LP3910SQ-AN Datasheet, PDF (38/60 Pages) National Semiconductor (TI) – Power Management IC for Hard Drive Based Portable Media Players

charging, the battery voltage steadily increases while charged
with a constant current (CC). The three charger status bits
STAT2, STAT1 and STAT0 are respectively low, high, and
low. The full-rate charge current is selected using the Charge
Control Register, which defaults to 100 mA.
It is recommended to charge Li-Ion batteries at a rate of 1C,
where “C” is the capacity of the battery. As an example, it is
recommended to charge a battery with a capacity of
800 mAh at 800 mA, or 1C. Charging at a higher rate may
compromise the quality and lifetime of the battery.
Constant-Voltage (CV) Charging Mode
The battery voltage increases rapidly as a result of full-rate
charging and once it reaches the programmable termination
voltage of either 4.1V, 4.2V or 4.38V, the charger will move
to constant-voltage charge mode. During this mode, the
charge current gradually decreases while the battery remains
at the termination voltage. The termination voltage can be
selected to be either 4.1V, 4.2V or 4.38V by programming bits
D6 and D7 in the Charger Control register to accommodate
different battery chemistries. In CV charging mode, the
Charge Control Status bits STAT2, STAT1 and STAT0 are
respectively logic 0, logic 1 and logic 1.
TOP-OFF Charging Mode
When the charge current reduces to the EOC threshold (pro-
grammable to 5% or 10% of programmed full rate charge
current), constant voltage charging will continue for an addi-
tional 21 minute TOP-OFF time period. In TOP-OFF charging
mode, the Charge Control Status bits STAT2, STAT1 and
STAT0 are respectively logic 1, logic 1 and logic 1. At the end
of the TOP-OFF period, the charger transitions to Charge Cy-
cle Complete.
Charge Cycle Complete
During Charge Cycle Complete, the charger is automatically
disabled, regardless of the state of the Charge Enable Bit. In
Charge Cycle Complete, the STAT2, STAT1 and STAT0 bits
are respectively logic 1, logic 0 and logic 1. When the Battery
Voltage drops below the V_RESTART threshold, charging will re-
sume in Full-Rate Charging Mode.
Battery Temperature Monitoring (T_S pin)
The LP3910SQ-AN is equipped with a battery thermistor ter-
minal to continuously monitor the battery temperature by
measuring the voltage between the T_S pin and GND. With the
T_S pin connected to the battery thermistor, charging is allowed
only if the battery temperature is within the acceptable tem-
perature range set by a pair of internal comparators inside the
LP3910SQ-AN. The temperature window is 0°C–45°C or 0°
C–50°C, depending on the setting of D2 of the Charger Su-
pervisory (CHSPV) register. There is 3ºC of temperature
hysteresis associated with each temperature threshold. The
default temperature range is 0°C–50°C and can be changed
to 0°C–45°C by setting bit D3 in the CHSPV register. If the
battery temperature is out of range, STAT2, STAT1 and
STAT0 bits in the CHSPV Register are set to logic1, logic0,
logic0, and charging is suspended.
The T_S pin is only active during charging and draws no current
from the battery when no external power source is present.
If the T_S pin is not used in the application, it should be con-
nected to GND through a 10 kΩ pulldown resistor.
When the T_S pin is left floating (battery removal), then the
charger will be disabled as the T_S voltage exceeds the lower
temperature limit.
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Disabling Charger
Charging can be safely interrupted by clearing the Charge
enable bit D1 in the Charge Control Register and can subse-
quently resume upon setting this bit. When the charger is
disabled, STAT2, STAT1, and STAT0 bits in the CHSPV reg-
ister are set to logic 0.
Safety Timer
In order to prevent endless charging, which could degrade the
battery quality and life time, the LP3910SQ-AN contains a
safety timer that limits charging regardless whether the bat-
tery has reached its full capacity or not. In prequalification the
safety timer is 1 hour. In full rate or constant voltage charging
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