BQ27541 Datasheet, PDF (26/38 Pages) Texas Instruments – Single Cell Li-Ion Battery Fuel Gauge for Battery Pack Integration

bq27541
SLUS861 – DECEMBER 2008 ........................................................................................................................................................................................... www.ti.com
the [CHG] bit of Flags( ) is cleared. Also, if the [RMFCC] bit of Pack Configuration is set, and
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
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].
POWER MODES
The bq27500 has three power modes: NORMAL, SLEEP, and HIBERNATE. In NORMAL mode, the bq27541 is
fully powered and can execute any allowable task. In SLEEP mode the fuel gauge exists in a reduced-power
state, periodically taking measurements and performing calculations. Finally, in HIBERNATE mode, the fuel
gauge is in a low power state, but can be awaken by communication or certain I/O activity.
The relationship between these modes is shown in Figure 3.
NORMAL Mode
The fuel gauge is in NORMAL Mode when not in any other power mode. During this mode, AverageCurrent( ),
Voltage( ) and Temperature( ) measurements are taken, and the interface data set is updated. Decisions to
change states are also made. This mode is exited by activating a different power mode.
Because the gauge consumes the most power in NORMAL mode, the Impedance Track™ algorithm minimizes
the time the fuel gauge remains in this mode.
SLEEP Mode
SLEEP mode is entered automatically if the feature is enabled (Pack Configuration [SLEEP]) = 1) and
AverageCurrent( ) is below the programmable level Sleep Current. Once entry into SLEEP mode has been
qualified, but prior to entering it, the bq27541 performs an ADC autocalibration to minimize offset.
While in SLEEP mode, the fuel gauge can suspend serial communications as much as 4ms by holding the comm
line(s) low. This delay is necessary to correctly process host communication, since the fuel gauge processor is
mostly halted in SLEEP mode.
During the SLEEP mode, bq27541 periodically takes data measurements and updates its data set. However, a
majority of its time is spent in an idle condition.
The bq27541 exits SLEEP if any entry condition is broken, specifically when (1) AverageCurrent( ) rises above
Sleep Current, or (2) a current in excess of I_WAKE through R_SENSE is detected.
FULLSLEEP Mode
FULLSLEEP mode is entered automatically if the feature is enabled by setting the Pack Configuration
[FULLSLEEP] bit in the Control Status register when the bq27541 is in SLEEP mode. The gauge exits the
FULLSLEEP mode when there is any communication activity. Therefore, the execution of SET_FULLSLEEP sets
[FULLSLEEP] bit, but EVSW might still display the bit clear. The FULLSLEEP mode can be verified by
measuring the current consumption of the gauge. In this mode, the high frequency oscialliator is turned off. The
power consumption is further reduced in this mode compared to the SLEEP mode.
FULLSLEEP mode can also be entered by set the Full Sleep Wait Time to be a number larger than 0. The
FULLSLEEP will be entered when the timer counts down to 0. This feature is disabled when the data flash is set
as 0.
During FULLSLEEP mode, the bq27541 periodically takes data measurements and updates its data set.
However, a majority of its time is spent in an idle condition.
The bq27541 exits SLEEP if any entry condition is broken, specifically when (1) AverageCurrent( ) rises above
Sleep Current, or (2) a current in excess of I_WAKE through R_SENSE is detected.
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