BQ24188_15 Datasheet, PDF (24/52 Pages) Texas Instruments – bq24188 2A, 30V, Host-Controlled Single-Input, Single Cell Switchmode Li-Ion Battery Charger with Power Path Management and USB-OTG Support

bq24188
SLUSC44A – DECEMBER 2014 – REVISED MAY 2015
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Device Functional Modes (continued)
9.4.16 Thermal Regulation and Protection
During the charging process, to prevent overheating in the chip, bq24188 monitors the junction temperature, T_J,
of the die and reduces the input current once T_J reaches the thermal regulation threshold, T_REG. The input
current is reduced to zero when the junction temperature increases about 10°C above T_REG. Once the input
current is reduced to 0, the system current is reduced while the battery supplements the load to supply the
system. When the input current is completely reduced to 0 and T_J > 125°C, this is may cause a thermal
shutdown of the bq24188 if the die temperature rises too high. At any state, if T_J exceeds T_SHTDWN, bq24188
stops charging and disables the buck converter. During thermal shutdown mode, PWM is turned off, all timers
are suspended, and 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. The charge cycle resumes when T_J falls below T_SHTDWN by
approximately 10°C.
9.4.17 Charge Status Outputs (STAT, INT)
The STAT/INT output is used to indicate operation conditions for bq24188. STAT/INT is pulled low during
charging when EN_STAT bit in the control register is set to “1”. When charge is complete or disabled, STAT/INT
is high impedance. When a fault occurs, a 128-µs pulse (interrupt) is sent out to notify the host. The status of
STAT/INT during different operation conditions is summarized in Table 1. STAT/INT drives an LED for visual
indication or can be connected to the logic rail for host communication. The EN_STAT bit in the control register is
used to enable/disable the charge status for STAT/INT. The interrupt pulses are unaffected by EN_STAT and will
always be shown.
Table 1. STAT Terminal Summary
CHARGE STATE
Charge in progress and EN_STAT=1
Other normal conditions
Charge mode faults: Timer faults, sleep mode, VIN over voltage, VIN < UVLO or Sleep
mode, BOVP, thermal shutdown, No Battery and Battery Temperature faults
STAT and INT BEHAVIOR
Low
High-Impedance
128-µs pulse, then High Impedance
9.4.18 Boost Mode Operation
In HOST mode, when the operation mode bit (BOOST_EN) in the control register is set to 1, bq24188 operates
in boost mode and delivers 5V to IN to supply USB OTG devices connected to the USB connector. Boost
operation can start with VBAT between 3.45V to 4.5V, and will maintain boost output until VBAT falls to 3.3V. IN
supplies up to 1A to power these devices. It is not recommended to operate boost mode when the battery
voltage is less than 3.3V. Proper operation is not ensured.
9.4.18.1 Chip Disable Input During Boost Mode (CD)
The bq24188 contains a CD input that is used to disable the IC and place the bq24188 into high-impedance
mode. CD must be low to enter boost mode. Driving CD high during boost mode places the bq24188 into high-z
mode and resets the BOOST_EN bit in the I²C. When CD is high, the buck converter is off, and the battery FET
and BGATE are turned on. CD is internally pulled down to GND with a 100kΩ resistor.
9.4.18.2 PWM Controller in Boost Mode
Similar to charge mode operation, in boost mode the IC switches at 1.5MHz to regulate the voltage at IN to 5V.
The voltage control loop is internally compensated to provide enough phase margin for stable operation with the
full battery voltage range and up to 1A.
In boost mode, the cycle-by-cycle current limit is set to 4A or 2A (depending on the I²C setting) to provide
protection against short circuit conditions. If the cycle-by-cycle current limit is active for 8ms, an overload
condition is detected and the device exits boost mode, and signals an over-current fault. Additionally, discharge
current limit (I_LIM(DISCHG)) is active to protect the battery from overload. Synchronous operation and burst mode
are used to maximize efficiency over the full load range.
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