BQ24165_14 Datasheet, PDF (15/38 Pages) Texas Instruments – 2.5A, Dual-Input, Single Cell Switch Mode Li-Ion Battery Charger with Power Path Management

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SLUSAP4B – DECEMBER 2011 – REVISED MARCH 2013
BATTERY CHARGING PROCESS
Assuming a valid input source has already been attached to IN or USB, as soon as a deeply discharged or
shorted battery is attached to the BAT pin, the bq24165/6/7 applies a 50mA current to bring the battery voltage
up to acceptable charging levels. During this pre-charge time, the battery FET is linearly regulated to maintain
the system output regulation at V_SYS(REG). Once the battery rises above V_BATSHRT, the charge current increases to
the fastcharge current setting. The SYS voltage is regulated to V_SYS(REG) while the battery is linearly charged
through the battery FET. Under normal conditions, the time spent in this region is a very short percentage of the
total charging time, so if the charge current is reduced, the reduced charge rate does not have a major negative
effect on total charge time. If the current limit for the SYS output is reached (limited by the input current limit, or
V_IN-DPM), the charge current is reduced to provide the system with all the current that is needed. If the charge
current is reduced to 0mA, pulling further current from SYS causes the output to fall to the battery voltage and
enter supplement mode (see the Dynamic Power Path Management section for more details).
Once the battery is charged enough to where the system voltage begins to rise above V_SYSREG (depends on the
charge current setting), the battery FET is turned on fully and the battery is charged with the charge current
programmed using the ISET input, I_CHARGE. The slew rate for fast charge current is controlled to minimize the
current and voltage over-shoot during transient. The charge current is programmed by connecting a resistor from
ISET to GND. The value for R_ISET is calculated using Equation 1:
R_{ISE T} = ^{K IS ET}
I_CHARGE
(1)
Where I_CHARGE is the programmed fast charge current and K_ISET is the programming factor found in the Electrical
Characteristics table.
The charger's constant current (CC) loop regulates the charge current to I_CHARGE until the battery reaches close
to the regulation voltage. Once the battery voltage is close to the regulation voltage, V_BATREG, the charge current
step downs sharply as the constant voltage (CV) loop takes over, the internal battery FET turns on full, tying SYS
to BAT and the charger tapers down the charge current as shown in Figure 1. The voltage regulation feedback
occurs by monitoring the battery-pack voltage between the BAT and PGND pins.
The bq24165/6/7 monitors the charging current during the voltage regulation phase. If the battery voltage is
above the recharge threshold and the charge current has naturally tapered down to and remains below
termination threshold, I_TERM, without disturbance from events like supplement mode for 32ms, the bq24165/6/7
terminates charge and turns off the battery charging FET. If V_SYS > V_MINSYS and the charge current has been
reduced due to V_INDPM,the input current loop or thermal protection circuits or USB100mode, the charger disables
termination. The system output is regulated to the V_BAT(REG) voltage and supports the full current available from
the input. Battery supplement mode (see the Dynamic Power Path Management section for more details) is still
available for SYS load transients. Supplement mode events occurring repeatedly within the 32ms deglitch
window will prevent termination and can cause the charger to exit termination.
Charging resumes when one of the following conditions is detected:
1. The battery voltage falls below the V_BAT(REG)-V_RCH threshold
2. V_SUPPLY Power-on reset (POR)
3. CE1 CE2 toggle or CE toggle
4. Toggle Hi-Impedance mode (using IUSB_)
A new charge cycle is initiated only in the event of V_SUPPLY POR or the battery being removed and replaced. If
the battery voltage, V_BAT, is ever greater than V_BATREG (for example, when an almost fully charged battery enters
the JEITA WARM state per the TS pin or CE1 and CE2 are configured to reduce V_BATREG) but less than V_BOVP,
the reverse boost protection circuitry may activate as explained later in this datasheet. If the battery is ever
above V_BOVP, the buck converter turns off and the internal battery FET is turned on. This prevents further
overcharging the battery and allows the battery to discharge to safe operating levels.
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