BQ27505-J4 Datasheet, PDF (23/38 Pages) Texas Instruments – System-Side Impedance Track™ Fuel Gauge

www.ti.com
bq27505-J4
SLVSA40 – DECEMBER 2009
5.2 IMPEDANCE TRACK™ VARIABLES
The bq27505-J4 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.
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(). 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:
Table 5-2. Constant-Power Model Used When Load Mode = 1
LoadSelect Value
Power Model Used
0(default)
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.
1
Present average discharge power: This is the average discharge power from the beginning of this discharge cycle until
present time.
2
Average current × voltage: based off the AverageCurrent( ) and Voltage( ).
3
Current × voltage: based off of a low-pass-filtered version of AverageCurrent( ) (τ=14 s) and Voltage( )
4
Design energy / 5: C Rate based off of Design Energy /5 or a C/5 rate in mA.
5
AtRate (10 mW): Use whatever value is in AtRate( ).
6
User_Rate-10mW: Use the value in User_Rate() mW. 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.
Copyright © 2009, Texas Instruments Incorporated
Submit Documentation Feedback
FUNCTIONAL DESCRIPTION
23