BQ27350 Datasheet, PDF (22/33 Pages) Texas Instruments – Single Cell Li-Ion Battery Manager With Impedance Track Fuel Gauge Technology

bq27350
Single Cell Li-Ion Battery Manager
With Impedance Track Fuel Gauge Technology
SLUS754 – MARCH 2007
www.ti.com
When an external thermistor input is used, TOUT (pin 7) is used to power the thermistor and TS (pin 3) to
measure the thermistor voltage. The bq27350 then correlates the voltage to temperature assuming the
thermistor is a Semitec 103AT or similar device.
5.4 OVER-TEMPERATURE INDICATION
The bq27350 can set safety flag indications based on measure temperature both in charge and discharge
states.
Over-Temperature: Charge
If during charging, Temperature( ) exceeds the threshold of OT Chg for a period of OT Chg Time and
AverageCurrent( ) > Chg Current Threshold, then the [OTC] bit of Flags( ) is set. Note: if OT Chg Time =
0 then feature is completely disabled.
When Temperature( ) falls below OT Chg Recovery, the [OTC] of Flags( ) is reset.
Over-Temperature: Discharge
If, during discharging, Temperature( ) exceeds the threshold of OT Dsg for a period of OT Dsg Time, and
AverageCurrent( ) ≤ -Dsg Current Threshold, then the [OTD] bit of Flags( ) is set. Note: if OT Dsg Time
= 0 then feature is completely disabled.
When Temperature( ) falls below OT Dsg Recovery, the [OTD] bit of Flags( ) is reset.
5.5 CHARGING AND CHARGE TERMINATION INDICATION
For proper bq27350 operation, the cell charging voltage must be specified by the user. The default value
for this variable is Charging Voltage = 4200mV.
The bq27350 detects charge termination when (1) during 2 consecutive periods of Current Taper
Window, the AverageCurrent( ) is < Taper Current and (2) during the same periods, the accumulated
change in capacity > 0.25mAh /Taper Current Window and (3) Voltage( ) > Charging Voltage -
Charging Taper Voltage. When this occurs, the [FC] bit of Flags( ) is set and [CHG] bit is cleared. Also, if
the [RMFCC] bit of Pack Configuration is set, then RemainingCapacity( ) is set equal to
FullChargeCapacity( )
5.6 POWER MODES
The bq27350 has four power modes: NORMAL, SLEEP, HIBERNATE, and SHUTDOWN (in descending
order of power consumption). In NORMAL mode, the bq27350 is fully powered and can execute any
allowable task. In SLEEP mode the gas gauge exists in a reduced-power state, periodically taking
measurements and performing calculations. In HIBERNATE mode the gas gauge is in its lowest power
state, only to be woken by communications activity or an increase in the magnitude of battery current.
Finally in SHUTDOWN mode, all bq27350 circuits are turned off and power is removed from the device;
the IC can be restarted by reapplying sufficient voltage to the device.
The relationship between these modes is shown in Figure 5-1. Details are described in the sections that
follow.
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FUNCTIONAL DESCRIPTION
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