Issue link: https://resources.mouser.com/i/1442856
| 21 | Figure 2 Block Diagram Showing the Battery Management System in Relation to the Battery Pack Figure 3 Block Diagram of BMS IC Overview of Battery Management ICs and Transformers A typical battery monitor IC (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 pack's individual cells. 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). 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 can 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. With a rated working voltage of several hundred volts, the transformer 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. Serial Peripheral Interface (SPI) is an interface bus commonly used to send data where one device or "master" transmits a clock pulse and control bit to a series of slaves. On each clock pulse, the slave either reads a command from the master, or transmits its data on the data line if the control bit is inverse. In this way, a central battery controller IC (master) can interrogate each monitoring IC (slave) in turn and retrieve necessary voltage and temperature information from the whole pack. In addition, the transformer and integrated common mode choke filter out common mode noise from the daisy- chained network.