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BQ24400: BQ24400 can not re-charge the battery

user6544449
Intellectual 795 points
Part Number: BQ24400
Other Parts Discussed in Thread: BQ24105, BQ25172

Dear TI Team,

The attached is our schematic diagram and power distribution diagram. Problems encountered: The adapter is plugged into the instrument, and after the instrument is fully charged, it is discharged until the instrument automatically shuts down, and the automatic shutdown voltage of the instrument is set to 5.1V.
The instrument is used outdoors for a long time. The battery is 5 NiMH batteries connected in series.
I want to know:
1, Adapter was always pluged, why can't the instrument be charged again? What is the main reason for this?
2, Adapter was always pluged, if we want the instrument to automatically charge, can you give a few solutions? (Don't revise the PCB layout). 

Thanks!

  • 0
    TI__Guru**** 165786 points

    Hi,

    What the voltages at BQ24400 pins 4 and 5?

    Regards,

    Jeff

  • 0 in reply to Jeff F
    Intellectual 795 points

    Hello Jeff,

    The pin4 is the voltage form battery voltage(180kΩ+66.5kΩ), the pin5 is connected NTC to GND, 1.9V normally.

  • 0 in reply to user6544449
    TI__Guru**** 165786 points

    Hi,

    I'm sorry. I was not clear.  What are the voltages when the IC is charging correctly and then not charging?  

    Regards,

    Jeff

  • 0 in reply to Jeff F
    Prodigy 110 points

    Hello Jeff,

    The issue is that the instrument will be powered off automaticall before the battery voltage falls to the cutoff voltage. the reason is that not triggered the recharging, and result in the battery voltage is less than 5.1V( the instrument was powered off）. I want to know why instrument is not recharging. and I am appreciated that you give some soltuions for this. I am available for Microsoft Teams, and email is my count.

    Thanks

    Webber

  • 0 in reply to Jiang Webber
    TI__Guru**** 165786 points

    Hi Jiang,

    I need to know the voltages at the IC pins 4 and 5.  You have additional circuitry that I do not understand (as shown below) connected to those pins.  I suspect one of those is not working correctly and causing the charger not to recharge.

    Regards,

    Jeff

  • 0 in reply to Jeff F
    Prodigy 110 points

    Hello Jeff,

    The voltage for Pin4 is more than 1V at the condition of Vbat=5.1V, that can be calculated by =VBAT*(180K+66.5K)/(1M+180K+66.5K). and the voltage for Pin5 is about 1.9V that tested by multimeter.

    Hopes it can help you!

    BRs

    Webber

  • 0 in reply to Jiang Webber
    Prodigy 110 points

    Actually, the voltage for Pin5 is not very high, because the instrument discharge at the current of less than 70mA in the room temperature.  The battery voltage drops and drops to the cutoff voltage(5.1V) for instrument ,during the discharge process, the instument did not start recharge. If start recharge before cutoff voltage for instrument, that is the function that I want. the instrument can be work all the times if adapter was plugged to

  • 0 in reply to Jiang Webber
    TI__Guru**** 165786 points

    Hi Webber,

    Ok.  Those voltages seem okay.  Now I need MOD pin, RC pin and LED voltages:

    Regards,

    Jeff

  • 0 in reply to Jeff F
    Prodigy 110 points

    the LED is not lighting, so I think that the voltage for LED is high. Next Monday, I will test. However,based on state digram for BQ24400, I found that if Adapter is always plugged to, never trigger the VCC reset and battery replacement. So I think that BQ24400 can not start recharge if adapter is plugged to. Am I right?

  • 0 in reply to Jiang Webber
    TI__Guru**** 165786 points

    HI Webber,

    That is also how I read the state diagram.  If you remove and replace VCC or pull BAT pin below 950mV, does the charger start charging? 

    Regards,

    Jeff

  • 0 in reply to Jeff F
    Prodigy 110 points

    Hello Jeff,

    If remove  and replace Vcc(In other words, remove adapter and replug), the charger can start charging. I did the test.

    However, if pull BAT pin below 950mV,  I didn't do the test and I do not know whether the charger start charging.

  • 0 in reply to Jiang Webber
    Prodigy 110 points

    Hello Jeff,

    I rembered that I have the picture about curve of voltage that collected by Data Acquistion(Brand:Agilent) every 3minutes, the minmum of voltage is 5.319V. From the curve, we can get that charge full battery fistly, and than discharge. During discharge process, the BQ24400 can't start charging. Hope that can help you to analyse.

  • 0 in reply to Jiang Webber
    TI__Guru**** 165786 points

    HI Webber,

    From the datasheet:

    The bq24400 initiates a charge cycle when it detects

    • Application of power to VCC

    • Battery replacement

    • Exit from sleep mode

    It does not automatically recharge when the battery voltage droops like our newer chargers.  You may need to add a comparator and a latch that detects when charge is complete and then indicates when recharge needs to occur. Then you could send a pulse to turn off Q2, which would make the charger think power has been removed.

    Regards,

    Jeff

  • 0 in reply to Jeff F
    Prodigy 110 points

    Hello Jeff,

    Thanks for your email.

    In that regard, that is not the best for us.

    If we change another battey management IC, do you have another solution?

    BRs

    Webber

  • 0 in reply to Jiang Webber
    TI__Guru**** 165786 points

    Hi Webber,

    The only other dedicated NiMH charger we have is BQ25172 linear charger for up to 6 cells.  It would need a dc/dc converter in front to lower its input voltage.  Some customers have used BQ24105 switching charger.  Both use timer termination instead of dV/dt or dT/dt termination so it is recommend to charge no higher than 0.5C.

    Regards,

    Jeff

  • 0 in reply to Jeff F
    Prodigy 110 points

    Hello Jeff，

    Thanks for your recommendation.

    Thank you very much

    BRs

    Webber