BQ24297 Datasheet, PDF (34/48 Pages) Texas Instruments – I2C Controlled 3A Single Cell USB Charger

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bq24297
SLUSBP6A – SEPTEMBER 2013 – REVISED OCTOBER 2013
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Thermal Regulation and Thermal Shutdown
During charge operation, the device monitors the internal junction temperature T_J to avoid overheat the chip and
limits the IC surface temperature. When the internal junction temperature exceeds the preset limit (REG06[1:0]),
the device lowers down the charge current. The wide thermal regulation range from 60°C to 120°C 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 REG08[1]
goes high.
Additionally, the device has thermal shutdown to turn off the converter. The fault register REG09[5:4] is 10 and
an INT is asserted to the host.
Voltage and Current Monitoring in Buck Mode
The device closely monitors the input and system voltage, as well as HSFET and LSFET current for safe buck
mode operation.
Input Over-Voltage (ACOV)
The maximum 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 REG09[5:4] will be set to 01. An
INT is asserted to the host.
System Over-Voltage 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.
Voltage and Current Monitoring in Boost Mode
The charger device closely monitors the VBUS voltage, as well as HSFET and LSFET current to ensure safe
boost mode operation.
Over-Current Protection
The charger device closely monitors the RBFET (Q1), HSFET (Q2), and LSFET (Q3) current to ensure safe
boost mode operation. During over-current condition, the device will operate in hiccup mode for protection. While
in hiccup mode cycle, the device turns off RBFET for t_{OTG_OCP_OFF} (32ms typical) and turns on RBFET for
t_{OTG_OCP_ON} (260us typical) in an attempt to restart. If the over-current condition is removed, the boost converter
will maintain the RBFET on state and the VBUS OTG output will operate normally. When over-current condition
continues to exist, the device will repeat the hiccup cycle until over-current condition is removed. When over-
current condition is detected, the fault register bit BOOST_FAULT (REG09[6]) is set high to indicate fault in boost
operation. An INT is asserted to the host.
VBUS Over-Voltage Protection
When an adapter plugs in during boost mode, the VBUS voltage will rise above regulation target. Once the
VBUS voltage exceeds V_{OTG_OVP}, the device stops switching and the device exits boost mode. During the over-
voltage, the fault register bit BOOST_FAULT (REG09[6]) is set high to indicate fault in boost operation. An INT is
asserted to the host.
Battery Protection
Battery Over-Voltage Protection (BATOVP)
The battery over-voltage limit is clamped at V_{BAT_OVP} (4% nominal) above the battery regulation voltage. When
battery over voltage occurs, the charger device immediately disables charge. The fault register REG09[5] goes
high and an INT is asserted to the host.
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