BQ27620-G1 Datasheet, PDF (28/45 Pages) Texas Instruments – System-Side Impedance Track™ Fuel Gauge

bq27620-G1
SLUSAE3 – OCTOBER 2012
www.ti.com
5.2.5 Dsg Current Threshold Rate
This register is used as a threshold by many functions in the bq27620-G1 to determine if actual discharge
current is flowing into or out of the cell. The default for this register is in Section 4.6, which should be
sufficient for most applications. This threshold should be set low enough to be below any normal
application load current but high enough to prevent noise or drift from affecting the measurement.
5.2.6 Chg Current Threshold Rate
This register is used as a threshold by many functions in the bq27620-G1 to determine if actual charge
current is flowing into or out of the cell. The default for this register is in Section 4.6, which 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.
5.2.7 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 bq27620-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 in Section 4.6 and should be above the
standby current of the system.
Either of the following criteria must be met to enter relaxation mode:
• | EffectiveCurrent( ) | < | Quit Current | for Dsg Relax Time
• | EffectiveCurrent( ) | < | Quit Current | for Chg Relax Time
After about 5 minutes in relaxation mode, the bq27620-G1 attempts to take accurate OCV readings. An
additional requirement of dV/dt < 1 μV/s is required for the bq27620-G1 to perform optimization cycle.
These updates are used in the Impedance Track™ algorithms. It is critical that the battery voltage be
relaxed during OCV readings to and that the current is not be higher than C/20 when attempting to go into
relaxation mode.
Quit Relax Time specifies the minimum time required for EffectiveCurrent( ) to remain above the
QuitCurrent threshold before exiting relaxation mode.
5.2.8 Delta Voltage
The bq27620-G1 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.
5.2.9 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. Arbitrations happen on pack insert and based on a Ra measurement. 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).
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FUNCTIONAL DESCRIPTION
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