BQ27425-G2_14 Datasheet, PDF (24/35 Pages) Texas Instruments – System-Side Impedance Track™ Fuel Gauge With Integrated Sense Resistor

bq27425-G2
SLUSB23A – OCTOBER 2012 – REVISED FEBRUARY 2013
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POR and INITIALIZATION Modes
Upon Power On Reset (POR), the fuel gauge copies ROM-based configuration defaults to RAM and begins
INITIALIZATION mode where essential data is initialized and will remain in INITIALIZATION mode as halted-
CPU state when an adapter, or other power source is present to power the bq27425 (and system), yet no battery
has been detected. The occurrence of POR or a Control( ) RESET subcommand will set the Flags( ) [ITPOR]
status bit to indicate that RAM has returned to ROM default data. When battery insertion is detected, a series of
initialization activities begin including an OCV measurement. In addition CONTROL_STATUS[QMAX_UP] and
[RES_UP] bits are cleared to allow fast learning of Qmax and impedance.
Some commands, issued by a system processor, can be processed while the bq27425 is halted in this mode.
The gauge will wake up to process the command, and then return to the halted state awaiting battery insertion.
The current consumption of INITIALIZATION mode is similar to NORMAL mode.
CONFIG UPDATE Mode
If the application requires different configuration data for the bq27425. The host can update both NVM and RAM
based parameters using the Control( ) SET_CFGUPDATE subcommand to enter CONFIG UPDATE mode as
indicated by the Flags( ) [CFGUPMODE] status bit. In this mode, fuel gauging is suspended while the host uses
the Extended Data Commands to modify the configuration data blocks. To resume fuel gauging, the host sends a
Control( ) SOFT_RESETsubcommand to exit CONFIG UPDATE mode and clear both Flags( ) [ITPOR] and
[CFGUPMODE] bits. After a timeout of approximately 240 seconds (4 minutes), the gauge will automatically exit
CONFIG UPDATE mode if it has not received a SOFT_RESET subcommand from the host.
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 once per second, 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.
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 (default = 10mA). Once entry into SLEEP
mode has been qualified, but prior to entering it, the bq27425 performs an ADC autocalibration to minimize
offset.
During SLEEP mode, the bq27425 periodically takes data measurements and updates its data set. However, a
majority of its time is spent in an idle condition.
The bq27425 exits SLEEP if any entry condition is broken, specifically when: AverageCurrent( ) rises above
Sleep Current (default = 10mA).
HIBERNATE Mode
HIBERNATE mode could be used when the system equipment needs to enter a very 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.
Before the fuel gauge can enter HIBERNATE mode, the system must set the [HIBERNATE] bit of the
CONTROL_STATUS register. 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 can
also enter HIBERNATE mode if the cell voltage falls below Hibernate Voltage. The gauge will remain in
HIBERNATE mode until the system issues a direct I²C command to the gauge. I²C communication that is not
directed to the gauge will only briefly wake it up and the gauge immediately returns to HIBERNATE mode.
It is the system’s responsibility to wake the bq27425 after it has gone into HIBERNATE mode and to prevent a
charger from charging the battery before the [OCVTAKEN] bit is set which signals an OCV reading is taken. After
waking, the gauge can proceed with the initialization of the battery information.
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