BQ27541-V200_17 Datasheet, PDF (28/46 Pages) Texas Instruments – Single Cell Li-Ion Battery Fuel Gauge for Battery Pack Integration

bq27541-V200
Not Recommended for New Designs
SLUSA11B – FEBRUARY 2010 – REVISED SEPTEMBER 2013
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TEMPERATURE MEASUREMENT AND THE TS INPUT
The bq27541 measures battery temperature via the TS input, in order to supply battery temperature status
information to the fuel gauging algorithm and charger-control sections of the gauge. Alternatively, the gauge can
also measure internal temperature via its on-chip temperature sensor, but only if the [TEMPS] bit of Pack
Configuration register is cleared.
Regardless of which sensor is used for measurement, a system processor can request the current battery
temperature by calling the Temperature( ) function (see Section Standard Data Commands, for specific
information).
The thermistor circuit requires the use of an external 10KΩ thermistor with negative temperature coefficients,
such as Semitec 103AT-type thermistor that connects between the Vcc and TS pins. Additional circuit
information for connecting the thermistor to the bq27541 is shown in the Reference Schematic.
OVER-TEMPERATURE INDICATION
Over-Temperature: 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, the feature is disabled.
Over-Temperature: 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, the feature is disabled.
CHARGING AND CHARGE TERMINATION INDICATION
Detection Charge Termination
For proper bq27541 operation, the cell charging voltage must be specified by the user. The default value for this
variable is in the data flash Charging Voltage.
The bq27541 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 >
0.25mAh / 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 Pack Configuration is set, then
RemainingCapacity( ) is set equal to FullChargeCapacity( ). When TCA_Set is set to -1, it disables the use of the
charger alarm threshold. In that case, TerminateCharge is set when the taper condition is detected. When
FC_Set is set to -1, it disables the use of the full charge detection threshold. In that case, FullCharge is not set
until the taper condition is met.
Charge Inhibit and Suspend
The bq27541 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 [CHG_INH] of
Flags( ) is made high to indicate this condition, and is 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 the battery temperature has fallen below or risen above predefined thresholds Suspend Temperature
Low or Suspend Temperature High, respectively. In this mode, the [XCHG] of Flags( ) is made high to indicate
this condition, and is returned to its low state, once battery temperature returns to the range [Charge Inhibit
Temp Low + Temp Hys, Charge Inhibit Temp High – Temp Hys].
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