TLA2022: making sense of the bipolar voltage limits vs single sided supply

Dave Rentoul

Part Number: TLA2022

Tool/software:

My question is with regard to VDD verse the FSR (full scale range). The text in section 8.3.3 says that with Vdd = 3V3 and FSR set to plus/minus 4.096V, only signals up to 3V3 can be measured.

Question: how can it measure a plus/minus 2.048V signal when the supply is signal sided 3V3? Would it not only read plus/minus 1V5? or does the device generate its own negative rail that is not shown in the datasheet?

My plan is to TLA2022 for AC current measurement. I want to determine the CT burden load to maximize my resolution into the ADC. This bit of confusion on how this IC works with regard to range and rail voltages results in a half/double issue on the burden resistor values. Not hard to fix on my prototype, but better if the load is correct straight off the production line.

Thanks for your help,

8 months ago

0 Angel Rodriguez de San Miguel Bermudez 8 months ago

TI__Expert 8140 points

Hi Dave,

The TLA2022 cannot measure negative voltages with respect to GND, as it does not support Bipolar power supplies.

Instead, the negative output codes represent a negative differential input signal, when the absolute voltage at AINN is Higher than the absolute voltage at AINP.

Since Vdiff = AINP - AINN, if the absolute voltage with respect to GND at the AINN pin is higher than the absolute voltage at the AINP pin, then the Value of Vdiff is negative, and this is represented as a negative binary output code from the ADC in binary two's complement format.

The voltages at AINP and AINN however, must be positive with respect to GND.

This is explained in more detailed in the following FAQ: (+) [FAQ] Can my ADC measure negative voltages? - Data converters forum - Data converters - TI E2E support forums

Best Regards,

Angel