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TMCS1123: Measuring alternating current

Part Number: TMCS1123
Other Parts Discussed in Thread: INA3221, , INA228, AMC131M03, TMCS1100

I was advised to use TMCS1123 to measure alternating current when using TEC controller for peltier cooling. Voltage changes from -15V to +15V or actually polarity of voltage changes depending on heating or cooling. Current stays under 5A. I want to measure also the voltage in addition to current. I was advised to use Texas instrument ADC that also include I2C communication. I have used INA3221 to do this whole thing when polarity does not change but now I have issue with changing polarity and that's why I am forced to use other method. Is this possible?

  • Kimmon,

    You could use this application note: and using the -15V supply if you have it to use similar to the -48V in the applicaiton note. with a digital current sensor like the INA228 or any of these device that have VCM ability above 30V.

  • Hello Javier,

    Thank you but im not sure if i can use that application.

    I am using this peltier controller:

    Load is few peltier elements in series.

    At first polarity can be right but after 5min it can change to reverse. Its because peltier will heat at first amd when we reach desired temp polarity will reverse and peltier will cool and try to keep that temp. Voltage over peltier is 15V. 

    It would be easier to use hall sensor because it can handle reverse voltage and can be use to measure alternating current. Any comment on this?

  • Hello Kimmon,

    Given that you are only trying to measure 5A max, you could consider the TMCS1100A4, which is a hall-effect current sensor similar to the TMCS1123, but is made for lower current values. Is there a particular reason you wished to use the TMCS1123?

    The downside to using our hall-effect current sensors is that they will require you to use an external ADC with the part as we do not currently offer any digital Hall effect current sensors. In addition to Javier's suggestion using our discrete current sensors with isolation parts, we also offer isolated current sensors , however these parts use SPI instead of I2C. There are also Isolated amplifers that you could use with an ADC.

    Let me know if you have any questions about these options,

    Levi DeVries

  • Hello Levi,

    There is no real reason to use that sensor.

    I have a larger device and i use multiple INA3221 sensors to read currents and voltages. In this part of the device it's not possible to use INA3221 because of that negative voltage. I tried and chip burnt. That is why i want to replace INA with other working sensor. I use i2c for communication.

    Is it possible to build that isolation for INA3221? 

  • Hello,

    I don't think it is possible with the INA3221. The INA3221 only tolerates voltages up to 26V, so even if you used a digital isolator to communicate with the INA3221 and had a power supply on the isolation side to set the INA3221's GND level to -15V you would still be only be able to tolerate 11V max, so the voltage measurement would be out of your reach.

    I would recommend you look at the AMC131M03 part first as it may be the only device you need. The biggest caveats I see with using this device are that you will have a limited measurement range and you will need to use SPI. The measurement range may not be an issue if you are only measuring current, but will not allow you to measure voltages.

    The TMCS1100 can also measure these currents, and is probably simpler to use, but it is only a single-channel device and you will need an external ADC to digitize the data. 

    Let me know if you have any more questions about this,

    Levi DeVries