BQ27500 Datasheet, PDF (23/39 Pages) Texas Instruments – System-Side Impedance Track™ Fuel Gauge

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bq27500
bq27501
System-Side Impedance Track™ Fuel Gauge
SLUS785 – SEPTEMBER 2007
5.3 DETAILED DESCRIPTION OF DEDICATED PINS
5.3.1 The Operation Configuration Register
Some bq27500/1 pins are configured via the Operation Configuration data flash register, as indicated in
Table 5-3. This register is programmed/read via the methods desribed in Section 4.2.1 Accessing the Data
Flash. The register is located at subclass = 64, offset = 0.
Operation
Cfg
High Byte
Low Byte
bit7
RESCAP
–
Table 5-3. Operation Configuration Bit Definition
bit6
bit5
bit4
bit3
bit2
–
IDSELEN
–
SLEEP
PFC_CFG1 PFC_CFG0
IWAKE
RMFCC
BATL_POL BATG_POL
bit1
RSNS1
–
bit0
RSNS0
TEMPS
RESCAP = No-load rate of compensation is applied to the reserve capacity calculation. True when set. Default is 0.
PFC_CFG1/PFC_CFG0 = Pin Function Code (PFC) mode selection: PFC 0, 1, or 2 selected by 0/0, 0/1, or 1/0, respectively. Default is PFC
1 (0/1).
IWAKE/RSNS1/RSNS0 = These bits configure the current wake function (ref. Table 5-3). Default is 0/0/1.
IDSELEN = Enables cell profile selection feature. True when set. Default is 1.
SLEEP = The fuel gauge can enter sleep, if operating conditions allow. True when set. Default is 1.
RMFCC = RM is updated with the value from FCC, on valid charge termination. True when set. Default is 1.
BATL_POL = BAT_LOW pin is active-high. True when set. Default is 1.
BATG_POL = BAT_GD pin is active-low. True when cleared. Default is 0.
TEMPS = Selects external thermistor for Temperature( ) measurements. True when set. Default is 1.
5.3.2 Pin Function Code Descriptions
The bq27500/1 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 bq27500/1 measures battery temperature under discharge and
relaxation conditions. The charger does not receive any information from the bq27500/1 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 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.
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 bq27500/1 must operate in conjunction with other electronics in a system appliance, such as chargers
and other IC’s and subcircuits that draw appreciable power. After a battery is inserted into the system, this
electronics must be disabled, 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
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FUNCTIONAL DESCRIPTION
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