SLUUCA6 October 2021 BQ27Z746
The Fast QMax update conditions are very similar to the QMax update conditions with the following differences:
The differences in requirements enable the Fast QMax feature to have a QMax update at the end of discharge (given one OCV reading is already available and discharge < 10% RSOC) without a longer relax time after a discharge event. The temperature, delta capacity, voltage, and offset error requirements for a QMax update are still required for the Fast QMax update.
This feature is particularly useful for reducing production QMax learning cycle time or for an application that is mostly in CHARGE or DISCHARGE state with infrequent relaxation. Setting IT Gauging Configuration[FAST_QMAX_LRN] = 1 enables Fast QMax during production learning only (that is, Update Status = 06). When setting IT Gauging Configuration[FAST_QMAX_FLD] = 1, Fast QMax is enabled when Impedance Track is enabled and Update Status = 06 or 0E.
The DOD is taken for QMax at a high state-of-charge, then during discharge when at the steep portion of the voltage curve (92–96% DOD). This enables a good estimation of DOD. This DOD estimation during discharge is used to update QMax immediately instead of first needing a rest period. The actual update to QMax occurs when the discharge stops after verifying that no conditions are present to cause the QMax update to fail. The BQ27Z746 devoce has an option to qualify DODEOC for QMax updates, which means it is possible to update QMax with no rest periods (by having a charge termination followed by a full discharge). Fast QMax can be enabled in either LEARN mode ([FAST_QMAX_LRN]) or FIELD mode ([FAST_QMAX_FLD]). The LEARN mode flag means Fast QMax is only enabled with Update Status = 06, and will be disabled when the status = 0x0E. FIELD mode means Fast QMax is enabled with Update Status = 06 and 0E.