BQ77908A Datasheet, PDF (20/52 Pages) Texas Instruments – Multi-Cell Lithium-Ion/Polymer Precision Protector

bq77908A
SLUSAV5 – FEBRUARY 2012
www.ti.com
Table 2. Fault Detection, Action, and Recovery Condition Summary
Fault Condition
Fault Detection
Parameter
Filter Time
CELL
OVERVOLTAGE
Any cell > V_OV
t_OV
Action Taken
FET
CHG
DSG
MODE
OFF
OV FAULT protection state
ON _{EXT CHGR DISABLE}
(TS pin→low)
EEPROM Config
(if Applicable)
OV_TS_CTRL = 0
OV_TS_CTRL = 1
CELL UNDER-
VOLTAGE
Any cell < V_UV
t_UV
OFF ^{(1) (2)}
OFF
UV FAULT protection
state ⁽³⁾
OFF ^{(5) (2)}
OFF
UV FAULT protection
state ⁽³⁾
UV_REC bit = 0
UV_REC bit = 1
PACK OVER-
TEMPERATURE
Pack temperature out
of range,
V_TS < V_HOT
(1-2) × t_{THERM_CHECK}
OVERCURRENT
IN DISCHARGE
(V_SC – VSS) > V_OCD
t_OCD
OFF
OFF
OFF
SHORT CIRCUIT
IN DISCHARGE
(V_SC – VSS) > V_SCD
t_SCD
SHORT CIRCUIT
IN CHARGE
(V_SS – V_SC) > V_SCC
t_SCC
OPEN
THERMISTOR
V_TS > V_{TH_OPEN}
(1 to 2) × t_{THERM_CHECK}
SHORTED
THERMISTOR
OPEN-CELL
INPUT
V_TS < V_{TH_SHORT}
(1 to 2) × t_{THERM_CHECK}
Cell-to-pin impedance (1 to 2) ×
> R_{OPEN_CELL}
t_{OPEN_CELL_CHECK}
OFF
OFF
OFF
OFF
OFF
OFF
OFF
OT FAULT protection state
TMP_REC bit = 0
TMP_REC bit = 1
OFF
OCD FAULT protection
state
SOR bit = 0
SOR bit = 1
OFF
SCD FAULT protection
state
SOR bit = 0
SOR bit = 1
OFF
SCD FAULT protection
state
N/A
OPEN
OFF THERM/UNDERTEMP
N/A
protection state
OFF
SHUTDOWN (low-power
state)
OFF
SHUTDOWN (low-power
state)
Recovery Conditions
All cells < OV-hyst
1) Both FETS ON when all cells >UV +
hyst ⁽⁴⁾
2) CHG FET enabled immediately if
charger detected
1) Both FETs enabled when all cells
>UV + hyst AND load removed
2) CHG FET enabled immediately if
charger detected
V_TS > VHOT + hysteresis⁽⁶⁾
V_TS > VHOT + hysteresis⁽⁶⁾ and load
removed
Both ON when load removed
Both ON when load removed AND
charger detected
Both ON when load removed
Both ON when load removed AND
charger detected
Charger removed
V_TS < V_{TH_OPEN} – V_{TH_HYST(6)}
Charger detected and V_TS > V_{TH_SHORT}
+ V_{TH_HYST} ^(6)(7)(8)
Charger detected and open-cell
condition absent > filter time⁽⁹⁾
(1) The LDO is turned off in the SHUTDOWN mode. When the LDO is disabled, the CHG FET drive output is OFF by default, as all outputs
of the device are disabled.
(2) Regardless of EEPROM setting, if a battery pack in the UV protection state is inserted into a charger (charger presence is detected), the
CHG FET is turned ON to allow recharge of the pack. The DSG FET is turned on after UV recovery, as noted in Table 2 (conditions
based on EEPROM setting).
(3) a) If UV_REC_DLY = 1 and any cell remains < UV + hyst for longer than 8 seconds, the device enters SHUTDOWN mode and requires
insertion into charger to recover. If UV_REC_DLY = 0, the device does not enter SHUTDOWN mode from the UV FAULT protection
state.
b) The LDO is turned off in the SHUTDOWN mode. Charger insertion is required to recover from the SHUTDOWN mode.
CAUTION: Care should be taken when using UV_REC = 0, because the power MOSFETs can oscillate when high load currents cause
repeated cell UV conditions, which could result in overheating of cells or MOSFETs.
(4) If the UV_HYST_INH bit = 1, then the hysteresis threshold is inhibited and recovery occurs whenever the cells exceed the UV threshold
(without hysteresis). If UV_HYST_INH = 1, the UV_REC bit should also be configured = 1. Otherwise, UV fault/recovery modes may
chatter without hysteresis.
(5) If the LDO is left ON, the CHG FET is disabled when the fault condition occurs and re-enabled as soon as a charger is attached. The
DSG FET does not re-enable until the UV condition is cleared (Vcell > Vuv + hysteresis).
(6) Recovery occurs within t_{THERM_CHECK} after recovery conditions are met.
(7) If a thermistor short occurs while charger is not detected, the FETs initially are re-enabled when charger is detected. If short condition is
still present t_{THERM_CHECK} after charger detection and CHG_TMP_DIS = 0, the FETs re-open until the short condition is removed. If
CHG_TMP_DIS = 1, the FETs remain enabled regardless of the short condition.
(8) If a charger is presently detected when the shorted thermistor fault is registered, the LDO does not shut off. Within 0 to 4 seconds after
the short is removed, the FETs re-enable and the device recovers. However, if the charger is disconnected after the short is removed,
but before the FETs are re-enabled, the device will shut down with the LDO off and require charger detection for recovery.
(9) If an open-cell fault occurs while a charger is detected, the device does not shut down. However, the device does shut down if the
charger is later disconnected while the open-cell condition is still present. If the charger is disconnected after the open-cell condition is
removed, the device recovers (i.e., FETs are re-enabled). Following a shutdown caused by an open-cell condition, the FETs initially
re-enable when a charger is detected. However, if the open-cell condition is still present, the FETs re-open after the filter time.
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