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BQ24070RHLT False Battery Absent Indication

Damon Kutten
Prodigy 90 points

On some units, the BQ24070RHLT charger will begin to toggle between charging and charge done when the AC charger is plugged in, at a rate of about 3Hz. This is normally supposed to indicate that the battery is absent. But in this case the Li Ion battery is present, and operating normally. The charge level of the battery is about 3.9V. The condition appears to persist indefinitely. During this time, the charger supplies only a small amout of current to the battery (70mA, declining slowly to about 6mA), and the battery voltage level appears to remain constant. The expected charge current is 700mA or more. To get out of this condition, the AC charger must be reseated, sometimes more than once. This problem does not happen every charge cycle; some charge cycles complete correctly. Do you have any idea why the device is behaving in this way?

  • 0
    TI__Mastermind 31120 points

    The issue is that the gain of the battery sense circuit becomes larger when the BAT FET is fully on and thus the ISET current is reduced with allows termination at a higher curent level.  This happens with an excessive load (more than the input can supply) as the battery passes the refresh threshold, termination is allowed if the ISET pin falls to 0.25V.  Once terminated, the part will refresh, and start a new charge. 

    One solution is to decrease the load (system and charging) so the OUT voltage does not drop near the battery votlage, or increase the available source current.

      Is your adaptor being pulled into current limit....is PSEL set for an adaptor?

    Another solution is to raise the DPPM threshold above the battery voltage so the part goes into DPPM before the BAT FET get crushed (fully on).