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Original question:

BQ24780S: Absolute maximum raiting of PHASE

BQ24780S: Operation when the battery is shorted.

user5242682
Prodigy 50 points
Part Number: BQ24780S

Hello experts.

We are evaluating battery shorts.
If the battery is short-circuited without passing the charging current with the charging voltage and charging current set, both register settings will be 0. Is this working as specified?
Thanks and best regards.
Keisuke Iwasaki
  • 0
    TI__Mastermind 33335 points

    When battery voltage on SRN falls below 2.5 V, the converter resets for 1 ms and resumes charge if all the
    enable conditions in the Enable and Disable Charging section are satisfied. This prevents overshoot current in
    the inductor, which can saturate the inductor and may damage the MOSFET. The charge current is limited to 0.5
    A on 10-mΩ current sensing resistor when BATLOWV condition persists and LSFET keeps off. The LSFET turns
    on only for a refreshing pulse to charge BTST capacitor.

    It is normal that charging is stopped when short-circuit is detected. 

  • 0 in reply to Tiger Zhou
    Prodigy 50 points

    Thank you for your reply.

    Please check the following additionally.

    As you mentioned that the load is reduced, the battery is charged again when the short circuit is released.

    When the charging current register was set and there was no load, the charging voltage and charging current were reset to 0mV and 0mA, and charging did not resume even if the short-circuit state was released.

    I think this is different from the battery short operation on the data sheet. Is this the behavior?
    Best regards.
    Keisuke Iwasaki
  • 0 in reply to user5242682
    TI__Mastermind 33335 points

    The bq24780S device has a unique short circuit protection feature. Its cycle-by-cycle current monitoring feature is achieved through monitoring the voltage drop across RDS(on) of the MOSFETs after a certain amount of blanking time. In case of a MOSFET short or inductor short circuit, the overcurrent condition is sensed by two comparators and two counters are triggered. After seven short circuit events, the charger is latched off and ACFET and RBFET are turned off to disconnect the adapter from the system. BATFET is turned on to connect the battery pack to the system. To reset the charger from latch-off status, the IC VCC pin must be pulled below UVLO or the ACDET pin must be pulled below 0.6 V. This can be achieved by removing the adapter and shutting down the operation system. The low-side MOSFET Vds monitor circuit is enabled by REG0x37[7], and the threshold is 750 mV. The high-side MOSFET Vds monitor circuit is enabled by REG0x37[6], and the threshold is 250 mV. During boost function, the low-side MOSFET short circuit protection threshold is used for cycle-by-cycle
    current limiting, charger does not latch up.

  • 0 in reply to Tiger Zhou
    Prodigy 50 points

    Thank you for your reply.

    I think that the content of the reply was the operation when the inductor was short-circuited or the MOSFET was short-circuited, but in this operation, ACFET and RBFET remained ON.

    What are the factors that cause this behavior?

    Best regards.

    Keisuke Iwasaki

  • 0 in reply to user5242682
    TI__Mastermind 33335 points

    https://e2e.ti.com/support/power-management/f/196/t/962967

    This is expected behavior for safety reasons. See above thread.