BQ27500_08 Datasheet, PDF (21/39 Pages) Texas Instruments – System-Side Impedance Track™ Fuel Gauge

www.ti.com
bq27500
bq27501
System-Side Impedance Track™ Fuel Gauge
SLUS785D – SEPTEMBER 2007 – REVISED APRIL 2008
5.2.1 Load Mode
Load Mode is used to select either the constant-current or constant-power model for the Impedance
Track™ algorithm as used in Load Select (see Load Select). When Load Mode is 0, the Constant
Current model is used (default). When 1, the Constant Power model is used. The [LDMD] bit of
CONTROL_STATUS reflects the status of Load Mode.
5.2.2 Load Select
Load Select defines the type of power or current model to be used to compute load-compensated
capacity in the Impedance Track™ algorithm. If Load Mode = 0 (Constant-Current) then the options
presented in Table 5-1 are available.
LoadSelect Value
0
1(default)
2
3
4
5
6
Table 5-1. Constant-Current Model Used When Load Mode = 0
Current Model Used
Average discharge current from previous cycle: There is an internal register that records the average discharge
current through each entire discharge cycle. The previous average is stored in this register.
Present average discharge current: This is the average discharge current from the beginning of this discharge cycle
until present time.
Average current: based on AverageCurrent( )
Current: based off of a low-pass-filtered version of AverageCurrent( ) (τ =14 s)
Design capacity / 5: C Rate based off of Design Capacity /5 or a C/5 rate in mA.
AtRate (mA): Use whatever current is in AtRate( )
User_Rate-mA: Use the value in User_Rate-mA. This mode provides a completely user-configurable method.
If Load Mode = 1 (Constant Power) then the following options shown in Table 5-2 are available.
LoadSelect Value
0
1(default)
2
3
4
5
6
Table 5-2. Constant-Power Model Used When Load Mode = 1
Power Model Used
Average discharge power from previous cycle: There is an internal register that records the average discharge power
through each entire discharge cycle. The previous average is stored in this register.
Present average discharge power: This is the average discharge power from the beginning of this discharge cycle
until present time.
Average current × voltage: based off the AverageCurrent( ) and Voltage( ).
Current × voltage: based off of a low-pass-filtered version of AverageCurrent( ) (τ=14 s) and Voltage( )
Design energy / 5: C Rate based off of Design Energy /5 or a C/5 rate in mA.
AtRate (10 mW): Use whatever value is in AtRate( ).
User_Rate-10mW: Use the value in User_Rate-10mW. This mode provides a completely user-configurable method.
5.2.3 Reserve Cap-mAh
Reserve Cap-mAh determines how much actual remaining capacity exists after reaching 0
RemainingCapacity( ), before Terminate Voltage is reached. A no-load rate of compensation is applied
to this reserve.
5.2.4 Reserve Cap-mWh
Reserve Cap-mWh determines how much actual remaining capacity exists after reaching 0
AvailableEnergy( ), before Terminate Voltage is reached. A no-load rate of compensation is applied to
this reserve capacity.
5.2.5 Dsg Current Threshold
This register is used as a threshold by many functions in the bq27500/1 to determine if actual discharge
current is flowing into or out of the cell. The default for this register is 100 mA, which should be sufficient
for most applications. This threshold should be set low enough to be below any normal application load
current but high enough to prevent noise or drift from affecting the measurement.
Submit Documentation Feedback
FUNCTIONAL DESCRIPTION
21