BQ27500-V120 Datasheet, PDF (25/36 Pages) Texas Instruments – System-Side Impedance Track™ Fuel Gauge

bq27500-V120
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5.5.2 Overtemperature: Discharge
System-Side Impedance Track™ Fuel Gauge
SLUS880 – OCTOBER 2008
If during discharging, Temperature( ) reaches 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. When Temperature( )
falls to OT Dsg Recovery, the [OTD] bit of Flags( ) is reset.
If OT Dsg Time = 0, then feature is completely disabled.
5.6 CHARGING AND CHARGE-TERMINATION INDICATION
5.6.1 Detecting Charge Termination
For proper bq27500 operation, the cell charging voltage must be specified by the user. The default value
for this variable is Charging Voltage = 4200 mV.
The bq27500 detects charge termination when (1) during 2 consecutive periods of Current Taper
Window, the AverageCurrent( ) is < Taper Current, (2) during the same periods, the accumulated
change in capacity > 0.25 mAh /Current Taper Window, and (3) Voltage( ) > Charging Voltage – Taper
Voltage. When this occurs, the [CHG] bit of Flags( ) is cleared. Also, if the [RMFCC] bit of Operation
Configuration is set, then RemainingCapacity( ) is set equal to FullChargeCapacity( ).
5.6.2 Charge Inhibit
When PFC = 1, the bq27500 can indicate when battery temperature has fallen below or risen above
predefined thresholds (Charge Inhibit Temp Low and Charge Inhibit Temp High, respectively). In this
mode, the BAT_GD line is made high to indicate this condition then returned to its low state, once battery
temperature returns to the range [Charge Inhibit Temp Low + Temp Hys, Charge Inhibit Temp High –
Temp Hys].
When PFC = 0 or 2, the bq27500 must be queried by the system in order to determine the battery
temperature. At that time, the bq27500 samples the temperature. This saves battery energy when
operating from battery, as periodic temperature updates are avoided during charging mode.
5.7 POWER MODES
The bq27500 has different power modes: NORMAL, SLEEP, HIBERNATE, and BAT INSERT CHECK. In
NORMAL mode, the bq27500 is fully powered and can execute any allowable task. In SLEEP mode, the
fuel gauge exists in a reduced-power state, periodically taking measurements and performing calculations.
In HIBERNATE mode, the fuel gauge is in its lowest power state, but can be woken up by communication
activity or certain I/O activity. Finally, the BAT INSERT CHECK mode is a powered-up, but low-power
halted state, where the bq27500 resides when no battery is inserted into the system.
The relationship between these modes is shown in Figure 5-1.
5.7.1 BAT-INSERT-CHECK MODE
This mode is a halted-CPU state that occurs when an adapter or other power source is present to power
the bq27500 (and system), yet no battery has been detected. When battery insertion is detected, a series
of initialization activities begins, which includes: OCV measurement, asserting the BAT_GD pin, and
selecting the appropriate battery profiles. The initialization time is less than 2 seconds.
Some commands issued by a system processor can be processed while the bq27500 is halted in this
mode. The gauge wakes up to process the command, then returns to the halted state awaiting battery
insertion.
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FUNCTIONAL DESCRIPTION
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