BQ27500-V120 Datasheet, PDF (27/36 Pages) Texas Instruments – System-Side Impedance Track™ Fuel Gauge

bq27500-V120
www.ti.com
System-Side Impedance Track™ Fuel Gauge
SLUS880 – OCTOBER 2008
5.7.3 SLEEP+ MODE
Compared to the SLEEP mode, SLEEP+ mode has the high frequency oscillator in operation. The
communication delay could be eliminated. The SLEEP+ is entered automatically if the feature is enabled
(Operation Configuration [SNOOZE] = 1) and AverageCurrent( ) is below the programmable level Sleep
Current.
During SLEEP+ mode, the bq27500 periodically takes data measurements and updates its data set.
However, a majority of its time is spent in an idle condition. The bq27500 exits SLEEP+ if any entry
condition is broken, specifically when (1) any communication activity with the gauge, or (2)
AverageCurrent( ) rises above Sleep Current, or (3) a current in excess of IWAKE through RSENSE is
detected.
5.7.4 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 performs a Coulomb Counter autocalibration to
minimize offset.
During SLEEP mode, the bq27500 periodically takes data measurements and updates its data set.
However, a majority of its time is spent in an idle condition.
The bq27500 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
SCL line low. This delay is necessary correctly process host communication, since the fuel gauge
processor is mostly halted while in SLEEP mode.
5.7.5 HIBERNATE MODE
HIBERNATE mode should be used when the system equipment needs to enter a low-power state, and
minimal gauge power consumption is required. This mode is ideal when a system equipment 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 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.
• HIBERNATE due to the load current. If the load current drops to certain level, the fuel gauge should
also enter low power mode. When 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. The gauge remains in HIBERNATE mode
until the system issues a direct I²C command to the gauge or a POR occurs. I²C communication that is
not directed to the gauge does not wake the gauge.
During the HIBERNATE mode the BAT_GD is negated (no battery charging/discharging). This
prevents a charger application from inadvertently charging the battery before an OCV reading can be
taken. It is the system’s responsibility to wake the bq27500 after it has gone into HIBERNATE mode.
After waking, the gauge can proceed with the initialization of the battery information (OCV, profile
selection, etc.)
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FUNCTIONAL DESCRIPTION
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