A new feature is added to BQ78350-R3 to activate the cell balancing operation when the device is at REST. Writing to the 0xB1 CB_REST_Enable() command enables or disables this feature. The Balancing Configuration[CB_REST] DF bits sets the default enable/disable configuration of this feature upon device POR. If this feature is enabled when [CB] = 1, and the voltage level of the lowest cell is above the voltage level programmed in the Cell Balance Threshold register, cell balancing operation will be activated when the device enters REST mode. In the same way as normal cell balancing during CHARGE mode, only the non-adjacent cells will be balanced at the same time during REST mode.

When cell balancing operation is activated in REST mode, the dynamic cell balance threhold will automatically be set to the voltage level which is Cell Balance Min above the lowest cell voltage, without Cell Balance Window adjustment, and continue to decrease as the cell voltages decrease over time due to leakag while remaining above the Cell Balance Threshold voltage level. This ensures the cell balancing operation continues to operate in REST if the maximum difference in cell voltages exceeds the value programmed in Cell Balance Min, without over discharging the batteries in case the voltage level programmed in Cell Balance Threshold is significantly lower than the lowest cell voltage. #SLUU319IMG6701 shows how the cell balancing operates in REST mode when this feature is activated.

Cell balancing at REST will complete when the maximum difference in cell voltages is less than the value programmed in Cell Balance Min. Upon completion while the lowest cell voltage is still above the voltage level programmed in Cell Balance Threshold, if a fast leaking cell causes the maximum difference in cell voltages to widen again beyond Cell Balance Min, the cell balancing at REST will re-activate. When the device exits REST mode or when any of the cell voltage falls below the programmed value of Cell Balance Threshold, cell balancing at REST will stop even before the balancing operation is completed.