BQ27541-V200_17 Datasheet, PDF (25/46 Pages) Texas Instruments – Single Cell Li-Ion Battery Fuel Gauge for Battery Pack Integration

Not Recommended for New Designs
bq27541-V200
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SLUSA11B – FEBRUARY 2010 – REVISED SEPTEMBER 2013
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
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.
UPDATE STATUS
0x02
0x04
0x05
0x06
Table 11. 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 bq27541 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 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 when required.
Avg P Last Run
The bq27541 logs the power averaged from the beginning to the end of each discharge cycle. It stores this
average power from the previous discharge cycle in this register. To get a correct average power reading the
bq27541 continuously multiplies instantaneous current times Voltage( ) to get power. It then logs this data to
derive the average power. This register should never need to be modified. It is only updated by the bq27541
when required.
Delta Voltage
The bq27541 stores the maximum difference of Voltage( ) during short load spikes and normal load, so the
Impedance Track™ algorithm can calculate remaining capacity for pulsed loads. It is not recommended to
change this value.
Ra Tables and Ra Filtering Related Parameters
These tables contain encoded data and are automatically updated during device operation. In bq27541, during
the update of Ra values a filtering process is performed to eliminate unexpected fluctuations in the updated Ra
values. The DF parameters RaFilter, RaMaxDelta, MaxResfactor and MinResfactor control the Filtering process
of Ra values. RaMaxDelta Limits the change in Ra values to an absolute magnitude. MinResFactor and
MaxResFactor parameters are cumulative filters which limit the change in Ra values to a scale on a per
discharge cycle basis. These values are Data Flash configurable. No further user changes should be made to Ra
values except for reading/writing the values from a prelearned pack (part of the process for creating golden
image files).
MaxScaleBackGrid
MaxScaleBackGrid parameter limits the resistance grid point after which back scaling will not be performed. This
variable ensures that the resistance values in the lower resistance grid points remain accurate while the battery
is at a higher DoD state.
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