BQ27505-J4 Datasheet, PDF (29/38 Pages) Texas Instruments – System-Side Impedance Track™ Fuel Gauge

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bq27505-J4
SLVSA40 – DECEMBER 2009
Regardless of which sensor is used for measurement, a system processor can request the current battery
temperature by calling the Temperature( ) function (see 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 bq27505-J4 is shown in 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 Chg Recovery, the [OTC] 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-J4 operation, the cell charging voltage must be specified by the user. The default
value for this variable is Charging Voltage in Table 4-7.
The bq27505-J4 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 Operation
Configuration is set, and RemainingCapacity( ) is set equal to FullChargeCapacity( ).
5.6.2 Charge Inhibit
When PFC = 1, the bq27505-J4 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 bq27505-J4 must be queried by the system in order to determine the battery
temperature. At that time, the bq27505-J4 will sample the temperature. This saves battery energy when
operating from battery, as periodic temperature updates are avoided during charging mode.
5.7 POWER MODES
The bq27505-J4 has different power modes: BAT INSERT CHECK, NORMAL, SLEEP, SLEEP+ and
HIBERNATE. In NORMAL mode, the bq27505-J4 is fully powered and can execute any allowable task. In
SLEEP+ mode, both low frequency and high frequency oscillators are active. Although the SLEEP+ has
higher current consumption than the SLEEP mode, it is also a reduced power mode. In SLEEP mode, the
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FUNCTIONAL DESCRIPTION
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