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5.3 DETAILED DESCRIPTION OF DEDICATED PINS
5.3.1 The Operation Configuration Register
5.3.2 Pin Function Code Descriptions
5.3.3 BAT_LOW Pin
5.3.4 Power Path Control with the BAT_GD Pin
bq27500
bq27501System-Side Impedance Track™ Fuel Gauge
SLUS785 – SEPTEMBER 2007
Some bq27500/1 pins are configured via the Operation Configuration data flash register, as indicated inTable 5-3 . This register is programmed/read via the methods desribed in Section 4.2.1 Accessing the DataFlash. The register is located at subclass = 64, offset = 0.
Table 5-3. Operation Configuration Bit Definition
Operation bit7 bit6 bit5 bit4 bit3 bit2 bit1 bit0Cfg
High Byte RESCAP – – PFC_CFG1 PFC_CFG0 IWAKE RSNS1 RSNS0
Low Byte – IDSELEN SLEEP RMFCC BATL_POL BATG_POL – 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 PFC1 (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.
The bq27500/1 has three possible pin-function variations that can be selected in accordance with thecircuit 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 andrelaxation conditions. The charger does not receive any information from the bq27500/1 about thetemperature 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 chargingtemperature falls outside of the preset range defined in data flash,a charger can be disabled via theBAT_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 thecharger. The charger has full usage of the thermistor during battery charging, while the fuel gauge usesthe thermistor exclusively during discharge and battery relaxation.
The PFC is specified in Operation Configuration [PFC_CFG1, PFC_CFG0]. The default is PFC = 1.
The BAT_LOW pin provides a system processor with an electrical indicator of battery status. The signalingon the BAT_LOW pin follows the status of the [SOC1] bit in the Flags( ) register. Note that the polarity ofthe BAT_LOW pin can be inverted via the [BATL_POL] bit of Operation Configuration.
The bq27500/1 must operate in conjunction with other electronics in a system appliance, such as chargersand other IC’s and subcircuits that draw appreciable power. After a battery is inserted into the system, thiselectronics must be disabled, so that an accurate OCV can be read. The OCV is used for helpingdetermine 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 ofthe battery takes place and that any discharge is limited to less than C/20—these conditions are sufficient
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