BQ27505 Datasheet, PDF (31/42 Pages) Texas Instruments – System-Side Impedance Track™ Fuel Gauge

Not Recommended for New Designs
bq27505
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SLUS884 – FEBRUARY 2009
5.7 POWER MODES
The bq27505 has different power modes: BAT INSERT CHECK, NORMAL, SLEEP, SLEEP+ and
HIBERNATE. In NORMAL mode, the bq27505 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
fuel gauge turns off the high frequency oscillator and exists in a reduced-power state, periodically taking
measurements and performing calculations. In HIBERNATE mode, the fuel gauge is in a very low power
state, but can be woken up by communication or certain I/O activity. Finally, the BAT INSERT CHECK
mode is a powered-up, but low-power halted, state, where the bq27505 resides when no battery is
inserted into the system.
The relationship between these modes is shown in Figure 5-1.
5.7.1 BAT INSERT CHECK Mode
This mode is a halted-CPU state that occurs when an adapter, or other power source, is present to power
the bq27505 (and system), yet no battery has been detected. When battery insertion is detected, a series
of initialization activities begin, which include: OCV measurement, setting the BAT_GD pin, and selecting
the appropriate battery profiles.
Some commands, issued by a system processor, can be processed while the bq27505 is halted in this
mode. The gauge will wake up to process the command, then return to the halted state awaiting battery
insertion.
5.7.2 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.
5.7.3 SLEEP MODE
SLEEP mode is entered automatically if the feature is enabled (Operation 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 bq27505 performs an coulomb counter autocalibration to
minimize offset.
During SLEEP mode, the bq27505 periodically takes data measurements and updates its data set.
However, a majority of its time is spent in an idle condition.
The bq27505 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.
In the event that a battery is removed from the system while a charger is present (and powering the
gauge), Impedance Track™ updates are not necessary. Hence, the fuel gauge enters a state that checks
for battery insertion and does not continue executing the Impedance Track™ algorithm.
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FUNCTIONAL DESCRIPTION
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