BQ27742-G1 Datasheet, PDF (22/46 Pages) Texas Instruments – Single-Cell Li-Ion Battery Fuel Gauge with Programmable Hardware Protection

bq27742-G1
SLUSBV9C – MARCH 2014 – REVISED FEBRUARY 2016
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Device Functional Modes (continued)
7.4.1.2 OVERVOLTAGE Mode
In this mode, an overvoltage protection (OVP) fault mode is entered when the voltage on the V_BAT pin
continuously exceeds the V_OVP threshold for longer than the t_OVP delay time. At this point, the fuel gauge enables
the fault recovery detection circuitry, which monitors the PACKP pin for charger removal. The OVP fault is
cleared once the pack voltage drops below the cell voltage by more than 300 mV and the cell voltage drops
below V_OVPREL, which causes the fuel gauge to transition to NORMAL mode.
7.4.1.3 UNDERVOLTAGE Mode
In this mode, an undervoltage protection (UVP) fault mode is entered when the voltage on the V_BAT pin
continuously falls below the V_UVP threshold for longer than the t_UVP delay time. The fuel gauge then enables the
charger attach detection circuitry and, if no charger is found, sends the fuel gauge into ANALOG SHUTDOWN
mode to minimize power consumption and avoid further discharge of the battery. The UVP fault is cleared once
charger attach is detected and the cell voltage rises above V_UVPREL, which causes the fuel gauge to transition to
NORMAL mode.
The fuel gauge can enter this mode from LOW VOLTAGE CHARGING mode when the battery pack is being
charged from a deeply discharged state or from NORMAL mode when the battery pack is being discharged past
the UVP threshold.
7.4.1.4 OVERCURRENT CHARGE Mode
In this mode, an overcurrent in charge (OCC) fault mode is entered when the voltage across the sense resistor
continuously exceeds the V_OCC threshold for longer than the configured t_OCC delay time. Recovery occurs when
the PACKP voltage drops to more than 300 mV below the cell voltage, indicating charger removal.
7.4.1.4.1 OVERCURRENT DISCHARGE and SHORT-CIRCUIT DISCHARGE Mode
In this mode, a short-circuit discharge (SCD) or overcurrent discharge (OCD) protection fault is detected when
the voltage across the sense resistor continuously exceeds the V_OCD or V_SCD thresholds for longer than the t_OCD
or t_SCDdelay times. Recovery occurs when the PACKP voltage rises to within 300 mV of the cell voltage,
indicating load removal.
7.4.1.5 SHUTDOWN WAIT Mode
A transition to this mode occurs when the host sends the SET_SHUTDOWN command and the fuel gauge
subsequently initiated the shutdown sequence.
The shutdown sequence is as follows:
1. Open both CHG and DSG FETs.
2. Determine if any faults are set. If any faults are set, then go back to NORMAL mode.
3. Wait for charger removal. Once the charger is removed, turn off the LDO, which puts the fuel gauge into
ANALOG SHUTDOWN mode.
7.4.1.5.1 ANALOG SHUTDOWN State
In this mode, the fuel gauge is completely powered down and no portions of the device are functional. Once the
charger is connected, the fuel gauge will transition into either LOW VOLTAGE CHARGING mode (if below the
power-on reset voltage) or NORMAL mode (if above the POR voltage and no faults are detected).
7.4.1.6 LOW VOLTAGE CHARGING State
In this mode, the fuel gauge shorts the CHG FET gate to PACKP pin if the cell voltage is above the V_LVDET
threshold, allowing the battery to be trickle charged with the CHG FET biased in the ohmic region. If below the
aforementioned threshold, low voltage charging is prohibited for safety reasons and the cell will likely be
permanently unrecoverable due to being dangerously depleted.
7.4.2 Firmware Control of Protector
The firmware has control to open the CHG FET or DSG FET independently by overriding hardware control.
However, it has no control to close the CHG FET or DSG FET and can only disable the FET override.
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