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Current Sensing

Alexandre Imbeault
Prodigy 100 points
Other Parts Discussed in Thread: BQ20Z65

Hello, I'm currently working on a battery management system and I'm trying to find the best solution for high precision current sensing. This is used to calculate the State Of Charge (SOC) of battery. I'm looking for a shunt system. My critical specifications are: measuring range of +/- 300A, input voltage up to 100V, operating temperature from -40°C to 125°Cand a high reading precison. If I could read at 100mA precision, I would be really happy, but I need this precicion on entire measuring and temperature range.

I've already looked at shunt current monitor (bi-directionnal), but the most of them are high side and do not respect my input voltage specification. Also, they are getting bad precision with the temperature variation. I also want to make sure that I'm not going to read noise when a 100mA flows into the circuit. That is an other problem of current monitor, they have a offset drift that changes with the temperature and that is bad for me. Maybe it is preferable to build our low side shunt current sensor than use a shunt current monitor ...

I've also looked at hall effect current sensor but I won't get the accuracy I need. I think shunt is the best solution.

Can someone help me finding out a good solution for my problem?

Thank you

  • 0
    TI__Mastermind 36110 points

    You have a difficult problem. 100mA/300A = 0.03%.  I do not think TI has a technology that will make this measurement for you.  You might need to consider having multiple power paths, each with a different current sensing element that is chosen to provide the best resolution at the path's maximum current.  This is much like a current meter that switches between scales (different internal measurement circuitry) as the current changes.

  • 0 in reply to Matthew Day
    Prodigy 100 points

    Do you think it is possible with a shunt current monitor on low side? Or maybe with a instrumentation amplifier with a shunt resistor on low side?

    The reason of the low-side is that I have up to 350V on high side and there is no device I found that can support that voltage.

  • 0 in reply to Alexandre Imbeault
    TI__Mastermind 36110 points

    Yes, it should be possible.  You will need to be careful about your grounding.  The voltage potential will be different depending on whether you measure with respec to one side or the other of your sense resistor.

  • 0 in reply to Matthew Day
    Intellectual 425 points

    Hi,

    I'm using a bq20z65 and a 5mOhm sense resistor and I'm wondering about the necessity of the calibration. Is it compulsory to calibrate each new PCB if we use the sense resistor of 5mOhm 1% tol. ?

    In SLUA391, the flow diagram presents the step of calibration for each product. But is that not possible to flash each PCB with already the calibration data ? If we can assure that the sense resistor is 1% tolerance, is  a calibration still obligatory ? What is the effect on the state of charge ?

    Thanks,

    Alex