Datasheet

Termination
Regulation
Current
Regulation
voltage
Precharge
Phase
Current Regulation
Phase
Voltage Regulation
Phase
Charge Current
Battery
Voltage
V
SYS
System Voltage
Linear Charge
to Maintain
Minimum
System
Voltage
V
BATSHORT
I
BATSHORT
50mA Linear Charge
to Close Pack
Protector
Battery FET is ON
Battery
FET
is OFF
bq24278
SLUSB04 –JUNE 2012 www.ti.com
DETAILED DESCRIPTION
The bq24278 is a highly integrated single cell Li-Ion battery charger and system power path management
devices targeted for space-limited, portable applications with high capacity batteries. The power path
management feature allows the bq24278 to power the system from a high efficiency DC to DC converter while
simultaneously and independently charging the battery. The charger monitors the battery current at all times and
reduces the charge current when the system load requires current above the input current limit. This allows for
proper charge termination and enables the system to run with a defective or absent battery pack. Additionally,
this enables instant system turn-on even with a totally discharged battery or no 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. This enables 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.
Charge Mode Operation
Charge Profile
Charging is done through the internal battery MOSFET. When the battery voltage is above 3.5V, the system
output (SYS) is connected to the battery to maximize the charging efficiency. There are 5 loops that influence the
charge current; constant current loop (CC), constant voltage loop (CV), thermal regulation loop, minimum system
voltage loop (MINSYS) and input voltage dynamic power management loop (V
IN-DPM
). During the charging
process, all five loops are enabled and the dominant one takes control. The bq24278 supports a precision Li-Ion
or Li-Polymer charging system for single-cell applications. The minimum system output feature regulates the
system voltage to a minimum of V
SYS(REG)
, so that startup is enabled even for a missing or deeply discharged
battery. Figure 2 shows a typical charge profile including the minimum system output voltage feature.
Figure 2. Typical Charging Profile of bq24278
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