BQ28Z560-R1_14 Datasheet, PDF (34/61 Pages) Texas Instruments – Single Cell Li-Ion Battery Gas Gauge

bq28z560-R1
Not Recommended For New Designs
SLUSBD3 – APRIL 2013
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Chg Current Threshold
This register is used as a threshold by many functions in the bq28z560-R1 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 bq28z560-R1 enters
RELAX 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 RELAX mode:
1. | AverageCurrent() | < | Quit Current | for Dsg Relax Time.
2. | AverageCurrent() | < | Quit Current | for Chg Relax Time.
After about 6 minutes in RELAX mode, the bq28z560-R1 attempts to take accurate OCV readings. An additional
requirement of dV/dt < 4 µV/s is required for the bq28z560-R1 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 RELAX mode.
Quit Relax Time specifies the minimum time required for AverageCurrent() to remain above the QuitCurrent
threshold before exiting RELAX mode.
Qmax
Qmax contains the maximum chemical capacity of the active cell profiles, and is determined by comparing states
of charge before and after applying the load with the amount of charge passed. They also correspond to capacity
at a low rate of discharge, such as C/20 rate. For high accuracy, this value is periodically updated by the
bq28z560-R1 during operation. Based on the battery cell capacity information, the initial value of chemical
capacity should be entered in the Qmax field. The Impedance Track algorithm updates this value and maintains
it in the Pack profile.
Update Status
The Update Status register indicates the status of the Impedance Track algorithm.
UPDATE STATUS
0x02
0x04
0x05
0x06
Table 14. Update Status Definitions
STATUS
Qmax and Ra data are learned, but Impedance Track is not enabled. This should be the standard setting for a
golden image.
Impedance Track is enabled but Qmax and Ra data are not learned.
Impedance Track is enabled and only Qmax has been updated during a learning cycle.
Impedance Track is enabled. Qmax and Ra data are learned after a successful learning cycle. This should be the
operation setting for end equipment.
This register should only be updated by the bq28z560-R1 during a learning cycle or when IT_ENABLE()
subcommand is received. Refer to the application note How to Generate Golden Image for a Single-Cell
Impedance Track™ Device (SLUA544) for learning cycle details.
Avg I Last Run
The bq28z560-R1 logs the current averaged from the beginning to the end of each discharge cycle. It stores this
average current from the previous discharge cycle in this register. This register should never need to be
modified. It is only updated by the bq28z560-R1 when required.
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