Datasheet

bq27541-V200

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].

Product Folder Links: bq27541-V200