BQ27500_08 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
SLUS785D – SEPTEMBER 2007 – REVISED APRIL 2008
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.
While in SLEEP mode, the fuel gauge can suspend serial communications as much as 4ms by holding the
SDA pin low. This delay is necessary correctly process host communication, since the fuel gauge
processor is mostly halted while in SLEEP mode.
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 begins, which includes: 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 wakes up to process the command, then returns to the halted state awaiting battery
insertion.
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FUNCTIONAL DESCRIPTION
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