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BQ25895M: Fuel Gauge with Impedance Track™︎ for 800 mAh Battery + Integration with BQ25895M or Alternatives

Martin Tessier
Prodigy 130 points
Part Number: BQ25895M
Other Parts Discussed in Thread: BQ25895, BQ27Z746, BQ27Z561-R2, BQ27411-G1

Tool/software:

Hello,

I'm currently using the BQ25895M battery charger IC in a design powered by a single-cell 800 mAh Li-ion battery. I’m looking to enhance the system by adding battery fuel gauging based on TI’s patented Impedance TrackTm algorithm, with the goal of achieving accurate state-of-charge (SoC) and time-to-empty predictions.

My primary objective is to implement a battery discharge model under real operating conditions to support accurate runtime estimation, improve power management, and enhance the user experience.

I would appreciate your guidance on the following:

  • Which TI Fuel Gauge ICs using Impedance TrackTm would best pair with the BQ25895M for a battery of this capacity (~800 mAh)?

  • Are there alternative single-cell, controlled fast charger ICs with MaxChargeTm or similar functionality, that allow the system to run on a 5V power input (PIM/VBUS) and are known to integrate well with Impedance TrackTm-based fuel gauges?

Thank you for your support and for any design resources or reference materials you can share.

Best regards,
Martin

  • 0
    TI__Genius 17855 points

    Hi Martin,

    Let me loop in someone from the Battery Gauge team to help provide support.

    Best Regards,

    Juan Ospina

  • 0
    TI__Prodigy 380 points

    Hi Martin,

    We have 2 battery gauge options that pair best with BQ25895, these are BQ27Z561-R2 and BQ27Z746. These are both very similar 1S battery fuel gauges with the only difference being the BQ27Z746 has integrated HW and FW protection to drive the protection FETs for higher itnegration.

    Thanks,

    Kipp

  • 0 in reply to Kipp Hayes
    Prodigy 130 points

    Hi Kipp,

    Thank you for the suggestions.

    Could you kindly share a schematic or reference design illustrating how to integrate the BQ25895 with the BQ27Z746 in a typical application? It would be helpful to understand the recommended connections between the two, especially regarding I2C communication, sense lines, and any required supporting components.

    Best regards,
    Martin Tessier

  • 0 in reply to Martin Tessier
    TI__Prodigy 380 points

    Hi Martin,

    BQ27Z746 is a standalone part that has no direct connection to any battery charger. The only way they interact is the TS for temperature and the I2C lines. Both the gauge and charger can be on the same I2C bus with separate I2C addresses. The thermistor will input into the gauge TS pin, then the MCU host can read the temperature from the gauge and write it to the battery charger. This architecture is required as the battery gauge does not allow temperature to be written to it.

    Can see our BQ27Z746 EVM and application schematic as example https://www.ti.com/tool/BQ27Z746EVM-047

    Thanks,

    Kipp

  • 0 in reply to Kipp Hayes
    Prodigy 130 points

    Hi Kipp,

    Thanks again for the detailed explanation.

    After reviewing both options, I think I'll go with the BQ27Z561-R2, which seems more adapted to my application. I’ve also looked through the EVM schematic — one question: do I really need the external protector IC, or can it be omitted in a low-risk, tightly controlled environment?

    Also, do you have any recommendations for a non-BGA (QFN or similar) battery fuel gauge with similar features? I'm trying to simplify assembly where possible.

    Appreciate your insights.

    Best regards,
    Martin

  • +1 in reply to Martin Tessier
    TI__Prodigy 380 points

    Hi Martin,

    The recommendation would be the BQ27411-G1 in QFN package.

    The protector IC is not required but always recommended, especially to help achieve any system safety certifications

    Thanks,

    Kipp