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Question about reading instantaneous discharge current with gas gauge devices

Ray Henry
Prodigy 80 points

Hello!

I am interested in using one of your fuel management ICs (especially, e.g. bq27530) in a new project. I would like to have the normal fuel gauging functions provided.

However, I am interested in also reading the instantaneous DISCHARGE current (by an ADC reading of the sense resistor) at a periodic rate as part of the overall system application.

Using one of these IC's, is it possible to:

1) Cause an ADC reading over the serial bus and get an measure of the discharge current?

2) What is the maximum rate at which these readings would be able to occur over the serial interface (limited by ADC conversion rate + SPI speed, etc.)?

Thank you for any help,

Ray

  • 0
    Guru 22270 points

    Hello Ray,

    It would be much better to get a reading directly from the fuel management ic through i2c. http://www.ti.com/lit/pdf/slua467.  I can't verify yet if this chip provides that information.  You could do a search to see which one of the bq devices does this.  It would eliminate one element from your design.

    Thanks,

  • 0 in reply to Greenja
    Prodigy 80 points

    Thanks, greenja,


    I have looked at several of the devices and they do indeed have readings over I2C.  It is too slow for my application, however - the maximum update rate specified is 1 second for all of the parts that I have looked at.

    I will keep looking.....

  • 0 in reply to Ray Henry
    TI__Genius 14985 points

    Most of the fuel gauges report both AverageCurrent( ) and InstantaneousCurrent( ) but both values are only updated once a second.

    The AverageCurrent( ) is calculated once per second by accumulating the integrated charge from the coulomb counter and dividing by one second.  The coulomb counter is essentially a continuously integrating ADC.

    The InstantaneousCurrent( ) is a single sample from the ADC once per second.

    If you want continuous readings of instant current you might consider using a current shunt monitor, like one of the INA1xx or INA2xx products.