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BQ24074: Charging stopped at 3.8V

HY yang
Expert 1980 points
Part Number: BQ24074

Customers now use bq24074 to produce rechargeable products. The battery charged is 5000mAh. The customer found that some batteries will not be recharged from 3.0V to 3.8V. At this time, the output of CHG (pin9) keeps jumping (output square wave), Iset (pin16) outputs low level, but it can be recharged from 3.8V to 4.3v after power failure. The circuit diagram is as follows, please help to analyze the cause? thank you.

  • 0
    TI__Mastermind 23220 points

    Hi,

    A pulse on the /CHG pin would indicate that the safety timers have expired. The charging reoccuring from 3.8 to 4.3V after a power failure would indicate a resetting of the safety timers and re-enabling charging. 

    There are a few ways to remedy this issue:

    • Disable the safety timers. This can be done by pulling the TMR pin to ground.
    • Configure the timers to compensate for a large capacity battery. By default, the safety timers with a floating TMR pin is set for 6 hours. This can be extended to 8 hours with a 72k resistor on the TMR pin.
    • Increase the charge current. It looks like the fast charge current is set to 890mA. If this is intentional as set by the battery manufacturer, this is fine. The concern is that the charge current is extending the time to charge. Normally, batterys are safely charged at 1xCapacity. As the BQ24074 can charge up to 1.5A when possibly, a 5000mAh battery should be fine charging at higher currents (again, unless otherwise desired). 
      • This would also require sufficient power on the input to have more current to provide to battery and OUT pin loads

    Let me know if there are further questions.

  • 0 in reply to Anthony P Pham
    Expert 1980 points

    The customer is already testing according to your suggestion.

    There is another question: does bq24074 require anything about the battery?

    What kind of batteries are required? At present, customers are using Boston cells.

  • 0 in reply to HY yang
    TI__Mastermind 23220 points

    Hi,

    The BQ24074 is designed for batteries with Li-Ion/Li-Polymer cell chemistry.

    Looking at the schematic, I noticed the TS connection. Is there information for the NTC and is there a reason for the 12k resistor (R532)?

  • 0 in reply to Anthony P Pham
    TI__Mastermind 23220 points

    Hi,

    Are there any updates here?