources.by generating a calibration current across the external calibration resistor (RCAL).

Regards,

Mike

• Dear Mike,

I hit the problem of low accuracy of the low power Rtial resistor.

I believe that it was foreseen to be calibrated via register ADCGNLPTIA0.

However, how to perform calibration procedure? With contrast to high power TIA, the low power TIA circuitry doesn’t have possibility to switch to external Rcal according to schematic from user manual: “Figure 16. Low Power TIA, Low Power Potentiostat, and Low Power DAC Switches for Channel 0”

Thus, your comment is only trye for HPTIA “we provide calibration routines that allow you eliminate these error sources.by generating a calibration current across the external calibration resistor (RCAL).”

Please provide documentation or example how to perform calibration of low power TIA gain resistor.

Regards

Bemben