Datasheet

bq24072T
bq24075T, bq24079T
SLUS937A –DECEMBER 2009–REVISED APRIL 2010 www.ti.com
INPUT SOURCE NOT CONNECTED
When no source is connected to the IN input, OUT is powered strictly from the battery. During this mode the
current into OUT is not regulated, similar to Battery Supplement Mode, however the short circuit circuitry is
active. If the OUT voltage falls below the BAT voltage by 250mV for longer than t
DGL(SC2)
, OUT is turned off. The
short circuit recovery timer then starts counting. After t
REC(SC2)
, OUT turns on and attempts to restart. If the short
circuit remains, OUT is turned off and the counter restarts. This ON/OFF cycle continues until the overload
condition is removed.
BATTERY CHARGING
Set CE low to initiate battery charging. First, the device checks for a short-circuit on the BAT pin by sourcing
I
BAT(SC)
to the battery and monitoring the voltage. When the BAT voltage exceeds V
BAT(SC)
, the battery charging
continues. The battery is charged in three phases: conditioning pre-charge, constant current fast charge (current
regulation) and a constant voltage tapering (voltage regulation). In all charge phases, an internal control loop
monitors the IC junction temperature and reduces the charge current if an internal temperature threshold is
exceeded.
Figure 32. Typical Charging Cycle
Figure 32 illustrates a normal Li-Ion charge cycle using the bq2407xT. In the pre-charge phase, the battery is
charged at with the pre-charge current (I
PRECHG
). Once the battery voltage crosses the V
LOWV
threshold, the
battery is charged with the fast-charge current (I
CHG
). As the battery voltage reaches V
BAT(REG)
, the battery is held
at a constant voltage of V
BAT(REG)
and the charge current tapers off as the battery approaches full charge. When
the battery current reaches I
TERM
, the CHG pin indicates charging done by going high-impedance.
Note that termination detection is disabled whenever the charge rate is reduced because of the actions of the
thermal loop, the DPPM loop or the V
IN-DPM
loop.
The value of the fast-charge current is set by the resistor connected from the ISET pin to VSS, and is given by
the equation
I
CHG
= K
ISET
/ R
ISET
The charge current limit is adjustable up to 1.5A. The valid resistor range is 590Ω to 3 kΩ. Note that if I
CHG
is
programmed as greater than the input current limit, the battery will not charge at the rate of I
CHG
, but at the
slower rate of I
IN(MAX)
(minus the load current on the OUT pin, if any). In this case, the charger timers will be
proportionately slowed down.
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