Datasheet

bq27541-G1
SLUSAL6C –NOVEMBER 2011–REVISED OCTOBER 2012 www.ti.com
Chg Current Threshold
This register is used as a threshold by many functions in the bq27541-G1 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-G1 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-G1 attempts to take accurate OCV readings. An
additional requirement of dV/dt < 1 µV/sec is required for the bq27541-G1 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.
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 low rate of discharge, such as C/20 rate. For high accuracy, this value is periodically updated by the bq27541-
G1 during operation. Based on the battery cell capacity information, the initial value of chemical capacity should
be entered in Qmax field. The Impedance Track™ algorithm will update this value and maintain it in the Pack
profile.
Update Status
The Update Status register indicates the status of the Impedance Track algorithm.
Table 12. Update Status Definitions
UPDATE STATUS STATUS
Qmax and Ra data are learned, but Impedance Track™ is not enabled. This should be the standard setting for a
0x02
golden image.
0x04 Impedance Track™ is enabled but Qmax and Ra data are not learned.
0x05 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
0x06
operation setting for end equipment.
This register should only be updated by the bq27541-G1 during a learning cycle or when IT_ENABLE
subcommand is received. Refer to the application note How to Generate Golden Image for Single-Cell
Impedance Track™Device (SLUA544) for learning cycle details.
Avg I Last Run
The bq27541-G1 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 bq27541-G1 when required.
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