BQ27500 Datasheet, PDF (27/39 Pages) Texas Instruments – System-Side Impedance Track™ Fuel Gauge

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bq27500
bq27501
System-Side Impedance Track™ Fuel Gauge
SLUS785 – SEPTEMBER 2007
5.7 POWER MODES
The bq27500/1 has four power modes: NORMAL, SLEEP, HIBERNATE, and BAT INSERT CHECK. In
NORMAL mode, the bq27500/1 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.
In HIBERNATE mode, the fuel gauge is in its lowest power state, but can be woken up by communication
activity or certain I/O activity. Finally, the BAT INSERT CHECK mode is a powered-up, but low-power
halted, state, where the bq27500/1 resides when no battery is inserted into the system.
The relationship between these modes is shown in Figure 5-2.
5.7.1 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.
5.7.2 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 bq27500/1 performs an ADC autocalibration to minimize
offset.
During SLEEP mode, the bq27500/1 periodically takes data measurements and updates its data set.
However, a majority of its time is spent in an idle condition.
The bq27500/1 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.
5.7.3 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 bq27500/1 (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 bq27500/1 is halted in this
mode. The gauge will wake up to process the command, then return to the halted state awaiting battery
insertion.
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FUNCTIONAL DESCRIPTION
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