BQ27500 Datasheet, PDF (26/39 Pages) Texas Instruments – System-Side Impedance Track™ Fuel Gauge

bq27500
bq27501
System-Side Impedance Track™ Fuel Gauge
SLUS785 – SEPTEMBER 2007
www.ti.com
5.4 TEMPERATURE MEASUREMENT
The bq27500/1 measures battery temperature via its TS input, in order to supply battery temperature
status information to Impedance Track™ 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
Operation 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 4.1.1 Standard Data Commands for
specific information).
The recommended thermistor circuit uses an external 103AT-type thermistor. Additional circuit information
for connecting this thermistor to the bq27500/1 is shown in the 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. Note: if OT Chg Time =
0 then feature is completely disabled.
When Temperature( ) falls to OT Chg Recovery, the [OTC] of Flags( ) is reset.
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. 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.
5.6 CHARGING AND CHARGE-TERMINATION INDICATION
5.6.1 Detecting Charge Termination
For proper bq27500/1 operation, the cell charging voltage must be specified by the user. The default value
for this variable is Charging Voltage = 4200mV.
The bq27500/1 detects charge termination when (1) during 2 consecutive periods of Current Taper
Window, the AverageCurrent( ) is < Taper Current and (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 Operation
Configuration is set, and RemainingCapacity( ) is set equal to FullChargeCapacity( ).
5.6.2 Charge Inhibit
When PFC = 1, the bq27500/1 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 BAT_GD line 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 PFC = 0 or 2, the bq27500/1 must be queried by the system in order to determine the battery
temperature. At that time, the bq27500/1 will sample the temperature. This saves battery energy when
operating from battery, as periodic temperature updates are avoided during charging mode.
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FUNCTIONAL DESCRIPTION
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