The BQ28Z620 provides several Impedance Track configuration options to fine-tune the gauging performance. These configurations can be turned on or off through the corresponding flags in Settings: IT Gauging Configuration.

[LOCK0]: After a discharge event, cell voltage will usually recover to a slightly higher voltage during RELAX state. A new OCV reading during this time can result in a slightly higher state-of-charge. This flag provides an option to keep RemainingCapacity() and RelativeStateOfCharge() jumping back during relaxation after 0% and FD are reached during discharge.

[RSOC_HOLD]: An IT simulation will run at the onset of discharge. If charge terminates at a low temperature and discharge occurs at a higher temperature, the difference in temperature could cause a small rise of RSOC for a short period of time at the beginning of discharge. This flag option prevents RSOC rises during discharge. RSOC will be held until the calculated value falls below the actual state.

[RSOCL]: When set will be held to 99% until charge termination is detected.

[RFACTSTEP]: The gauge keeps track of an Ra factor of the old (old Ra)/(new Ra) during the Ra update. This factor is used for Ra scaling. It is limited to 3 max. During an Ra update, if (old Ra)/(new Ra) > 3, the gauge can take on two different actions based on the setting of this flag.

If the flag is set to 1 (default), the gauge allows Ra to update once using the max factor of 3, then disables the Ra update. If this flag is set to 0, the gauge will not update Ra and also disables the Ra update. It is recommended to keep the default setting.

[OCVFR]: An OCV reading is taken when a dV/dt condition is met. This is not the case if charging stops within the flat voltage region. The change of cell voltage in this region is very small; therefore, a same voltage error can correspond to a larger DOD error. By default, this flag is set. The device will take a 48-hour wait before taking an OCV reading if charging stops below the FlatVoltMax (max flat region voltage). The FlatVoltMax is different with different chemistry. A short discharge will not cancel this 48-hour wait. The 48-hour wait will only be cleared if charging stops above the FlatVoltMax level. Setting this flag to 0 will remove the 48-hour wait requirement, and OCV will be taken whenever the dV/dt condition is met. Removing the 48-hour requirement can be useful sometimes to reduce test time during evaluation.

[RSOC_CONV]: This function is also called fast scaling. It is an option to address the convergence of RSOC to 0% at a low temperature and a very high rate of discharge. Under such conditions, it is possible to have a drop of RSOC to 0%, especially if the termination voltage is reached at the DOD region with a higher Ra grid interval. To account for the error caused by the high granularity of the impedance grid interval, the [RSOC_CONV], when enabled, applies a scale factor to impedance, allowing more frequent impedance data updates used for RemCap simulation leading up to 0% RSOC.

[Fast_QMax_LRN] and [Fast_QMax_FLD]: The first flag enables fast QMax during the learning cycle when Update Status = 06. The second flag enables fast QMax in the field when Update Status ≥ 06.

If [RSOC_CONV] is enabled, it is recommended to start this function around the knee region of the discharge curve. This is usually around 10% of RSOC or around 3.3 V–3.5 V. This function checks for cell voltage and RSOC status and starts the function when either condition is met. The RSOC and cell voltage setting can be configured through Fast Scale Start SOC or Term Voltage.

If [FF_NEAR_EDV]: Fast Filter Near EDV. If this flag is set, the gauge applies an alternative filter, Near EDV Ra Param Filter, for an Ra update in the fast scaling region (starting around 105 RSOC). This flag should be kept to 1 as a default. When this flag is 0, the gauge uses the regular Ra filter, Resistance Parameter Filter. Both DF filters should not be changed from the default value.

[SMOOTH]: A change in temperature or current rate can cause a significant change in Remaining Capacity (RemCap), and therefore results in a jump or drop in the Relative State-of-Charge (RSOC). This function provides an option to prevent an RSOC jump or drop during charge and discharge.

If a jump or drop of RSOC occurs, the device examines the amount of the RSOC jump or drop versus the expected end point (that is, the charge termination for the charging condition or the EDV for the discharge condition) and automatically smooths the change of RSOC, and always converges with the filtered (or smoothed) value to the actual charge termination or EDV point. The actual and filtered values are always available. The [SMOOTH] flag selects either the actual or filtered values as a returned SBS command.

[RELAX_JUMP_OK]: If set to 1, this flag enables the RSOC to jump during RELAX mode. Otherwise, RSOC holds constant during RELAX mode and any RSOC jump will be passed into the onset of the charge or discharge phase.

[SYNC_AT_OCV]: If set to 1, the filtered values are synchronized to the unfiltered values when an OCV is taken.

[CELL_TERM]: This flag provides an option to calculate discharge termination based on cell voltage instead of pack voltage when this bit set, . If the minimum cell voltage reaches Term Min Cell V, RemainingCapacity() will be forced to 0 mAh.

[CSYNC]: This flag, if set to 1, synchronizes FullChargeCapacity() at valid charge termination.

[CCT]: This flag provides an option to use FullChargeCapacity() (when [CCT] = 1) or DesignCapacity() (when [CCT] = 0) for cycle count threshold calculation. The minimum cycle count threshold is always 10% of Design capacity even if FullChargeCapacity() is selected for cycle count threshold calculation. This helps to avoid any erroneous cycle count increment caused by an extremely low FullChargeCapacity().