BQ24266_15 Datasheet, PDF (16/41 Pages) Texas Instruments – bq24266 3A, 30V Standalone Single-Input, Single-Cell Switchmode Li-Ion Battery Charger

bq24266
SLUSBY5F – JUNE 2014 – REVISED AUGUST 2015
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7.3 Feature Description
The bq24266 is a highly integrated single cell Li-Ion battery charger and system power path management
devices that supports operation from either a USB port or wall adapter supply. The power path feature allows the
bq24266 to power the system from a high efficiency DC to DC converter while simultaneously and independently
charging the battery. The power path also permits the battery to supplement the system current requirements
when the adapter cannot. Many features are programmable using dedicated pins. To support USB OTG
applications, the bq24266 is configurable to boost the battery voltage to 5V and supply up to 1A at the input. The
battery is charged with three phases: precharge, constant current and constant voltage. Thermal regulation
prevents the die temperature from exceeding 125°C. With the bq24266, a JEITA compatible battery pack
thermistor monitoring input (TS) is included to prevent the battery from charging outside of its safe temperature
range.
7.4 Device Functional Modes
7.4.1 High Impedance Mode
High Impedance mode (Hi-Z mode) is the low quiescent current state for the bq24266. During Hi-Z mode, the
buck converter is off, and the battery FET and BGATE are on. SYS is powered by BAT. The bq24266 is in
Hi-Z mode when V_IN < V_UVLO or the IUSB1, IUSB2, and IUSB3 pins are all driven high. Hi-Z mode resets the
safety timer. When exiting Hi-Z mode, charging resumes in approximately 110ms.
7.4.2 Battery Only Connected
When the battery is connected with no input source, the battery FET is turned on. After the battery rises
above V_BATUVLO and the deglitch time, t_DGL(BAT), the SYS output starts to rise. In this mode, the current is not
regulated; however, there is a short circuit current limit. If the short circuit limit (I_LIM(DISCHG)) is reached for the
deglitch time (t_DGL(SC)), the battery FET is turned off for the recovery time (t_REC(SC)). After the recovery time,
the battery FET is turned on to test and see if the short has been removed. If it has not, the FET turns off
and the process repeats until the short is removed. This process protects the internal FET from over
current. If an external FET is used for discharge, the body diode prevents the load on SYS from being
disconnected from the battery and t_DGL(BAT) is not applicable.
7.4.3 Input Connected
7.4.3.1 Input Voltage Protection in Charge Mode
7.4.3.1.1 Sleep Mode
The bq24266 enters the low-power sleep mode if the voltage on V_IN falls below sleep-mode entry threshold,
V_BAT+V_SLP, and V_IN is higher than the undervoltage lockout threshold, V_UVLO. In sleep mode, the input is isolated
from the battery. This feature prevents draining the battery during the absence of V_IN. When V_IN < V_BAT+ V_SLP,
the bq24266 turns off the PWM converter and turns the battery FET and BGATE on. Once V_IN > V_BAT+ V_SLP, the
device initiates a new charge cycle.
7.4.3.1.2 Input Voltage Based Dynamic Power Management (V_IN-DPM)
During normal charging process, if the input power source is not able to support the programmed or default
charging current, the supply voltage deceases. Also, at higher currents, large input line impedances may cause
the voltage at the device to droop. Once the supply drops to V_{IN_DPM} (default 4.2V), the charge current limit is
reduced to prevent the further drop of the supply. When the IC enters this mode, the charge current is lower than
the set value. This feature ensures IC compatibility with adapters with different current capabilities without a
hardware change. Figure 9 shows the V_IN-DPM behavior to a current limited source. In this figure the input
source has a 2A current limit and the device is charging at 1A. A 2.5A load transient then occurs on V_SYS causing
the adapter to hit its current limit and collapse, while V_SYS goes from V_SYSREG(LO) to V_MINSYS. The safety timer is
extended while V_IN-DPM is active. Additionally, termination is disabled.
The V_INDPM threshold for the adapter modes (1.5A and 2.5A) is set using a resistor divider with VDPM connected
to the center tap. Select 10kΩ for the bottom resistor. The top resistor is selected using equation Equation 1.
Where V_{IN_DPM} is the desired V_{IN_DPM} threshold and VDPM is the regulation threshold at the pin specified in the
Electrical Characteristics table.
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