SLUUBT5C November 2018 – June 2021 BQ40Z80
The BQ40Z80 implements a new state-of-health (SOH) function. Previously, the SOH of a battery was typically represented by the actual runtime FullChargeCapacity/Design Capacity (or FCC/DC). Using the runtime FCC, however, was not a very good representation for the state-of-health because the runtime FCC reflects the usable capacity under load. A high current load reduces the runtime FCC. If using just the FCC/DC calculation for SOH, the SOH under high load will be worse than the SOH under typical load. However, a smaller usable capacity at high load does not mean the SOH of a battery is degraded. This is the same when FCC is reduced at a lower temperature.
The BQ40Z80 implementation of state-of-health addresses these issues. It provides the SOH of the battery through an SBS command, SOH(). The SOH() is calculated using the FCC simulated at 25°C with current specified by SOH Load Rate. The SOH Load Rate can be set to the typical current of the application, and it is specified in hour-rate (that is, Design Capacity/SOH Load Rate will be the current used for the SOH simulation). This data flash setting is used for SOH() calculation only. This SOH FCC is updated at the same time ASOC and RSOC are updated. Since this implementation removes the variation of current or temperature, it is a better representation of a battery’s state-of-health. The SOH FCC is available on MAC StateofHealth().