The bq24901 Li-Ion charge management devices
are designed specifically for off-line charger
applications. The bq24901 resides on the
secondary-side of the transformer and provides
the control feedback to a variety of primary side
controllers. The bq24901 offers current or voltage
regulation feedback, temperature monitoring,
charge status, and adjustable charge termination,
in a single monolithic device. During
battery-absent or charge-complete conditions,
the bq24901 continuously regulates the
secondary-side voltage, used as VCC supply to
the device.
The bq24901 features a time-limited precon–
ditioning phase to condition deeply discharged
cells. The pre-conditioning phase is achieved by
linear regulation in the secondary side. Following
preconditioning, the bq24901 regulates the
charge current to the value set by the external
current sense resistor. Once the battery reaches
the charge voltage, the voltage regulation loop
takes over and completes the charge cycle. The
accuracy of the voltage regulation is better than
±30mV. Charge is terminated based on minimum
current. The minimum current level is set through
TADJ pin. An internal five-hour charge timer
provides a backup for charge termination.
The bq24901 is designed to reliably detect battery
insertion and removal conditions, including packs
with open protectors. Other standard features
include a recharge feature activated when the
battery voltage falls below the VRCH threshold.