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BQ24250: BQ24250 - Capabilities and Register Configuration Retention

Wayne Olsen
Prodigy 10 points
Part Number: BQ24250
Other Parts Discussed in Thread: BQ25892

Hello,

I am working implementing the BQ24250 but I have a few questions that I have not been able to find in past posts or through the datasheet.

1) Would there be a concern regarding cell capacity with this charger (besides temperature as noted in the datasheet)?  The project will be a re-use type idea that will have a single cell with an anticipated capacity of 10Ah.  From conversations, it sounds like that they cells are a 1S3P configuration, and may be challenging to separate a single cell out.  This would mean a potential 30Ah capacity, are there concerns with using this for such a large capacity?  The project is meant to be low current applications (2Amps in or out).

I have read about the self-timeout of 6hours default, so I do understand that this would need to be disabled to achieve the required duration to fully charge.

2) The cells are second use so their Regulated Voltage is target at 4.1V.  This would require adjusting Register #3 VBATREG.  The problem is I cannot understand how I would appropriately configure that register to achieve a 4.1V regulated voltage.  I would assume that setting any of the VBATREG registers TRUE would indicate an offset to the 4.44 maximum VBATREG.  Based on what is defaulted in the registers (640mV/40mV/20mV = 720mV offset), and the default Regulated Voltage of 4.2V, I do not understand how to set this register to achieve 4.1V.  What would be the proper way to configure?

3) Since I will be using the I2C for configuration (I do not plan to use the Watchdog), are the registers retained across Loss of Power to the BQ24250 (Volatile vs. non-volatile)?  Or would they need to be configured if power is lost?

Thank you for the support on these questions!

Wayne

  • 0
    TI__Expert 8230 points

    Hello Wayne,

    30Ah battery pack should work fine, but with a 2A charge current it wil take a long time to charge. A rough estimate of charge time is charge capacity/charge current * 1.3; this means a 30Ah pack will take approximately 19.5 hours to charge. The safety timer on the bq24250 can only reach 9 hours, so like you mentioned, it would need to be disabled to charge a deeply discharge battery fully. If you want to have a safety timer on your application, we do offer other charger solutions that have safety timers that can go up to 20 hours, such as the bq25892. This charger also can provide higher charge current than 2A if charge time is a concern for your application. I recommend doing a full charge cycle on the 30Ah pack and verify the exact charge time to determine if 20 hours would fit your application.

    For a charge regulation voltage of 4.1V, you would need to modify REG02[7:2] = 011110b via I2C.

    Regarding the register retention, the I2C registers will maintain their contents as long as the battery voltage is higher than the battery UVLO threshold (minimum of 2.3V) or VBUS is less than the VBUS UVLO threshold (minimum 3.6V). This means if your battery is connected with a voltage higher than 2.3V, the I2C registers will retain their values even if the VBUS is disconnected. If the battery ever gets deeply discharged or the protectors on the battery pack open without adapter present, the registers will need to be reprogrammed by the host via I2C upon startup. If you have a fuel gauge on your system, you can use this to determine when to perform an orderly shutdown of your system when the battery voltage is reaching 2.3V.

    Let me know if you have any other questions.