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BQ24171: Possibility of overcurrent during charge?

Oliver Bailey
Prodigy 30 points
Part Number: BQ24171
Other Parts Discussed in Thread: BQ40Z50

Hi TI,

One of our products is a Lithium-Ion battery charger cradle using the BQ24171. The battery pack to be charged is developed by a 3rd party, using the BQ40Z50 IC with R4 firmware. The battery pack is a 3S1P arrangement of 18650 cells.

A customer had an issue during charge in which the battery pack went to Permanent Fail (PF) mode, indicating an Overcurrent during Charge (OCC2) event, recording 5.5A for 3 seconds during charge, over the programmed limit of 3.2A. 

Our charger base is powered by an AC/DC USB-C adapter, and our charger base negotiates 15V @ 3A from the AC/DC adapter. This 15V / 3A supply is passed to the BQ24171 to charge the battery pack at approximately 2.0A output current, to a maximum 12.4V. Full schematics of charger base and battery pack can be provided by email on request.

My question is: to TI's knowledge, is there any scenario / circumstance in which the BQ24171 IC can provide excessive charging current (i.e. more than expected or set by the ISET resistive divider?

Many thanks,
Oli.

P.S. As part of this question, I am wondering if the output switching inductor (3.3A Bourns SRN80403R3Y in our application) or the 10 milliOhm "R_SR" output sense resistor (Susumu KRL1632E-M-R010-F-T5) could be critical to this possibility? E.g. if the inductor is damaged and has lower than expected inductance or saturation current, or if the sense resistor, when in use has lower than expected resistance due to e.g. moisture or contamination. But particularly, if there is any circumstance in which the BQ24171 itself could be tricked/fooled/misused to allow excessive charging current?


  • 0
    TI__Guru*** 146695 points

    Hi Oliver,

    The charger measures the current across the sense resistor to determine how much charge current to provide.  The ISET resistor is sized based on the size of the sense resistor.  If the sense resistor is partially shorted or the ISET pin resistors change value in the wrong direction, charge current would increase.  I doubt the issue is related to the inductor because even if shorted, the charge has OCP as explained below:

    Regards,

    Jeff