BQ27510_08 Datasheet, PDF (21/36 Pages) Texas Instruments – System-Side Impedance Track™ Fuel Gauge With Direct Battery Connection

bq27510
www.ti.com.......................................................................................................................................................... SLUS816A – MARCH 2008 – REVISED JUNE 2008
LoadSelect
Value
4
5
6
Table 8. Constant-Current Model Used When Load Mode = 0 (continued)
Current Model Used
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 Load Mode = 1 (Constant Power) then the following options are available:
LoadSelect
Value
0(default)
1
2
3
4
5
6
Table 9. Constant-Current Model Used When Load Mode = 1
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 × 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 current is in AtRate( )
User_Rate-10 mW: 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.
Dsg Current Threshold
This register is used as a threshold by many functions in the bq27510 to determine if actual discharge current is
flowing into or out of the cell. The 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 bq27510 to determine if actual charge current is
flowing into or out of the cell. The 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 bq27510 enters
relaxation mode from a current flowing mode in either the charge direction or the discharge direction. The value
of Quit Current should be above the standby current of the system.
The following criteria must be met to enter relaxation mode
| AverageCurrent( ) | < | Quit Current | for Dsg Relax Time (if in CHG mode) or Chg Relax Time (if in DSG
mode).
After about 30 minutes in relaxation mode, the bq27510 attempts to take accurate OCV readings. An additional
requirement of dV/dt 4 µV/sec is required for the bq27510 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 to and
that the current is not be higher than C/20 when attempting to go into relaxation mode.
Copyright © 2008, Texas Instruments Incorporated
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