SLUUCO9A April 2023 – November 2023 BQ28Z620
The BQ28Z620 device implements an updated version of the battery state-of-health (SOH), which is reported by the StateofHealth() command. When calculating SOH, calculate DOD with the SOH Charge Voltage and SOH Taper Current, based on the battery cell specification. It may impact SOH accuracy if using the actual application settings.
In the BQ28Z610 firmware, the StateofHealth() is calculated using a special 25°C version of FullChargeCapacity as a fraction of Design Capacity. However, the calculation included some parameters that updated during operation based on the loading and use of the battery, separate from the battery status itself. This could lead to varying calculations of state-of-health for the same battery, depending on how the battery is used in the system. The updated version of StateofHealth() in the BQ28Z620 firmware addresses this by calculating a special SOH Full Charge Capacity, with the initial ambient temperature fixed at 25°C, using a current load specified by SOH Load Rate, and using the thermal model parameters, SOH Temp a and SOH Temp k.
The SOH Load Rate can be set to the typical current of the application, and it is specified in units of hour-rate (that is, Design Capacity / SOH Load Rate will be the current used for the SOH simulation). The SOH Temp a and SOH Temp k can be set to expected values for the system during operation. These data flash settings are used only for the StateofHealth() calculation. This SOH Full Charge Capacity is updated whenever ASOC and RSOC are updated. Because this implementation removes the variation of load current, temperature, and learned parameters, it is a better representation of the battery's state-of-health. The SOH Full Charge Capacity is available on the MAC command FCC_SOH().