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BQ27621-G1: How to Set Full Charge SoC at 4.1V for BQ27621-G1 Fuel Gauge

Tarek Sharbo
Prodigy 80 points

Part Number: BQ27621-G1
Other Parts Discussed in Thread: BQSTUDIO

Tool/software:

Dear TI Support Team,

I am currently using the BQ27621-G1 fuel gauge IC in my product for a single-cell 18650 Li-ion battery (nominal 3.7V, full charge 4.2V). The ChemID is left at its default value 0x1202, which is recommended for the cell type I use.

However, I need to configure the gauge such that a battery voltage of 4.1V is interpreted as 100% State of Charge (SoC) instead of 4.2V. In my application, the charger terminates at 4.1V, so I want to define the SoC range as 0% at 2.8V and 100% at 4.1V.

I attempted to change the full charge recognition threshold using BQStudio, but even after the battery is fully charged to 4.1V and charging is terminated, the gauge only reports around 94–97% SoC, which is creating inconsistency in my system.

Could you please advise:

  1. Is it possible to redefine the SoC mapping range, so that 4.1V is considered 100% SoC and 2.8V is 0%?

  2. Can this be achieved through BQStudio or via I2C commands (if so, please share guidance or script format)?

  3. Is ChemID 0x1202 still valid for this voltage range, or would a custom ChemID be required for accurate SoC estimation with a 4.1V charge ceiling?

Any direction you can provide for solving this behavior would be highly appreciated.

Best regards,
Tarek

  • 0
    TI__Guru 70416 points

    You can set the 100% reference voltage with State->V at Chg Term while setting Taper Rate to its maximum (lowest possible taper current).

    You can set the 0% reference voltage with State->Terminate Voltage. Set Delta Voltage to 0mV.

  • 0 in reply to Dominik Hartl11
    Prodigy 80 points

    Dear Dominik,

    Thank you for your clear guidance on configuring V at Chg Term, Taper Rate, and Terminate Voltage. It was very helpful.

    I noticed that after a full reset or power loss, the gauge loses these settings. Is there a way to make these parameters persistent across resets, either through BQStudio or I2C commands?

    I’d appreciate any advice on saving these configurations to avoid reprogramming after each power cycle.

  • 0 in reply to Tarek Sharbo
    TI__Guru 70416 points

    No, you can't make these persistent because this gauge doesn't have persistent memory that you can freely program. The driver will have to check the ITPOR bit and if that's set, indicating that there was a reset of the gauge, then the driver must re-program the gauge.