BQ27500 Datasheet, PDF (21/39 Pages) Texas Instruments – System-Side Impedance Track™ Fuel Gauge

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bq27500
bq27501
System-Side Impedance Track™ Fuel Gauge
SLUS785 – SEPTEMBER 2007
5.2 IMPEDANCE TRACK™ VARIABLES
The bq27500/1 has several data flash variables that permit the user to customize the Impedance Track™
algorithm for optimized performance. These variables are dependent upon the power characteristics of the
application as well as the cell itself.
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.
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 =14s)
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( ). This gives a completely user configurable method.
If ILoad 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=14s) 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( ) mW. This gives a completely user configurable method.
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.
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.
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FUNCTIONAL DESCRIPTION
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