BQ24187 Datasheet, PDF (14/44 Pages) Texas Instruments – 1A USB-OTG Support

bq24187
SLUSBM0 – APRIL 2014
Not Recommended for New Designs
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8.3 Feature Description
The bq24187 is a highly integrated single cell Li-Ion battery charger targeted for space-limited, portable
applications with high capacity batteries. The single cell charger has a single input that supports operation from
either a USB port or wall adapter supply for a versatile solution. The integrated sense element reduces solution
size and external component count. The charge parameters are programmable using the I2C interface. To
Support USB OTG applications, the bq24187 is configurable to boost the battery voltage to 5V at the input. In
this mode, the bq24187 supplies up to 1A and operates with battery voltages down to 3.3V. The battery is
charged in three phases: precharge, fast charge constant current and constant voltage. In all charge phases, an
internal control loop monitors the IC junction temperature and reduces the charge current if the internal
temperature threshold is exceeded. Additionally, a voltage-based, JEITA compatible battery pack thermistor
monitoring input (TS) is included that monitors battery temperature for safe charging.
The Device Functional Modes section explains these features in detail.
8.4 Device Functional Modes
8.4.1 High Impedance Mode (Hi-Z Mode)
High Impedance mode (Hi-Z mode) is the low quiescent current state for the bq24187. During Hi-Z mode, the
buck converter is off. The bq24187 is in Hi-Z mode when VI_N < V_UVLO, the HZ_MODE bit in the I2C is '1' or the
CD terminal is driven high. Hi-Z mode resets the safety timer.
The bq24187 contains a CD input that is used to disable the IC and place the bq24187 into high-impedance
mode. Drive CD low to enable the bq24187 and enter normal operation. Drive CD high to disable charge and
place the bq24187 into high-impedance mode. CD is internally pulled down to PGND with a 100kΩ resistor.
When exiting Hi-Z mode, charging resumes in approximately 110ms.
8.4.1.1 Input Connected
8.4.1.1.1 Input Voltage Protection In Charge Mode
8.4.1.1.1.1 Sleep Mode
The bq24187 enters the low-power sleep mode if the voltage on VIN falls below sleep-mode entry threshold,
V_BAT+V_SLP, and V_IN is higher than the undervoltage lockout threshold, V_UVLO. This feature prevents draining the
battery during the absence of V_IN. When V_IN < V_BAT+ V_SLP, the bq24187 turns off the PWM converter, sends a
single 128μs pulse is sent on the STAT and INT outputs and the STATx and FAULT_x bits of the status registers
are updated in the I²C. Once V_IN > V_BAT+ V_SLP, the STATx and FAULT_x bits are cleared and the device initiates
a new charge cycle. The FAULT_x bits are not cleared until they are read in the I²C and the sleep condition no
longer exists.
8.4.1.1.1.2 Input Voltage Based DPM (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. Once the supply drops to V_{IN_DPM} (default 4.2V), the charge
current limit is reduced down to prevent the further drop of the supply. When the IC enters this mode, the charge
current is lower than the set value and the DPM_STATUS bit is set. This feature ensures IC compatibility with
adapters with different current capabilities without a hardware change. Figure 7 shows the VIN-DPM behavior to
a current limited source. In this figure the input source has a 750mA current limit and the device charge current is
increased until the input current limit of the adapter is reached and the supply collapses. If the 2X timer is set, the
safety timer is extended while V_IN-DPM is active. Additionally, termination is disabled.
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