BQ27541-V200_17 Datasheet, PDF (24/46 Pages) Texas Instruments – Single Cell Li-Ion Battery Fuel Gauge for Battery Pack Integration

bq27541-V200
Not Recommended for New Designs
SLUSA11B – FEBRUARY 2010 – REVISED SEPTEMBER 2013
If Load Mode = 1 (Constant Power) then the following options are available:
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LoadSelect Value
0 (default)
1
2
3
4
5
6
Table 10. 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( ). 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 loaded rate or no-load rate of compensation
can be selected for Reserve Cap by setting [RESCAP] bit in Pack Configuration Register.
Reserve Cap-mWh
Reserve Cap-mWh determines how much actual remaining capacity exists after reaching 0 AvailableEnergy( ),
before Terminate Voltage is reached. A loaded rate or no-load rate of compensation can be selected for
Reserve Cap by setting [RESCAP] bit in Pack Configuration Register.
Dsg Current Threshold
This register is used as a threshold by many functions in the bq27541 to determine if actual discharge current is
flowing into or out of the cell. The default for this register 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.
Chg Current Threshold
This register is used as a threshold by many functions in the bq27541 to determine if actual charge current is
flowing into or out of the cell. The default for this register should be sufficient for most applications. This threshold
should be set low enough to be below any normal charge current but high enough to prevent noise or drift from
affecting the measurement.
Quit Current, Dsg Relax Time, Chg Relax Time, and Quit Relax Time
The Quit Current is used as part of the Impedance Track™ algorithm to determine when the bq27541 enters
relaxation mode from a current flowing mode in either the charge direction or the discharge direction. The value
of Quit Current is set to a default value that should be above the standby current of the system.
Either of the following criteria must be met to enter relaxation mode:
1. | AverageCurrent( ) | < | Quit Current | for Dsg Relax Time.
2. | AverageCurrent( ) | < | Quit Current | for Chg Relax Time.
After about 6 minutes in relaxation mode, the bq27541 attempts to take accurate OCV readings. An additional
requirement of dV/dt < 4 µV/sec is required for the bq27541 to perform Qmax updates. These updates are used
in the Impedance Track™ algorithms. It is critical that the battery voltage be relaxed during OCV readings and
that the current is not higher than C/20 when attempting to go into relaxation mode.
Quit Relax Time specifies the minimum time required for AverageCurrent( ) to remain above the QuitCurrent
threshold before exiting relaxation mode.
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