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BQ51050B: Fast-charge timer does not terminate the charging cycle

Robert Basil
Prodigy 30 points
Part Number: BQ51050B

The fast charge timer is listed as 10 hours but the device will continue charging indefinitely.  
My charge current is 250mA and the termination current is 25mA but the system around the device is drawing 70mA.
Because my running current is 70mA and the termination current is 25mA my device will never go below the termination current.
Should the fast charge timer be stopping the charge cycle no mater what?

  • 0
    TI__Guru 70076 points

    Hi Robert

    The 10 hour timer should stop charging and send EPT06 to transmitter which will set a fault condition.

    Couple of things to check:

    1.) If the temp measured by the TS pin is outside the temp range it will suspend charge.

    2.) If the TX / RX glitches and stops power transfer it will restart and the timer will restart.

    Do you have any test logs on charge cycle greater than 10 hours?

  • 0 in reply to Bill Johns
    Prodigy 30 points

    Hi Bill,


    Thanks for the quick reply.

    1- the temp is always OK and the charge never stops.  I am measuring the charge current from the charger back into the system.
    2- I am not sure how to monitor this one.  The charger IC in the charging cradle is a P9242 (Renesas)
    And I do not have any charge logs but I will investigate a way to do so.

    Bottom line though is that no matter how low the charge current or termination current, the timer should expire in 10 hours and stop charging unless some other outside source is happening. Correct?

    A follow-on question if allowed...

    If the timer were to go off and send the EPT, should / could the charge cycle restart if the system were OK (meaning temperature was fine, ect..).
    That could explain why we see it continue forever.

    Best

    Rob

  • 0 in reply to Robert Basil
    TI__Guru 70076 points

    Hi Rob

    Robert Basil said:
    Bottom line though is that no matter how low the charge current or termination current, the timer should expire in 10 hours and stop charging unless some other outside source is happening. Correct?

    Yes, 10 hr should set fault.

    Robert Basil said:
    If the timer were to go off and send the EPT, should / could the charge cycle restart

    It should not restart charge. 

  • 0 in reply to Bill Johns
    Prodigy 30 points

    Hi Bill,

    Since my charge cycle is so slow and the device appears to be charging successfully (except for terminating), could the BQ51050B have exited fast charge mode and entered tamper mode to the timer is no longer active?
    Or does the fast charge timer start during fast charge and never turn off until the charge cycle has successfully completed?

    Best

    Rob

  • 0 in reply to Robert Basil
    TI__Guru 70076 points

    Hi Rob

    Robert Basil said:
    Since my charge cycle is so slow and the device appears to be charging successfully (except for terminating), could the BQ51050B have exited fast charge mode and entered tamper mode to the timer is no longer active?

    The Fast Charge (CC) and Taper Mode (CV) will both be part of the 10 hr timer.

    Robert Basil said:
    Or does the fast charge timer start during fast charge and never turn off until the charge cycle has successfully completed?

    Yes, fast charge will start the timer and termination will complete the charge cycle.