BQ27510-G1 Datasheet, PDF(24/39 Page) Texas Instruments – System-Side Impedance Track™ Fuel Gauge With Direct Battery Connection

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bq27510-G1

SLUS927 â APRIL 2009 ..................................................................................................................................................................................................... www.ti.com

Battery Detection using the BI/TOUT Pin

During power-up or hibernate activities, or any other activity where the bq27510 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 1.8Mâ¦ 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 reads a thermistor voltage that is near 2.5V.

TEMPERATURE MEASUREMENT

The bq27510 measures battery temperature via its TS input, in order to supply battery temperature status

information to the fuel gauging algorithm and charger-control sections of the gauge. Alternatively, it can also

measure internal temperature via its on-chip temperature sensor, but only if the [TEMPS] bit of Operation

Configuration register is cleared.

Regardless of which sensor is used for measurement, a system processor can request the current battery

temperature by calling the Temperature( ) function (see Section Standard Data Commands, for specific

information).

The external temperature measurement circuit must use a 103AT-type thermistor. Additional circuit information

for connecting this thermistor to the bq27510 is shown in Section Reference Schematic.

OVER-TEMPERATURE INDICATION

Over-Temperature: Charge

If during charging, Temperature( ) reaches the threshold of OT Chg for a period of OT Chg Time and

AverageCurrent( ) > Chg Current Threshold, then the [OTC] bit of Flags( ) is set. When Temperature( ) falls to

OT Chg Recovery, the [OTC] of Flags( ) is reset.

If OT Chg Time = 0 then feature is completely disabled.

Over-Temperature: Discharge

If during discharging, Temperature( ) reaches the threshold of OT Dsg for a period of OT Dsg Time and

AverageCurrent( ) â¤ -Dsg Current Threshold, then the [OTD] bit of Flags( ) is set. When Temperature( ) falls to

OT Dsg Recovery, the [OTD] of Flags( ) is reset.

If OT Dsg Time = 0 then feature is completely disabled.

CHARGING AND CHARGE-TERMINATION INDICATORS

Detecting Charge Termination

For proper bq27510 operation, the cell charging voltage must be specified by the user. The default value for this

variable is Charging Voltage = 4200mV.

The bq27510 detects charge termination when (1) during 2 consecutive periods of Current Taper Window, the

AverageCurrent( ) is < Taper Current, (2) during the same periods, the accumulated change in capacity > Min

Taper Charge / Current Taper Window, and (3) Voltage( ) > Charging Voltage â Taper Voltage. When this

occurs, the [CHG] bit of Flags( ) is cleared. Also, if the [RMFCC] bit of Operation Configuration is set, and

RemainingCapacity( ) is set equal to FullChargeCapacity( ).

Charge Inhibit and Suspend

The bq27510 can indicate when battery temperature has fallen below or risen above predefined thresholds

Charge Inhibit Temp Low or Charge Inhibit Temp High, respectively. In this mode, the [CHG_INT] bit is set

and the BAT_GD pin is deserted to indicate this condition. The [CHG_INT] bit is cleared and the BAT_GD pin is

asserted once the battery temperature returns to the range [Charge Inhibit Temp Low + Temp Hys, Charge

Inhibit Temp High â Temp Hys].

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