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BQ25820: Designing a Li-Po battery charger with fuel gauge, maybe the BQ27427?

Leif Svensson
Prodigy 40 points
Part Number: BQ25820
Other Parts Discussed in Thread: BQ27427, , BQ27441-G1, BQ40Z50-R2, BQ27Z561-R2, BQ40Z50, GPCCHEM

Tool/software:

Hi,

I'm trying to design a single cell Li-Po battery charger using the BQ25280 since I want the high voltage capability. In this application I will use 12V - 36V input for charging and no reverse voltage feed. I also need a fuel gauge and have found the BQ27427 which I think should work here. I still haven't figured out how to connect it all. The charger is rather complex for its task but I haven't found any alternative. Could you please guide me to how to solve this puzzle? Thanks in advance!

B.R.

Leif Svensson,  HW engineer

  • 0
    TI__Mastermind 27405 points

    Hello Leif,

    This battery gauge (BQ25820) may not be suitable for this application due to the max capacity of this gauge being 8000 mAh, if you can provide me the battery cell datasheet and the intended application I can give you my best recommendation.

    Thank you,
    Alan

  • 0 in reply to Alan Frias
    Prodigy 40 points

    Hello Alan,

    Thank you for your answer.
    I have ditched the BQ25820 battery gauge because it only comes in BGA packages. I now will try to use the BQ35100PW or PWR. My battery data is as follows:

    • Chemistry: Lithium Polymer (LiPo)
    • Capacity:     3000 mAh
    • Charge voltage:  4.2V
    • Nominal voltage: 3.7V
    • Turn-off voltage: 3.0V
    • Max charging current: 3000 mAh (1C)
    • Max discharging current: 6000 mAh (2C)
    • Charging temperature: 0°C to +55°C
    • Working temperature: -20°C to +55°C
    • Dimensions: 65 x 36 x 10 mm

    It doesn't contain any temp sensor but I plan on using a 103AT-2 which is recommended in the BQ25820 datasheet.
    I intend to use it in a handheld remote control containing a display, bluetooth chip, a small keyboard etc...
    A goal is to keep it small and not to expensive.

    Best Regards
    Leif Svensson

  • 0 in reply to Leif Svensson
    Prodigy 40 points

    Hello again,

    Sorry, I just discovered that the BQ35100PW is for primary Lithium, i.e. non-chargable batteries...
    Maybe the BQ27441-G1 would work?

    B.R
    Leif S

  • 0 in reply to Leif Svensson
    TI__Mastermind 27405 points

    Helllo Leif,

    Thank you for the cell information and the intended application of the battery gauge based but based on your requirement I would push you to BQ27Z561-R2 however this IC is a BGA package. But if you would a battery gauge without BGA package than I would also recommend would be BQ40z50-r2, the real biggest difference would be price since both use the same battery gauge algorithm.

    Thank you,
    Alan

  • 0 in reply to Alan Frias
    Prodigy 40 points

    Hello Alan,

    Thanx again for your support!
    Is there a reason for NOT using the BQ27441-G1? It seems smaller, cheaper and not as "complicated". I believe my battery pack already contain safety circuits for OVP and UVP.

    However, the original question still remains: How to connect it together, whether I use a BQ40z50 or a BQ27441-G1?

    I find it quite odd that there is no single circuit for both charging AND fuel gauge ?! That would certainly simplify things ;-)

    Regards,
    Leif S

  • 0 in reply to Leif Svensson
    TI__Mastermind 27405 points

    Hello Leif,

    The biggest reason would be due to the BQ27441-G1 not having the entire access to the chemID library, it has a smaller library of the most common chemID's for cost saving measures. ChemID is a cell characterization that allows the battery gauge to run simulation on your cell and the chemID to better predict your State of charge. If you run a GPCCHEM report that selects you chemID and it gives you a chemID that is less than 5% difference (3% is preferred) than it would be the better option. Also you are right that this gauge is the simple and easiest gauge to up bring from start to finish.

    GPCCHEM report:
    https://www.ti.com/tool/GPCCHEM

    Thank you,
    Alan

  • 0 in reply to Alan Frias
    Prodigy 40 points

    Hello again Alan,

    One simple question: If i use the BQ27441-G1 fuel gauge together with the BQ25820RRVR charger, will this work? 

    I very much like the simplicity of it and its small footprint. I don't need super accuracy. I just need to get it done and be able to present a SOC value on the display.

    B.R.

    Leif S

  • +1 in reply to Leif Svensson
    TI__Mastermind 27405 points

    Hello Leif,

    The charger should work with the battery gauge, the main thing that the battery gauge cares about is the current going in and out of the cell meaning it is versatile with many loads and chargers.

    Thank you,
    Alan