BQ27520-G2 Datasheet, PDF (32/47 Pages) Texas Instruments – System-Side Impedance Track™ Fuel Gauge With Integrated LDO

bq27520-G2
SLUSAB7A – MARCH 2011 – REVISED AUGUST 2011
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5.4 TEMPERATURE MEASUREMENT
The bq27520-G2 measures battery temperature via its TS input, in order to supply battery temperature
status information to the fuel gauging algorithm and charger-control sections of the gauge. Alternatively, it
can also measure internal temperature via its on-chip temperature sensor, but only if the [TEMPS] bit of
the Operation Configuration register is cleared. The [GNDSEL] bit of Operation Configuration B register
selects the ground reference of the ADC converter for temperature measurement. A third option is
enabled if the [WRTEMP] bit of Operation Configuration B is set. This allows a host processor to write the
temperature measurement directly to the bq27520-G2 instead of the gauge making its own temperature
measurements.
Regardless of which sensor is used for measurement, a system processor can request the current battery
temperature by calling the Temperature( ) function (see Section 4.1.1, Standard Data Commands, for
specific information).
The thermistor circuit requires the use of an external NTC 103AT-type thermistor. Additional circuit
information for connecting this thermistor to the bq27520-G2 is shown in Section 8, Reference Schematic.
5.5 OVERTEMPERATURE INDICATION
5.5.1 Overtemperature: Charge
If during charging, Temperature( ) reaches 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. When Temperature( )
falls to OT Chg Recovery, the [OTC] of Flags( ) is reset.
If OT Chg Time = 0, then the feature is completely disabled.
5.5.2 Overtemperature: Discharge
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 bq27520-G2 operation, the cell charging voltage must be specified by the user. The default
value for this variable is Charging Voltage Table 4-7.
The bq27520-G2 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 > Min Taper Capacity /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 and Suspend
The bq27520-G2 can indicate when battery temperature has fallen below or risen above predefined
thresholds Charge Inhibit Temp Low or Charge Inhibit Temp High, respectively. In this mode, the
[CHG_INT] bit is set and the BAT_GD pin is deserted to indicate this condition. The [CHG_INT] bit is
cleared and the BAT_GD pin is asserted once the battery temperature returns to the range [Charge
Inhibit Temp Low + Temp Hys, Charge Inhibit Temp High – Temp Hys].
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FUNCTIONAL DESCRIPTION
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