BQ24618_15 Datasheet, PDF (21/43 Pages) Texas Instruments – System Power Selector and Low

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bq24618
SLUSA55B – OCTOBER 2010 – REVISED APRIL 2015
Feature Description (continued)
8.3.13 Input Overvoltage Protection (ACOV)
ACOV provides protection to prevent system damage due to high input voltage. Once the adapter voltage
reaches the ACOV threshold, charge is disabled and the system is switched to the battery instead of the adapter.
8.3.14 Input Undervoltage Lockout (UVLO)
The system must have a minimum VCC voltage to allow proper operation. This VCC voltage could come from
either the input adapter or the battery, because a conduction path exists from the battery to VCC through the
high-side NMOS body diode. When VCC is below the UVLO threshold, all circuits on the IC are disabled, and the
gate-drive bias to ACFET and BATFET is disabled.
8.3.15 Battery Overvoltage Protection
The converter does not allow the high-side FET to turn on until the BAT voltage goes below 102% of the
regulation voltage. This allows one-cycle response to an overvoltage condition, such as occurs when the load is
removed or the battery is disconnected. An 8-mA current sink from SRP to GND is on only during charge and
allows discharging the stored output inductor energy that is transferred to the output capacitors. BATOVP also
suspends the safety timer.
8.3.16 Cycle-by-Cycle Charge Overcurrent Protection
The charger has secondary cycle-to-cycle overcurrent protection. It monitors the charge current, and prevents
the current from exceeding 160% of the programmed charge current. The high-side gate drive turns off when the
overcurrent is detected, and automatically resumes when the current falls below the overcurrent threshold.
8.3.17 Thermal Shutdown Protection
The QFN package has low thermal impedance, which provides good thermal conduction from the silicon to the
ambient, to keep junction temperature low. As an added level of protection, the charger converter turns off and
self-protects whenever the junction temperature exceeds the TSHUT threshold of 145°C. The charger stays off
until the junction temperature falls below 130°C; then the charger soft-starts again if all other charge enabling
conditions are valid. Thermal shutdown also suspends the safety timer.
8.3.18 Temperature Qualification
The controller continuously monitors battery temperature by measuring the voltage between the TS pin and
GND. A negative temperature coefficient thermistor (NTC) and an external voltage divider typically develop this
voltage. The controller compares this voltage against its internal thresholds to determine if charging is allowed.
To initiate a charge cycle, the battery temperature must be within the V_LTF and V_HTF thresholds. If battery
temperature is outside of this range, the controller suspends charge and the safety timer and waits until the
battery temperature is within the V_LTF to V_HTF range. During the charge cycle, the battery temperature must be
within the V_LTF and V_TCO thresholds. If battery temperature is outside of this range, the controller suspends
charge and waits until the battery temperature is within the V_LTF to V_HTF range. The controller suspends charge
by turning off the PWM charge FETs. Figure 14 summarizes the operation.
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