The bq2407xT series of devices are integrated Li-ion linear chargers and system power
path management devices targeted at space-limited portable applications. The devices operate from
either a USB port or AC adapter and support charge currents up to 1.5A. The input voltage range
with input over-voltage protection supports unregulated adapters. The USB input current limit
accuracy and start up sequence allow the bq2407xT to meet USB-IF inrush current specification.
Additionally, the input dynamic power management (VIN - DPM) prevents the
charger from crashing incorrectly configure USB sources.
The bq2407xT features dynamic power path management (DPPM) that powers the system while
simultaneously and independently charging the battery. The DPPM circuit reduces the charge current
when the input current limit causes the system output to fall to the DPPM threshold; thus,
supplying the system load at all times while monitoring the charge current separately. This feature
reduces the number of charge and discharge cycles on the battery, allows for proper charge
termination and enables the system to run with a defective or absent battery pack.
Additionally, the regulated system input enables instant system turn-on when plugged in
even with a totally discharged battery. The power-path management architecture also permits the
battery to supplement the system current requirements when the adapter cannot deliver the peak
system currents, enabling the use of a smaller adapter.
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 the 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
input current limit and charge current are programmable using external resistors.
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