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5.3.5 Battery Detection Using the BI/TOUT Pin
bq27500
bq27501
System-Side Impedance Track™ Fuel Gauge
SLUS785 – SEPTEMBER 2007
for the fuel gauge to take an accurate OCV reading. To disable these functions, the BAT_GD pin is merelyset high (floating output pulled high). Once an OCV reading has be made, the 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 configurationneed to be changed.
The flowchart of Figure 5-1 details how the BAT_GD pin functions in the context of battery insertion andremoval, as well as NORMAL vs SLEEP modes.
In PFC 1, the BAT_GD pin is also used to disable battery charging when the bq27500/1 reads batterytemperatures outside the range defined by [Charge Inhibit Temp Low, Charge Inhibit Temp High]. TheBAT_GD line is returned to low once temperature falls within the range [Charge Inhibit Temp Low +Temp Hys, Charge Inhibit Temp High – Temp Hys].
During power-up or HIBERNATE activities, or any other activity where the bq27500/1 needs to determinewhether a battery is connected or not, the fuel gauge applies a test for battery presence. First, theBI/TOUT pin is put into high-Z status. The weak 1.8M Ωpull-up resistor will keep the pin high while nobattery is present. When a battery is inserted (or is already inserted) into the system device, the BI/TOUTpin will be pulled low. This state is detected by the fuel gauge, which polls this pin every second when thegauge has power. A battery disconnected status is assumed when the bq27500/1 reads a thermistorvoltage that is near 2.5V.
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