BQ27510-G2 Datasheet, PDF (23/38 Pages) Texas Instruments – System-Side Impedance Track™ Fuel Gauge With Direct Battery Connection

bq27510-G2
www.ti.com
SLUS948 – AUGUST 2010
A PFC of 1 is like a PFC of 0, except the BAT_LOW/BAT_GD pin is used to signal temperature thresholds during
charge. If charging temperature falls outside of the preset range defined in data flash, a charger can be disabled
via the BAT_LOW/BAT_GD pin, until cell temperature recovers. See Charge Inhibit 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. Thus temperature is not measured during charge. Note that
removing the battery while charging will not result in BAT_DET clearing if PFC = 2.
The PFC is specified in Operation Configuration [PFC_CFG1, PFC_CFG0]. The default is PFC = 1.
BAT_LOW/BAT_GD Pin
The BAT_LOW/BAT_GD is a multiplex pin. The function is defined by [BAT_FN] as a system processor with an
electrical indicator of battery status. It the BAT_LOW function is activated, the signaling on the multiplexed pin
follows the status of the [SOC1] bit in the Flags( ) register. Note that the polarity of the pin output can be inverted
via the [BATL_POL] bit of the Operation Configuration.
The bq27510-G2 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 or 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_LOW/BAT_GD pin is merely set
high (floating output pulled high). Once an OCV reading has be made, the BAT_LOW/BAT_GD pin is pulled low,
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.
The flowchart of Figure 2 details how the BAT_LOW/BAT_GD pin functions in the context of battery insertion and
removal, as well as NORMAL vs. SLEEP modes when [BAT_FN] is set.
In PFC 1, the BAT_LOW/BAT_GD pin is also used to disable battery charging when the bq27510-G2 reads
battery temperatures outside the range defined by [Charge Inhibit Temp Low, Charge Inhibit Temp High]. The
BAT_LOW/BAT_GD line is returned to "low" once temperature falls within the range [Charge Inhibit Temp Low
+ Temp Hys, Charge Inhibit Temp High – Temp Hys].
Battery Detection using the BI/TOUT Pin
During power-up or hibernate activities, or any other activity where the bq27510-G2 needs to determine whether
a battery is connected or not, the fuel gauge applies a test for battery presence. First, the BI/TOUT pin is put into
high-Z status. The weak 1.8MΩ pull-up resistor will keep the pin high while no battery is present. When a battery
is inserted (or is already inserted) into the system device, the BI/TOUT pin will be pulled low. This state is
detected by the fuel gauge, which polls this pin every second when the gauge has power. A battery-disconnected
status is assumed when the bq27510-G2 reads a thermistor voltage that is near 2.5V.
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