BQ27541-V200_1007 Datasheet, PDF (30/43 Pages) Texas Instruments – Single Cell Li-Ion Battery Fuel Gauge for Battery Pack Integration

bq27541-V200
SLUSA11 – FEBRUARY 2010
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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, 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.
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 setting 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 IWAKE through RSENSE is detected.
While in FULLSLEEP mode, the fuel gauge can suspend serial communications as much as 4ms by holding the
comm line(s) low. This delay is necessary correctly process host communication, since the fuel gauge processor
is mostly halted in SLEEP mode.
HIBERNATE MODE
HIBERNATE mode should be used when the host system needs to enter a very low-power state, and minimal
gauge power consumption is required. This mode is ideal when the host is set to its own HIBERNATE,
SHUTDOWN, or OFF modes. The fuel gauge can enter HIBERNATE due to either low cell voltage or low load
current.
• HIBERNATE due to the load current. If the fuel gauge enters the HIBERNATE mode due to the load current,
the [HIBERNATE] bit of the CONTROL_STATUS register must be set. The gauge waits to enter HIBERNATE
mode until it has taken a valid OCV measurement and the magnitude of the average cell current has fallen
below Hibernate Current.
• HIBERNATE due to the cell voltage. When the cell voltage drops below the Hibernate Voltage and a valid
OCV measurement has been taken, the fuel gauge enters HIBERNATE mode. The [HIBERNATE] bit of the
CONTROL register has no impact for the fuel gauge to enter the HIBERNATE mode. If the [SHUTDOWN] bit
of CONTROL _STATUS is also set, the SE pin will be released in the state shown by Table 11; thereby,
allowing an optional external circuit to remove power from the gauge LDO.
The gauge will remain in HIBERNATE mode until any communication activity appears on the communication
lines Upon exiting HIBERNATE mode, the [HIBERNATE] bit of CONTROL_STATUS is cleared. Since any
communication activity wakes up the gauge from HIBERNATE mode, the host is required to set the
[HIBERNATE] bit of the CONTROL_STATUS register to allow gauge to re-enter HIBERNATE mode.
Because the fuel gauge is dormant in HIBERNATE mode, the battery should not be charged or discharged in this
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