The bq2405x series of devices are highly integrated Li-ion linear chargers devices targeted at
space-limited portable applications. The devices operate from either a USB port or AC adapter.
The bq2405x has a single power output that charges the battery. A system load can be placed in parallel with the battery as long as the average system load does not keep the battery from charging fully during the 10 hour safety timer. The bq24050/2/5 have an integrated USB detect routine that looks for an USB connection on power-up and initially sets the charge input control to either the programmed ISET level, if an adaptor is detected, or to USB100 mode if an USB port is detected. This aides in a faster charge if the battery is discharged and the USB device transceiver is not powered and an adaptor is connected. The battery is charged in three phases: conditioning, constant current and constant voltage. In all charge phases, an internal control loop monitors the IC junction temperature and reduces the charge current if an internal temperature threshold is exceeded. The charger power stage and charge current sense functions are fully integrated. The charger function has high accuracy current and voltage regulation loops, charge status display, and charge termination. The pre-charge current and termination current threshold are programmed via an external resistor on the bq24050/2/5. The fast charge current value is also programmable via an external resistor.