BQ27541-V200_1007 Datasheet, PDF (25/43 Pages) Texas Instruments – Single Cell Li-Ion Battery Fuel Gauge for Battery Pack Integration

bq27541-V200
www.ti.com
SLUSA11 – FEBRUARY 2010
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
Bit 0 (0x01) of the Update Status register indicates that the bq27541 has learned new Qmax parameters and is
accurate. The remaining bits are reserved. Bits 0 is a status bit set by the bq27541. Bit 0 should never be
modified except when creating a golden image file as explained in the application note Preparing Optimized
Default Flash Constants for specific Battery Types (SLUA334.pdf). Bit 0 is updated as needed by the bq27541.
Avg I Last Run
The bq27500 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.
Max DeltaV, Min DeltaV
Maximal / Minimal value allowed for delta V, which will be subtracted from simulated voltage during remaining
capacity simulation.
Qmax Max Delta %
Maximal change of Qmax during one update, as percentage to Design Capacity. If the gauges attempts to
change Qmax exceeds this limit, changed value will be capped to old value ± DesignCapacity*QmaxMaxDelta /
100
Copyright © 2010, Texas Instruments Incorporated
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