BQ27505 Datasheet, PDF (26/42 Pages) Texas Instruments – System-Side Impedance Track™ Fuel Gauge

bq27505
Not Recommended for New Designs
SLUS884 – FEBRUARY 2009
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5.2.8 Qmax 0 and Qmax 1
Generically called Qmax, these dynamic variables contain the respective maximum chemical capacity of
the active cell profiles, and are 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 very low rate of discharge,
such as the C/20 rate. For high accuracy, this value is periodically updated by the bq27505 during
operation. Based on the battery cell capacity information, the initial value of chemical capacity should be
entered in the Qmax n field for each default cell profile. The Impedance Track™ algorithm updates these
values and maintains them the associated actual cell profiles.
5.2.9 Update Status 0 and Update Status 1
Bit 0 (0x01) of the Update Status n registers indicates that the bq27505 has learned new Qmax
parameters and is accurate. The remaining bits are reserved. Bits 0 is user-configurable; however, it is
also a status flag that can be set by the bq27505. 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). Bit 0 is updated as needed by the bq27505.
5.2.10 Avg I Last Run
The bq27505 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 not be
modified. It is only updated by the bq27505 when required.
5.2.11 Avg P Last Run
The bq27505 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 bq27505 continuously multiplies instantaneous current times Voltage( ) to get power. It then
logs this data to derive the average power. This register should not be modified. It is only updated by the
bq27505 when required.
5.2.12 Delta Voltage
The bq27505 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.
5.2.13 Default Ra and Ra Tables
These tables contain encoded data and, with the exception of the Default Ra Tables, are automatically
updated during device operation. No user changes should be made except for reading/writing the values
from a pre-learned pack (part of the process for creating golden image files).
5.3 DETAILED PIN DESCRIPTION
5.3.1 The Operation Configuration Register
Some bq27505 pins are configured via the Operation Configuration data flash register, as indicated in
Table 5-3. This register is programmed/read via the methods described in Section 4.2.1, Accessing the
Data Flash. The register is located at subclass = 64, offset = 0.
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FUNCTIONAL DESCRIPTION
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