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5.4 TEMPERATURE MEASUREMENT
5.5 OVERTEMPERATURE INDICATION
5.5.1 Overtemperature: Charge
5.5.2 Overtemperature: Discharge
5.6 CHARGING AND CHARGE-TERMINATION INDICATION
5.6.1 Detecting Charge Termination
5.6.2 Charge Inhibit
bq27500
bq27501
System-Side Impedance Track™ Fuel Gauge
SLUS785 – SEPTEMBER 2007
The bq27500/1 measures battery temperature via its TS input, in order to supply battery temperaturestatus information to Impedance Track™ and charger control sections of the gauge. Alternatively, it canalso measure internal temperature via its on-chip temperature sensor, but only if the [TEMPS] bit ofOperation Configuration register is cleared.
Regardless of which sensor is used for measurement, a system processor can request the current batterytemperature by calling the Temperature( ) function (see Section 4.1.1 Standard Data Commands forspecific information).
The recommended thermistor circuit uses an external 103AT-type thermistor. Additional circuit informationfor connecting this thermistor to the bq27500/1 is shown in the Section 8 Reference Schematic.
If during charging, Temperature( ) reaches the threshold of OT Chg for a period of OT Chg Time andAverageCurrent( ) >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 to OT Chg Recovery, the [OTC] of Flags( ) is reset.
If during discharging, Temperature( ) reaches the threshold of OT Dsg for a period of OT Dsg Time, andAverageCurrent( ) ≤-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 to OT Dsg Recovery, the [OTD] bit of Flags( ) is reset.
For proper bq27500/1 operation, the cell charging voltage must be specified by the user. The default valuefor this variable is Charging Voltage = 4200mV.
The bq27500/1 detects charge termination when (1) during 2 consecutive periods of Current TaperWindow,the AverageCurrent( ) is < Taper Current and (2) during the same periods, the accumulatedchange in capacity > 0.25mAh / Current Taper Window and (3) Voltage( ) >Charging Voltage – TaperVoltage. When this occurs, the [CHG] bit of Flags( ) is cleared. Also, if the [RMFCC] bit of OperationConfiguration is set, and RemainingCapacity( ) is set equal to FullChargeCapacity( ).
When PFC = 1, the bq27500/1 can indicate when battery temperature has fallen below or risen abovepredefined thresholds ( Charge Inhibit Temp Low and Charge Inhibit Temp High, respectively). In thismode, the BAT_GD line is made high to indicate this condition, and is returned to its low state, oncebattery temperature returns to the range [Charge Inhibit Temp Low + Temp Hys, Charge Inhibit TempHigh – Temp Hys].
When PFC = 0 or 2, the bq27500/1 must be queried by the system in order to determine the batterytemperature. At that time, the bq27500/1 will sample the temperature. This saves battery energy whenoperating from battery, as periodic temperature updates are avoided during charging mode.
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