BQ27520-G2 Datasheet, PDF (29/47 Pages) Texas Instruments – System-Side Impedance Track™ Fuel Gauge With Integrated LDO

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bq27520-G2
SLUSAB7A – MARCH 2011 – REVISED AUGUST 2011
5.3.2 Pin Function Code Descriptions
The bq27520-G2 has three possible pin-function variations that can be selected in accordance with the
circuit architecture of the end application. Each variation has been assigned a pin function code, or PFC.
When the PFC is set to 0, only the bq27520-G2 measures battery temperature under discharge and
relaxation conditions. The charger does not receive any information from the bq27520-G2 about the
temperature readings, and therefore operates open-loop with respect to battery temperature.
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 bq27520-G2 must be queried by the system in order to determine the battery
temperature. At that time, the bq27520-G2 samples the temperature. This saves battery energy when
operating from battery, as periodic temperature updates are avoided during charging mode. Note: Due to
thermistor sharing limitations, temperature data is not available during battery charging with PFC = 2.
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 bq27520-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 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.
Copyright © 2011, Texas Instruments Incorporated
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FUNCTIONAL DESCRIPTION
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