BQ34Z100 Datasheet, PDF (18/50 Pages) Texas Instruments – Wide Range Fuel Gauge with Impedance Track™ Technology

bq34z100
SLUSAU1 – MAY 2012
www.ti.com
Dsg Current Threshold
This register is used as a threshold by many functions in the bq34z100 to determine if actual discharge 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 application load current but high enough to prevent noise or
drift from affecting the measurement.
Chg Current Threshold
This register is used as a threshold by many functions in the bq34z100 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 bq34z100 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 host 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 bq34z100 attempts to take accurate OCV readings. An
additional requirement of dV/dt < 4 μV/s is required for the bq34z100 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 to 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 Cell 0 contains the maximum chemical capacity of the cell and is determined by comparing states of
charge before and after applying the load with the amount of charge passed. It also corresponds to capacity at
low rate of discharge such as C/20 rate. For high accuracy, this value is periodically updated by the bq34z100
during operation.
Based on the battery cell capacity information, the initial value of chemical capacity should be entered in the
Qmax Cell 0 data flash parameter. The Impedance Track algorithm will update this value and maintain it
internally in the gauge.
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 File.
Impedance Track is enabled but Qmax and Ra data are not yet 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.
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