Battery cell balancing and monitoring

When designing a BMS, the designer often starts with the cell monitoring and balancing (CMB) device. The CMB device is also known as the BMS IC or AnalogFront End (AFE). Often located on a Cell Management Controller (CMC) unit, the CMB’s function is to measure the voltages and temperatures for cells and communicate this information to the main controller. Additionally, the CMB can undertake diagnostics of cells and their surrounding (for example, detecting connection failures in the circuit surrounding a cell such as open or short circuits). The values monitored by the CMB are then used to:

The CMB device is also responsible for balancing the cells. Cell imbalance comes from the fact that high voltage batteries are built out of many single cells in series, which inevitably have production variances, for example in cell characteristics or the heterogeneous thermal spreads in the final pack.

Additionally, to achieve extreme low-power dedicated housekeeping functions such as periodically scheduled cell measurements and state analysis required for functional safety can be performed by the CMB independently from the master controller of the BMS. Safety features for signaling over-/under-voltage, thermal stress, etc. including emergency alarms are triggered autonomously.