BQ27505-J3 Datasheet, PDF (31/44 Pages) Texas Instruments – System-Side Impedance Track™ Fuel Gauge

Not Recommended for New Designs
bq27505-J3
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SLUS986A – OCTOBER 2009 – REVISED FEBRUARY 2010
5.4 TEMPERATURE MEASUREMENT
The bq27505 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.
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 bq27505 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 bq27505 operation, the cell charging voltage must be specified by the user. The default value
for this variable is Charging Voltage Table 4-7.
The bq27505 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 Charge /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 bq27505 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].
When PFC = 1, the bq27505 can indicate when battery temperature has fallen below or risen above
predefined thresholds Suspend Low Temp or Suspend High Temp, respectively. In this mode, the
[XCHG] bit is set to indicate this condition. The [XCHG] bit is cleared 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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