Issue link: https://resources.mouser.com/i/1442820
| 17 | Overview of Battery Management ICs and Transformers Figure 3: Block Diagram of BMS IC A typical battery monitor IC (shown in Figure 3) measures cell voltage and pack temperature and performs cell balancing. In some models, there is also a current sense input port for shunt-based current measurement. Including this feature makes sense in 48V systems that use a limited number of battery cells and do not experience hazardous voltage levels, and, hence, monitoring ICs. Conversely, it does not add a lot of value to integrate a current sense function into an IC for high voltage battery packs. These packs require only one current sensing chip and several monitoring ICs to monitor the individual cells in the pack. For instance, the 2011 Nissan ® Leaf ® has a working voltage of 360V and energy of 24kWh (NMC technology). The structure of the pack is 96S2P (192 cells). Or, a simpler way to put it: if each monitoring IC can check 10 cells, then at least 20 monitoring ICs will be needed. Another consideration in high voltage battery packs is that the BMS IC module or board must be located on top of the shunt resistor, which may pose a mechanical design challenge. BMS High Voltage Communications The BMS typically has two ports for isolated communications, allowing battery monitoring modules to be daisy-chained throughout the battery pack. The source and sink currents of the serial port drivers are balanced, enabling the IC to drive a transformer without saturating it. The transformer, with a rated working voltage of several hundred volts, provides the necessary protection of the communications line from any hazardous voltage coming from the battery pack. Furthermore, the drivers on the IC encode a four-line serial peripheral protocol into the differential signal needed for isolated communication from board to board. Figure 2: Block Diagram Showing the Battery Management System in Relation to the Battery Pack