BQ27505-J3 Datasheet, PDF (28/44 Pages) Texas Instruments – System-Side Impedance Track™ Fuel Gauge

bq27505-J3
Not Recommended for New Designs
SLUS986A – OCTOBER 2009 – REVISED FEBRUARY 2010
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A PFC of 1 is like a PFC of 0, except temperature is also monitored during battery charging. If charging
temperature falls outside of the preset range defined in data flash, a charger can be disabled via the
BAT_GD pin until cell temperature recovers. See Section 5.6.2, Charge Inhibit and Suspend, for additional
details.
Finally when the PFC is set to 2, the battery thermistor can be shared between the fuel gauge and the
charger. The charger has full usage of the thermistor during battery charging, while the fuel gauge uses
the thermistor exclusively during discharge and battery relaxation.
When PFC = 0 or 2, the bq27505 must be queried by the system in order to determine the battery
temperature. At that time, the bq27505 samples the temperature. This saves battery energy when
operating from battery, as periodic temperature updates are avoided during charging mode.
The PFC is specified in Operation Configuration [PFC_CFG1, PFC_CFG0]. The default is PFC = 1.
5.3.3 BAT_LOW Pin
The BAT_LOW pin provides a system processor with an electrical indicator of battery status. The signaling
on the BAT_LOW pin follows the status of the [SOC1] bit in the Flags( ) register. Note that the polarity of
the BAT_LOW pin can be inverted via the [BATL_POL] bit of Operation Configuration.
5.3.4 Power Path Control With the BAT_GD Pin
The bq27505 must operate in conjunction with other electronics in a system appliance, such as chargers
or other ICs and application circuits that draw appreciable power. After a battery is inserted into the
system, there should be no charging current or a discharging current higher than C/20, so that an accurate
OCV can be read. The OCV is used for helping determine which battery profile to use, as it constitutes
part of the battery impedance measurement
When a battery is inserted into a system, the Impedance Track™ algorithm requires that no charging of
the battery takes place and that any discharge is limited to less than C/20—these conditions are sufficient
for the fuel gauge to take an accurate OCV reading. To disable these functions, the BAT_GD pin is merely
negated from the default setting. Once an OCV reading has be made, the BAT_GD pin is asserted,
thereby enabling battery charging and regular discharge of the battery. The Operation Configuration
[BATG_POL] bit can be used to set the polarity of the battery good signal, should the default configuration
need to be changed.
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FUNCTIONAL DESCRIPTION
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