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BQ25756: BMS for LiFePo4 2S3P cells configuration.

Tal Cohen
Prodigy 50 points
Part Number: BQ25756
Other Parts Discussed in Thread: , TPS25751, BQ76905

Tool/software:

Hello,

I am looking to build a battery management circuit using Lifepo4 2S3P INR26700 cells topology.

With a nominal battery voltage of 3.2V and 4.5Ah, these cells should give me approx. 86.4Wh and working with 6.4V it is exactly what I need for my application.

The charging voltage is a 7.3V max and 6.75A max for current. I would like to use a USB Type-C PD interface.

Can you please recommend an IC(s) and a BMS charging circuit? (ie. USB controller, charge controller, protection)

Thanks,

-Tal

  • 0
    TI__Mastermind 30615 points

    Hello Tal,

    Thanks for being patient with the wait. Monday was a US holiday.

    I think the BQ25756E might work for your application. What's the input voltage and will your application need to do reverse/source mode?

    For the USB controller, I think the TPS25751 will work. The TPS25751 EVM User's Guide no connecting the BQ25756 and TPS25751 EVMs together.

    Best Regards,
    Ethan Galloway

  • 0 in reply to Ethan Galloway
    Prodigy 50 points

    Thank you, Ethan. my application does not need to use the reverse mode. The charging voltage for this pack should be 7.3V max.

    Can you be more specific on how to connect everything in a 2S3P configuration?

    Thanks,

    -Tal

  • 0 in reply to Tal Cohen
    TI__Mastermind 30615 points

    Hello Tal,

    I think the BQ25756E would be the best fit for this device. At a high level, the USB controller would communicate with the charger over I2C. The I2C commands would program the BQ25756 for the right power contract for the USB cable. The battery monitor would provide the protection and cell balancing for the battery pack. Let me know if you have any questions about this.

    Let me loop in the battery monitor experts to recommend the protection circuitry.

    Best Regards,
    Ethan Galloway

  • 0 in reply to Tal Cohen
    TI__Mastermind 42060 points

    Hello Tal,

    You could use the BQ76905 Battery monitor and protector to provide protections in your BMS! This device can be configured as a 2s device and can provide temperature, current, and cell voltage protections, as well as cell balancing or digitized voltage/current measurements.

    Best Regards,

    Luis Hernandez Salomon

  • 0 in reply to Luis H. S.
    Prodigy 50 points

    To get it all summarised here. I need the TPS25751 I2C connected with the BQ25756 charger. These will be connected to the BQ76905 battery pack protection (mounted on a different board with the batteries). Then everything will be configured using the onboard MPU or the Battery Management Studio tool. Did I get it right?

    Once I have a schematic would it be ok to post it for review?

    Thanks,

    -Tal

  • 0 in reply to Tal Cohen
    TI__Mastermind 42060 points

    Hello Tal,

    You would require an on-board MCU to configure the bq76905 on wake-up. As it cannot be OTP’d with settings.

    Best Regards, 
    Luis Hernandez Salomon