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BQ24620: BQ24620 Safety Timer Functions

Alex K16
Intellectual 290 points
Part Number: BQ24620

Hi,

I have a custom charger board utilizing four BQ24620 circuits. They are charging 12.8V, 93Wh packs very slowly. The maximum current is set at 1.22A, which takes about 6 hours to complete.

At about 5-hour mark all four chargers disengage from batteries and then resume charging 15-200 seconds later (see attached graph).

Since the packs are about 80% charged at the 5-hour mark, is there danger of the IC deciding that this is close enough and not resuming charging to add the last 20%?

Thanks,

Alex

  • 0
    TI__Mastermind 24075 points

    Hi Alex,

      The 5 hour mark is due to the inbuilt safety timer, which when tripped will indicate a fault condition and disable charge. If you were to toggle CE or have a POR event, then a new charge cycle will be initiated which would reset the safety timer and charging would resume like normal.

  • 0 in reply to Kedar Manishankar
    Intellectual 290 points

    Hi Kedar,

    Unfortunately there is nothing in our design that would automatically trigger CE or PWR, so we are stuck with waiting until the voltage drops below the recharge voltage, error clears and the charging resumes.

    My question is this: which one of the following statements is true:

    A -  It is ok to let the timeout error occur. There is nothing wrong with waiting for a minute or two for the charging to resume even if the error occurs at the 80% charge point.

    B - It is not advisable to allow the timeout to occur so close to the maximum charge point as this can have unintended consequences.

    What do you think?

    Thanks,

    Alex

  • 0 in reply to Alex K16
    TI__Mastermind 24075 points

    Hi Alex,

        A. There is no issue with not fully charging from the charger's standpoint. When charge cycle resumes the charger will resume charging like normal as duty cycle will just be based off of what battery voltage (VFB) is sensed by the charger. The only unintended consequence would be if the battery is required to supply a load, as not fully charging the battery will reduce the run-time of the battery as it is not fully charged.