bq51050B
bq51051B
SLUSB42C –JULY 2012–REVISED FEBRUARY 2013
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Battery Charge Profile
The bq5105x charger monitors the battery current at all times and reduces the charge current when the system
load requires current above the input current limit. The charge profile is shown in Figure 18.
Precharge
Phase
Current Regulation
Phase
Voltage Regulation
Phase
VRECT-REG
-
Regulation
voltage
IBULK
Rectifier voltage
VBAT + 300mV
VLOWV
(3.0V)
Battery
Voltage
VBAT-SHORT
(1.0V)
35% of IBULK
Charge Current
Termination
Current
Threshold
IPRECHARGE
IBATSHORT
Tx Turned
OFF
Exits
VRECT -TRACK
20% Precharge to
Close Pack Protector
VRECT -TRACK
Figure 18. Li-Ion Battery Charger Profile
This allows for proper charge termination and timer operation. Under normal battery charging conditions, the
system voltage is approximately equal to the battery voltage, however if the battery is deeply discharged, the
system voltage does not drop below 3.5V. This minimum system voltage support enables the system to run with
a defective or absent battery pack and enables instant system turn-on even with a totally discharged battery or
no battery.
The battery is charged in three phases: precharge, fast-charge 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. Additionally, a voltage-based battery pack thermistor monitoring
input (TS) is included that monitors battery temperature for safe charging. The TS function for bq5105x is JEITA
compatible.
Battery Charging Process
Precharge Mode (VBAT ≤ VLOWV
)
The bq5105X enters pre-charge mode when VBAT ≤ VLOWV. Upon entering precharge mode, battery charge
current limit is set to IPRECHARGE. During pre-charge mode, the charge current is regulated to 20% of the fast
charge current (IBULK) setting.
If the battery is deeply discharged or shorted (VBAT < VBAT-SHORT), the bq5105X applies IBAT-SHORT current to bring
the battery voltage up to acceptable charging levels. Once the battery rises above VBAT-SHORT, the charge current
is regulated to IPRECHARGE.
Under normal conditions, the time spent in this pre-charge region is a very short percentage of the total charging
time and this does not affect the overall charging efficiency for very long.
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