BQ24165 Datasheet, PDF (15/35 Pages) Texas Instruments – 2.5A, Dual-Input, Single Cell Switch Mode Li-Ion Battery Charger with Power Path

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bq24165
bq24166
bq24167
SLUSAP4A – DECEMBER 2011 – REVISED MARCH 2012
BATTERY CHARGING PROCESS
When the battery is deeply discharged or shorted, the bq24165/6/7 applies a 50mA current to bring the battery
voltage up to acceptable charging levels. During this 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 charge current is regulated to I_CHARGE until the battery is charged to the regulation voltage. Once the battery
voltage is close to the regulation voltage, V_BATREG, the charge current is tapered down as shown in Figure 1 while
the SYS output remains connected to the battery. 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. Once the termination
threshold, I_TERM, is detected and the battery voltage is above the recharge threshold, the bq24165/6/7 terminates
charge and turns off the battery charging FET. 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.
A charge cycle is initiated 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 Input toggle or CE toggle
4. Toggle Hi-Impedance mode (using IUSB_)
If the battery voltage is ever greater than V_BAT(REG), the PWM converter is turned off and the battery is discharged
to V_BATREG-V_RCH. Additionally, 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.
DYNAMIC POWER PATH MANAGEMENT
The bq24165/6/7 features a SYS output that powers the external system load connected to the battery. This
output is active whenever a source is connected to IN, USB or BAT. The following sections discuss the behavior
of SYS with a source connected to the supply (IN or USB) or a battery source only.
INPUT SOURCE CONNECTED
When a source is connected to IN or USB, and the bq24165/6/7 is enabled, the buck converter starts up. If
charging is enabled using CE1 and CE2(bq24165) or CE (bq24166/7), the charge cycle is initiated. When V_BAT >
3.5V, the internal battery FET is turned on and the SYS output is connected to V_BAT. If the SYS voltage falls to
V_SYS(REG), it is regulated to that point to maintain the system output even with a deeply discharged or absent
battery. In this mode, the SYS output voltage is regulated by the buck converter and the battery FET is linearly
regulated to regulate the charge current into the battery. The current from the supply is shared between charging
the battery and powering the system load at SYS. The dynamic power path management (DPPM) circuitry of the
bq24165/6/7 monitors the SYS voltage continuously. If V_SYS falls to V_MINSYS, the DPPM circuit adjusts charge
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