BQ25040 Datasheet, PDF (12/25 Pages) Texas Instruments – 1.1A, Single-Input, Single Cell Li-Ion Battery Charger With 50mA LDO and 2.3A Production Test Support

bq25040
SLUS910B – MARCH 2009 – REVISED MARCH 2009 ...................................................................................................................................................... www.ti.com
DETAILED FUNCTIONAL DESCRIPTION
The bq25040 has a single power output that charges a single cell Li-Ion battery from a USB or AC Adapter
source. A system load can be placed in parallel with the battery. The charge current is programmed using the
ISET and EN/SET inputs. The charge current is programmable to USB100, USB500 or a user programmed
charge current up to 1.1A. A Production Test mode is available that supplies up to 2.3A at 4.2V. Additionally, a
4.9V, 50mA linear regulator (LDO) is integrated into the IC for supplying low power external circuitry. The charger
power stage and charge current sense functions are fully integrated. The charger function has high accuracy
current and voltage regulation loops, charge status display, and charge termination.
Battery Charge Control (BAT)
Charging begins when a battery with a voltage less than V_RCH is installed, a valid input source is connected and
the EN/SET input is low. A valid input source is defined as V_IN greater than V_BAT + 80mV and less than V_OVP.
Additionally, V_IN must be above the UVLO. The battery is charged in three phases: conditioning precharge,
constant current fast charge (current regulation) and 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 21 shows a typical charge profile.
PRECHARGE CC FAST CHARGE
CV TAPER
V_OUT(REG)
I_FASTCHG
Battery
Current
V_LOWV
I_PRECHG
I_CHGDONE
Battery
Voltage
Battery Full
CHG + Hi-Z
Figure 21. Typical Charge Cycle
When the battery is first installed, the device enters precharge mode. While V_BAT is less than V_LOWV, the bq25040
remains in precharge mode where the current limit is set to 20% of the current limit programmed at ISET. Once
V_BAT exceeds V_LOWV, the bq25040 enters fast charge mode where the current limit is set by the EN/SET input
(USB100, USB500, or ISET. See the Input Current Limit section for details). After the battery is charged up to the
V_BAT(REG), the device enters voltage regulation. V_BAT is regulated to V_BAT(REG) as the charge current is reduced.
Once I_BAT decreases to the termination current threshold set by IFULL, the CHG output goes high impedance but
charging continues. Figure 21 graphically illustrates a typical charge cycle. The bq25040 does not contain charge
safety timers, so all safety timers must be done by the host processor.
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