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TMCS1108: TMCS1108A1BQDR

Ali Khan
Intellectual 970 points
Part Number: TMCS1108

Hi,
I am using TMCS1108A1BQDR and I need help in calibration of the sensor.
Unfortunately, the application was unidirectional and i choose Bidirectional but it isn't a big problem
I am getting following output
1: 2.49 to 2.51V for 0A or no Load
2: 2.54V for 1A

and so on, just add 50mV per ampere as the sensitivity of this sensor is 50mV/Amp

Now, I want to know, how i can measure the current in between 0 and 1A because it keeps generating same output voltages until it reach to 1A. It probably the resolution of this sensor and here it might be another wrong choice that i made(but not sure)

Is there a way that i can monitor current in between 1A resolution?

I have to measure the current upto 10A and I am using Arduino UNO for now to read analog signal.

Thanks

  • 0
    TI__Mastermind 22315 points

    Hello Ali,

    Thank you for using the TI forum. As you suspected, the device variant you are using is not the most ideal for this situation. I recommend using the TMCS1108A4U, which is a unidirectional sensor that will utilize more of your full scale range and have a higher gain making it easier to read low currents. 

    Regards,

    Mitch

  • 0 in reply to Mitch M
    Intellectual 970 points

    Hi
    Thanks for your reply.
    I need 100mA resolution sensor. Do you think it can do it?
    I selected 50mV/A considering that it is low resolution sensor but the resolution depending on the current that is set at 1A. Even if i use the suggested one, it will still change the signal output after each amp. Correct?
    TMCS1108A4U 400 mV/A –1.12 A → 10.75 A

  • 0 in reply to Ali Khan
    TI__Mastermind 22315 points

    Hey Ali,

    Both sensors change the output linearly based on the current detected, not just in 1Amp increments. The reason you had a hart time seeing levels <1Amp with the A1B version is that the current you were measuring was being lost to noise. Switching to the A4U version will significantly help this for your situation. Your final accuracy/resolution will depend on many factors, including the accuracy/resolution of your ADC. Also, here is an app notes that you may find helpful when trying to increase accuracy for this device:

    https://www.ti.com/lit/an/sboa518/sboa518.pdf 

    Regards,

    Mitch

  • 0 in reply to Mitch M
    Intellectual 970 points

    Hi,
    Regarding your noise point. I think, it is not a problem because i am getting 2.49 to 2.50V (0.5 x VS) at 0A.
    When i increase current to 1A then it gives 50mV rise up.
    I will definitely change the IC in next version. Now i have to perform all the required testing with current design board. What steps i should consider so i can get lower resolution at least 0.5A. Also, what is the minimum resolution of this sensor in terms of voltages?
    I couldn't find that value?
    Is it 12bit resolution because i am using 10 bit ADC.


    I read the app notes and they mentioned about 3 major points and checked those. It almost good

  • +1 in reply to Ali Khan
    TI__Mastermind 22315 points

    Hello Ali,

    The voltage will increase linearly with current. So, if you are getting 2.5V at 0A, and 2.55V at 1A, then you should see 2.525V at 0.5A. The voltage output is gained up from the Hall sensor stage, so there is no real minimum resolution, it just outputs a voltage within the datasheet defined accuracy and noise limits. Then it is up to your ADC to get an accurate measurement of the voltage. If you are having a hard time measuring to that accuracy, then you can try taking multiple reads with your ADC and averaging them together. 

    Regards,

    Mitch

  • 0 in reply to Mitch M
    Intellectual 970 points

    Hi
    Thanks for all your help. I am able to reduce it to 300mA. the 300mA create a reasonable change in voltages so i can make decision based on it.
    I was using 50mV in my equation from the datasheet but once i changed it to 20mV, i was able to reduce current.
    One last query before  closing it.
    Can i simply replace the suggested IC on the footprint of this one?
    I belive everything is same. Correct?
    Thanks

  • +1 in reply to Ali Khan
    TI__Mastermind 22315 points

    Hello Ali,

    Yes, if you want to switch to the suggested IC, then you can just swap them out (with the appropriate software changes to account for the different output as well).

    Regards,

    Mitch