BQ27741-G1_14 Datasheet, PDF (15/39 Pages) Texas Instruments – Single Cell Li-Ion Battery Fuel Gauge with Integrated Protection

bq27741-G1
www.ti.com
SLUSBF2 – JULY 2013
When the battery pack is charged above V_UVPREL, the fuel gauge transitions to Normal Mode.
Normal Mode
In this mode, the protector is fully powered and operational. Both CHG and DSG FETs are closed, while further
operation is determined by the firmware. Protector is continuously checking for all faults.
The CHG or DSG FET may be commanded to be opened via the protector register by the firmware, but it does
not affect protector operation nor changes the mode of operation.
Firmware can also command the fuel gauge to go into shutdown mode based on the command from the host. In
this case, firmware sets the Shutdown bit to indicate intent to go into shutdown mode. The fuel gauge then
transitions to Shutdown Wait Mode.
Shutdown Wait Mode
In this mode, the shutdown bit was set by the firmware and the fuel gauge initiated the shutdown sequence.
The shutdown sequence:
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.
Overcurrent Discharge (OCD) and Short-Circuit Discharge (SCD) Fault 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 configured V_OCD or V_SCD thresholds for longer
than the configured delay.
The fuel gauge enables the fault removal detection circuitry, which monitors load removal. A special high
resistance load is switched in to monitor load presence. The OCD/SCD fault is cleared when the load is
removed, which causes the fuel gauge to transition into Normal Mode.
Overcurrent Charge (OCC) Fault Mode
In this mode, an overcurrent charge (OCC) protection fault is detected when the voltage across the sense
resistor continuously exceeds the configured V_OCC for longer than the configured delay.
The fuel gauge enables the fault removal detection circuitry, which monitors the charger removal. The OCC fault
is cleared once the charger voltage drops below the cell voltage by more than 300 mV, which causes the fuel
gauge to transition to Normal Mode.
Overvoltage Protection (OVP) Fault Mode
In this mode, an overvoltage protection (OVP) fault mode is entered when the voltage on VPWR pin continuously
exceeds the configured V_OVP threshold for longer than the configured delay.
The fuel gauge enables the fault removal detection circuitry, which monitors the charger removal. The OVP fault
is cleared once the charger 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.
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.
Overtemperature Fault Mode
Overtemperature protection is implemented in firmware. Gauging firmware monitors temperature every second
and will open both CHG and DSG FETs if Temperature() > OT Prot Threshold for OT Prot Delay. CHG and DSG
FETs override will be released when Temperature() < OT Prot Recover.
Copyright © 2013, Texas Instruments Incorporated
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