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BQ25756: Configuration and Battery Fuel Gauge selection for 8S2P Li-Ion Battery Pack

Rafael Moraes
Prodigy 60 points
Part Number: BQ25756
Other Parts Discussed in Thread: , BQSTUDIO, BQ34Z100, BQ34110

Hi TI,

I am designing a system which requires a Li-ion Battery pack with the following configuration: 8 series / 2 parallel. (3.7V * 8 = 29.6V nominal, 6.7Ah).

This battery pack configuration requires a charging voltage of 4.2V * 8 = 33.6V, and 1A charging current.

I am considering using the BQ25756 as the battery pack charger for this system.

How do I configure the BQ25756EVM for this system?

The AC-DC Power supply which will be the input of the charger will either be 36V or 48V, 6A.

Which of these options is best for this system?

I also need to monitor this battery pack using a Battery Fuel Gauge.

Which Battery Fuel Gauge do you recommend to monitor this battery pack?

The system requires 24V to operate, so with this charger configuration, can I connect the charger VSYS to a 24V buck-regulator to power the system?

(The system power must not interrupt when commuting power supply and battery)

Thanks,

Rafael

  • +1
    TI__Mastermind 31400 points

    Hello Rafael,

    Thanks for working with us. I'm the applications engineer for the BQ25756.

    Rafael Moraes said:

    How do I configure the BQ25756EVM for this system?

    You'll need to adjust R64 to get a charging voltage of 33.6V. You can check the BQ25756 design calculator to get the right resistor values.

    You'll need to set the charging current, ICHG_REG, to 1A. You can do this through BQStudio.

    Rafael Moraes said:

    The AC-DC Power supply which will be the input of the charger will either be 36V or 48V, 6A.

    Which of these options is best for this system?

    I'd recommend the 48V, 6A power supply.

    Rafael Moraes said:

    Which Battery Fuel Gauge do you recommend to monitor this battery pack?

    Let me loop in the experts on fuel gauges for this question.

    Rafael Moraes said:

    The system requires 24V to operate, so with this charger configuration, can I connect the charger VSYS to a 24V buck-regulator to power the system?

    Yes, this should work. What is the load of the System?


    Best Regards,
    Ethan Galloway

  • 0
    TI__Guru 62386 points

    TI gauges that support 8s2p are:

    Impedance Tracking: bq34z100

    CEDV: bq34110

  • 0 in reply to Ethan Galloway
    Prodigy 60 points

    Hi Ethan,

    Thanks for the quick reply.

    The load of the system can go up to 6A including the battery charge, that's why I want to limit the battery charge at 1A.

    I see now that TI also has "Battery Monitors & Balancers" which I couldn't distinguish the application from "Battery Fuel Gauge".

    Can you give a simple compare and contrast between both battery management type of ICs?

    For the 24V 4A regulator, does TI have any recommendation?

     

    Best regards,

    Rafael

  • 0 in reply to Rafael Moraes
    TI__Mastermind 31400 points

    Hello Rafael,

    If your system load is 6A, you might want to consider setting your charge current to 6A. That way, you won't have to worry about your battery draining under full load while you have power applied.

    Best Regards,
    Ethan Galloway

  • 0 in reply to Ethan Galloway
    Prodigy 60 points

    Hi Ethan,

    My system needs to be powered by VSYS and commute to VBAT if the AC is disconnected, but the J2 connector and other components are DNP.

    Which components are required to be installed in the BQ25756EVM to be able to do this?

    Best regards,

    Rafael

  • 0 in reply to Rafael Moraes
    TI__Mastermind 31400 points

    Hello Rafeal,

    The BQ25756 is a non-power path part. The system load needs to be connected to the battery.

    Best Regards,
    Ethan Galloway