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BQ24172: battery indication led

asher sela
Prodigy 90 points
Part Number: BQ24172

hi

i notice  that when  the charger finished charge a battery to the max voltage that i designed(12v)

when i turn off and turn on    the system

it takes few minutes to the charger "feel" that the battery is full and the charger

keeps charging  untill it finished allthoug the battery isfull .

what is the reason that couses the charger to think that the battery not charged

any idea?

thank you

  • 0
    TI__Expert 8690 points

    Asher,

    What is the voltage of the battery when it initially finishes charging? How much is the fast charge current setting (termination is 10% of this)?

    I'm thinking that the IR drop between the charger and the battery cell at termination is too much. When the charging finishes, the battery cell voltage is still above the recharge threshold, but below the termination current threshold. When you turn off-turn on the system, you reinitialize the charge cycle, so it will detect it still needs to charge more until reaching the termination current.

    Regards,
    Steven

  • 0 in reply to Steven Bangdiwala
    Prodigy 90 points

    hi steven

    as i wrote the voltage that the charger stop the charging is 12v.my fastest charging current is 1 amp.

    the charger stops at 12v.

    i noticed that when the charging led indication led turns off the current is  10% of the fast charging (1A)

    MY Q  IS -  IS THE CHARGING CURRENT IS THE ONLY CONDITION FOR STOPING TO  CHARG THE BATTERY?

      OR THE VOLTAGE   OF THE BATTERY(AS IT SEEN AT FB PIN)  & THE CHARGING CURRENT HAS TO BE AT THE

    "RIGHT" LIMITS IN ORDER TO STOP THE CHARGING?

    THE LENTH BETWEEN THE BATTERY & THE CHARGER IS 22cm./ 22#

    DOES THIS LENTH INFLUNCE THE BEHAVER OF THE CHARGER?

    THANK YOU

  • 0 in reply to asher sela
    TI__Expert 8690 points
    Asher,

    The only condition to stop charging is the charging current reaching the termination current threshold. There are also other conditions as faults, such as the ones mentioned in section 9.3.9. For a normal charge cycle, the only condition would be the termination current.

    The battery may have discharged a bit between the plug off and plug in. Also, the constant voltage region of the charging cycle takes longer to finish. To restart a charge cycle, the battery voltage has to go below VRECHG, but this is not the case if you replug in the adapter, because it will basically start a new charge cycle at adapter plug in. When you replugin, if the charging current is not lower than termination current, then it will take some time until the charging current reaches the termination current.

    You should try to minimize the length between the battery and the charger to charge faster. The less IR drop between them, the better.

    Regards,
    Steven