• State Resolved
  • Locked Locked
  • Replies 2 replies
  • Subscribers 30 subscribers
  • Views 469 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

TMCS1123: Small current measurement precision and calibration

Ugljesa Tomanovic
Prodigy 50 points
Part Number: TMCS1123

Hello,

My client is considering using TMCS1123 to measure current in the energy measurement circuit of an EV charger. The minimal current in the measurement range is 50mA and the needed accuracy of the energy measurement in that range is 2.5% on the room temperature.
I have two concerns regarding this approach:

1. Offset:
Is it possible to calibrate out the offset in the production? Is the offset for a particular sensor same for a given temperature during the lifetime of a device? Additionally, is the temperature drift a constant that can be determined by measuring the offset on two temperatures during the production?

2. Noise:

The stated input noise density is 150uA/sqrt(Hz), as anti-aliasing filter before the ADC has a bandwidth of 7kHz that would mean that the Irms noise is around 12mA, which prevents us from achieving desired precision. Was my calculation correct?

BR

Ugljesa

  • +1
    TI__Mastermind 26185 points

    Hello Ugljesa,

    Here are my responses to your questions:

    1. Yes, the offset can be calibrated out in production, including across temperature if necessary. Unfortunately, there are no lifetime specs for the offset drift in the available preview datasheet. I am not sure if there will be further information/specs in the production version of the datasheet or not. When the production datasheet is available, it should have a Typical Characteristics plot that will show the offset vs temperature to show if two calibration points will be enough for your system. 

    2. Yes, it looks like your calculation was correct (I'm getting about 12.55mA noise at 7kHz), which will definitely have lower accuracy at 50mA measurements than your goal of 2.5%.

    Regards,

    Mitch

  • 0 in reply to Mitch M
    Prodigy 50 points

    Thank you very much Mitch,

    BR

    Ugljesa