The BQ24810 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 switching MOSFETs. In case of a MOSFET short or inductor short circuit, the overcurrent condition is sensed by the comparator, the HSFET or LSFET is turned off for the remainder of the switching cycle, and a counter is incremented. The high-side and low-side MOSFETs each have an independent comparator and counter. After either counter reaches seven, 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. The short circuit counters are reset each time that the power stage is enabled, but once either counter reaches seven, the charger is latched off. 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. The low-side MOSFET Vds monitor circuit is enabled by REG0x37[7], and the threshold is 250 mV measured between the PHASE and GND pins. The high-side MOSFET Vds monitor circuit is enabled by REG0x37[6], and the threshold is 750 mV measured between the ACP and PHASE pins, including both the RAC sense resistor and the HSFET. During hybrid boost and battery only boost functions, the low-side MOSFET short circuit protection threshold is used for cycle-by-cycle current limiting, but the charger does not latch off.

Due to the blanking time of the MOSFET short protection, which blanks out the switching noise from when the MOSFET first turns on, the cycle-by-cycle charge overcurrent protection may detect high current and turn off MOSFET before the MOSFET short protection is triggered. In such a case, the charger's MOSFET short protection may not be activated, so that the counter does not count to seven and then latch off. Instead the charger may continuously keep switching with very narrow duty cycle to limit the cycle-by-cycle current peak value. However, the charger should still be safe and does not cause failure because the duty cycle is limited to a very short time and the MOSFET should still be inside the safety operation area. During a soft start period, it may take a long time instead of just seven switching cycles to detect short circuit due to the same reason of the blanking time.