BQ24072 Datasheet, PDF (22/38 Pages) Texas Instruments – 1.2A USB-FRIENDLY Li-Ion BATTERY CHARGER AND POWER-PATH MANAGEMENT IC

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SLUS810A – SEPTEMBER 2008 – REVISED DECEMBER 2008...................................................................................................................................... www.ti.com
PRECHARGE
CC FAST CHARGE
CV TAPER
DONE
V_BAT(REG)
I_O(CHG)
Battery Current
V_LOWV
I_(PRECHG)
I_(TERM)
Battery Voltage
CHG = Hi-z
Figure 39. Typical Charge Cycle
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(LOW) 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.
CHARGE CURRENT TRANSLATOR
When the charger is enabled, internal circuits generate a current proportional to the charge current at the ISET
input. The current out of ISET is 1/400 (±10%) of the charge current. This current, when applied to the external
charge current programming resistor, R_ISET, generates an analog voltage that can be monitored by an external
host to calculate the current sourced from BAT.
V_ISET = I_CHARGE / 400 × R_ISET
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