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BQ27427: For 4.5V battery type

Hugo Lee
Intellectual 550 points
Part Number: BQ27427
Other Parts Discussed in Thread: GPCCHEM, BQ27426, BQ27Z746, BQ27Z561

Could we use BQ27427 fuel gauge for 4.5V battery?

Although only up to 4.4V default chemical ID could be selected, it will automatically be updated to 4.5V after we complete a learning cycle, right? 

Technical reference manual mentioned as below:

https://www.ti.com/lit/pdf/sluucd5?keyMatch=SLUUCD5

V at Chg Term will automatically be updated and learned by the gauge during system operation whenever charge termination is detected. It represents the full charge point for a given system which can vary from charger to charger and also depends on temperature and other factors.

at [7.4.4.1.2 V at Chg Term], that value has the range from 0 to 5000mV.

Thanks, 

  • 0
    TI__Guru** 105770 points

    Hello Hugo,

    You will not be able to use a ROM gauge (like the BQ27427 or BQ27426) with a battery that charges to 4.5V. The preset chem IDs that come with the gauge are only characterized for the specified max voltage, if you go over the voltage it will saturate at the 4.4V and potentially cause gauging error. If you plan to charge to 4.4V with your cell which is rated for 4.5V you may be able to use a ROM gauge but I would recommend using the GPCCHEM tool to make sure it will still match decently well with the 4.4V chem ID.

    Sincerely,

    Wyatt Keller

  • 0 in reply to Wyatt Keller
    Intellectual 550 points

    Hi Wyatt,

    Base on [Figure 2-1 Power Mode Diagram] in https://www.ti.com/lit/pdf/sluucd5  BQ27427 Technical Manual
    ROM data will be copied to RAM, and host seems can change RAM and NVM based data blocks at POR initiation procedure, right?


    Could we set proper  value of "Primary Charge Termination" [Taper Rate, Taper Voltage] corresponding to 4.5V battery chracteristic] to improve gauging error?

    Could this gauging error for 4.5V type battery be covered and improved by several fuel gauge learning cycle?


    To understand more about BQ27427 gauging error for 4.5V type battery ->  Which data will be saturated before meeting "Primary Charge Termination" at [Table 7-2 Data Flash] in BQ27427 technical manual https://www.ti.com/lit/pdf/sluucd5?   


  • 0 in reply to Hugo Lee
    TI__Mastermind 25021 points

    Hello Hugo, 

    If you are using this gauge with a 4.5V cell, then you will not be able to charge all the way up to 4.5V. To use this gauge with this cell you would first have to use the GPCCHEM tool to make sure that the 3142 ChemID (4.4V ChemID from gauge) is a good match for your cell. If the ChemID is a good match for your cell then you can use this gauge, but you will only be able to charge your cell up to a maximum of 4.4V. In doing this you will be losing some capacity from your cell as you will not be charging up to the full 4.5V. If your application requires you to charge your cell to the 4.5V, then I would recommend using another gauge such as the BQ27Z746 or the BQ27Z561.

    Regards, 

    Jonny.