BQ25890_16 Datasheet, PDF (32/69 Pages) Texas Instruments – Adjustable Voltage USB On-the-Go Boost Mode

bq25890, bq25892
SLUSC86B – MARCH 2015 – REVISED MAY 2016
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For example, if ILIM pin is set with 260-Ω resistor, and the ILIM voltage is 0.4 V, the actual input current 0.615 A
- 0.75 A (based on KILM specified). If ILIM pin is open, the input current is limited to zero since ILIM voltage
floats above 0.8 V. If ILIM pin is short, the input current limit is set by the register.
The ILIM pin function can be disabled by setting EN_ILIM bit to 0. When the pin is disabled, both input current
limit function and monitoring function are not available.
9.2.13 Thermal Regulation and Thermal Shutdown
9.2.13.0.1 Thermal Protection in Buck Mode
The device monitors the internal junction temperature T_J to avoid overheat the chip and limits the IC surface
temperature in buck mode. When the internal junction temperature exceeds the preset thermal regulation limit
(TREG bits), the device lowers down the charge current. The wide thermal regulation range from 60ºC to 120ºC
allows the user to optimize the system thermal performance.
During thermal regulation, the actual charging current is usually below the programmed battery charging current.
Therefore, termination is disabled, the safety timer runs at half the clock rate, and the status register
THERM_STAT bit goes high.
Additionally, the device has thermal shutdown to turn off the converter and BATFET when IC surface
temperature exceeds T_SHUT. The fault register CHRG_FAULT is set to 10 and an INT is asserted to the host. The
BATFET and converter is enabled to recover when IC temperature is below T_{SHUT_HYS}.
9.2.13.0.2 Thermal Protection in Boost Mode
The device monitors the internal junction temperature to provide thermal shutdown during boost mode. When IC
surface temperature exceeds T_SHUT, the boost mode is disabled (converter is turned off) by setting
OTG_CONFIG bit low and BATFET is turned off. When IC surface temperature is below T_{SHUT_HYS}, the BATFET
is enabled automatically to allow system to restore and the host can re-enable OTG_CONFIG bit to recover.
9.2.14 Voltage and Current Monitoring in Buck and Boost Mode
9.2.14.1 Voltage and Current Monitoring in Buck Mode
The device closely monitors the input and system voltage, as well as HSFET current for safe buck and boost
mode operations.
9.2.14.1.1 Input Overvoltage (ACOV)
The input voltage for buck mode operation is V_{VBUS_OP}. If VBUS voltage exceeds V_ACOV, the device stops
switching immediately. During input over voltage (ACOV), the fault register CHRG_FAULT bits sets to 01. An INT
is asserted to the host..
9.2.14.1.2 System Overvoltage Protection (SYSOVP)
The charger device clamps the system voltage during load transient so that the components connect to system
would not be damaged due to high voltage. When SYSOVP is detected, the converter stops immediately to
clamp the overshoot.
9.2.14.2 Voltage and Current Monitoring in Boost Mode
The device closely monitors the VBUS voltage, as well as RBFET and LSFET current to ensure safe boost mode
operation.
9.2.14.2.1 VBUS Overcurrent Protection
The charger device closely monitors the RBFET (Q1), and LSFET (Q3) current to ensure safe boost ode
operation. During overcurrent condition when output current exceed (I_{OTG_OCP}) the device operates in hiccup
mode for protection. While in hiccup mode cycle, the device turns off RBFET for t_{OTG_OCP_OFF} (30 ms typical) and
turns on RBFET for t_{OTG_OCP_ON} (250 µs typical) in an attempt to restart. If the overcurrent condition is removed,
the boost converter returns to normal operation. When overcurrent condition continues to exist, the device
repeats the hiccup cycle until overcurrent condition is removed. When overcurrent condition is detected the fault
register bit BOOST_FAULT is set high to indicate fault in boost operation. An INT is also asserted to the host.
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