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BQ24616: Behavior when battery pack removed

Ryan.Bishop
Expert 3900 points
Part Number: BQ24616

Hello,

I have two questions on how this charger will behave when a battery pack is removed from the charging bay:

  1. When the battery pack is removed, along with the NTC resistor on the pack, the TS pin on the IC is now biased to an irregular voltage by the fixed resistor divider. With different chargers in the past, we have had problems where the battery charger still thinks there is a battery present and starts a charge timer. We want to ensure this does not happen.
  2. When a battery pack is removed during a charging cycle, do the cycle reset? Meaning if a charge cycle has reached a constant voltage state, but then the pack is removed and a very depleted battery is inserted next, does the charger reset and start from a pre-charge phase? Or would it try to continue from where is left off in constant voltage?

Thank you,
Ryan B.

  • 0
    TI__Guru**** 166626 points
    Hi Ryan,

    Regarding 1, if you remove a fully charged battery and the charger has terminated, then the fast charge safety timer is reset. I need to confirm with design what happens to the timer if you remove a battery before termination and cause the TS fault.

    Regarding 2, ignoring the timer mentioned above, the charger provides the designed pre-charge or fast charge current depending on the voltage level it senses at VFB. If you swamp out a partially or fully charged battery for a depleted battery, the charger's VFB pin senses the low battery voltage and the charger only provides pre-charge current until the battery voltage reaches the precharge to fast charge threshold and then increase to fast charge current. Then when the VFB pin senses that the battery voltage is at the CV voltage, the CV loop prevents the charge from providing more current, thereby keeping the battery voltage at the CV point.
  • 0 in reply to Jeff F
    TI__Expert 6715 points

    Hi Jeff,

    Thank you for this feedback - please let me know what the design team comes back with on #1.

    Regards,
    ~John

  • 0 in reply to John Fedak
    TI__Guru**** 166626 points

    John,

    I checked with the design team and they confirmed that if the TS fault occurs first (most likely) when a partially charged battery is removed, the timer is only suspended, not reset.  So, if another battery is installed, it will start charging and only have the remainder of the safety timer to complete charging.  In this case, we recommend toggling the CE pin to reset the timer. 

  • 0 in reply to Jeff F
    TI__Expert 6715 points
    Hi Jeff,

    A couple follow-up questions:
    1. If the TS Fault doesn't occur (i.e. a partial charged battery is just replaced with a different partially charged battery) will the timers reset?
    a. I believe what we are getting at is the reason the timers don't reset is because it is in a TS Fault first, instead of a battery removal state
    2. Is there a HW solution for resetting the timers (toggling CE) after this combination TS Fault/battery exchange?
    a. The customer doesn't have any MCU/processor on-board to monitor STAT1 and STAT2, and if my understanding is correct - the solution would need to monitor STAT1 to see it go HIGH and then both STAT 1 and STAT2 go LOW (indicating the fault) and then STAT 1 going HIGH again to indicate that the fault has been cleared.

    Regards,
    ~John
  • 0 in reply to John Fedak
    TI__Expert 6715 points
    Hi Jeff,

    Thank you for confirming offline on #1 - that the device will reset the timers if a battery is replaced without the TS Fault going off.

    Regards,
    ~John
  • 0 in reply to John Fedak
    TI__Expert 8130 points

    Hi John,

    1. Yes, the timer will reset. A TS fault would force the IC to suspend the charge timer and omit the battery absent signal.
    2. A possible hardware solution (as discussed offline): Place a logic circuit to control the CE pin based on the voltage at the TS pin. The logic circuit will monitor the voltage on TS pin and check if there's a thermistor or not. Once the TS pin voltage rises above a threshold, it will enable CE. But, be sure that the threshold set is high enough so that a very cold battery will not cause a trip.

    Regards,
    Alejandro