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Selecting between BQJunior (272xx) and Impedance Trak (275xx)

Alex Gutica
Prodigy 70 points
Other Parts Discussed in Thread: BQ27501, BQ27210, BQ27510, BQ27541, BQ27500, BQ27541-V200

Hi,

I am interested in knowing what a decision between the two technologies should be based on?

What is the real world performance difference I should expect between the 272xx and 275xx?

Does one gas gauge work better in certain conditions/with particular chemistries that the other? Does one perform better in certain applications?

 

Thank you,

Alex

 

 

  • 0
    TI__Intellectual 2100 points

    Alex,

    Thanks for asking!  First, here is the breakdown of the technical differences between the 2xx (bqJunior) and 5xx (ImpedanceTrack) gauges. 

    The Junior gauge is really a coulomb counting gauge, meaning that it integrates the voltage across its current sense resistor to determine the total charged passed.  It also has  an "end of discharge" voltage at which it automatically resets itself to 0% state of charge.  To better match the nonlinearities of battery chemistry, it has a few different parameters that compensate for varying temperature and discharge rates.  That having been said, these are really just first order approximations. 

    Junior is our "low cost" option, but also has a few additional advantages.  It is easy to configure and is compatible across all lithium chemistries.  On the other hand, the gauge has difficulty matching battery performance at extreme temperatures and load conditions.  In addition, there are issues with measuring leakage currents that are larger than battery self-discharge, but lower than the sense resistor can detect.  Finally, the gauge will not modify its model as the battery ages, so gauging accuracy decreases as the cell ages.

    The IT gauge addresses all of these issues.  It combines coulomb counting, voltage measurement, and battery impedance measurement to determine exactly how much capacity you have remaining.  The gauge continually learns battery parameters, so the gauge will remain accurate as the battery ages.  In addition, temperature and load compensation are much more accurate.  The tradeoffs for this gauge are driven by cost and complexity.  Because of the complexity of the algorithm, the IT gauge requires more configuration ramp-up time. 

    If you can give details about your application, we can walk through what the specific engineering trade-offs would be.

    Thanks,

    Charles

     

  • 0 in reply to Charles Herder
    Prodigy 70 points

    Hi Charles,

     

    Thank you for your response. I have purchased the two evaluation kits (BQ27501, BQ27210) and I would like to compare their performance side by side. The battery capacity range I am interested in is 1500-2500mAh. These batteries are not naked cells - is it important that I remove the protection circuitry?

    It is not very important what make and manufacturer battery I choose, I would like to choose a battery that works well with these fuel gauges. Do you have specific recommendations?

    The BQ27501 evaluation software comes with a number of predefined chemistries - should I perform a chemistry select cycle even if I am using one of the batteries on the list?

    Finally, do you have a database of parameters for specific batteries for the BQ27210 kit I can use?

    Thank you,

    Alex

  • 0 in reply to Alex Gutica
    TI__Genius 14985 points

    Hi Alex,

    I answered your last question about bq27210 parameters in your other post:

    http://e2e.ti.com/support/power_management/battery_management/f/180/p/81166/285684.aspx#285684

    There is one other important consideration when you think about a bqJunior (like bq27210) and our IT gauges (like bq2750x, bq27510, bq27541).

    The bqJunior is mainly targeted at pack-side applications.  It is usually used inside the battery pack and should always be powered on or else it will forget the information it's learned about the battery, including its current state of charge.  If you have a non-removable pack, then it's almost the same as being inside the pack, as long as you never power it off.  If you use it with removable packs then you will need the host to initialize the bq27210 RAM whenever a new pack is inserted.

    Our IT gauges have flavors that can be used on the system-side.  For example, bq27500/bq27501, bq27510, bq27505, all are designed to expect different packs (even ones with different ages) to be introduced to the system and can handle this swapping quite gracefully.  bq27541-V200 is an example of an IT gauge that is typically used inside the battery pack.

    Regarding your questions about characterizing your batteries with the protection circuitry included: If you are using a system-side gauge then it's fine to do the chemistry selection cycling and learning cycle on the entire pack.  You would probably be okay just manually selecting the chemistry corresponding to your battery in the list, but there might be a better, newer chemID match that was released since then, so it wouldn't hurt to do a selection cycle anyway.  Just be sure to download and run the Chemistry Updater from one of our IT gauging product's webpage to make sure the latest ones are installed.