Digital isolator Si8641 typical circuit and OBC controller system

At present, pure electric bus technology is very mature, and most car manufacturers use on-board OBC controller technology to realize power battery charging management. The OBC controller converts 220V into DC through a controllable rectifier bridge, filters it and supplies it to the high-frequency DC-DC power converter, and then filters it again to charge the pure electric vehicle power battery according to the DC required by the vehicle model and power output. In this process, the controllable rectifier bridge module design generally adopts a half-bridge topology composed of driver + MOSFET. Then the driver is not only a driving device that carries low voltage to high voltage, that is, it must have an output capability greater than 2.5A, and it must also have a 5KV isolation function to protect the subsequent MOSFET circuit.

Based on the above requirements, Silicon Labs (also known as "Silicon Technology") provides the Si8233 driver isolator, which has a maximum output current of 4A, a safe isolation voltage of 5kvrms, supports SOIC-8 and SOIC-16 packages, and supports up to 1,500 VDC Peak drive voltage. Compared with other similar products, its advantage lies in its large driving current and high cost performance.

Figure 1: Typical circuit of Si8233 driving MOSFET

The OBC controller will have 5V and 3.3V data communication at the same time. For example, the MCU may work at 3.3V, while some other ICs work at 5V. At this time, I2C, SPI, and IO need to be isolated to protect the The voltage difference causes the subsequent IC to be burned. The digital isolator Si8641 launched by Silicon Labs is recommended here. It is specially customized for SPI communication isolation. It supports three same-direction channels and one reverse channel, and the MCU of the OBC controller can be used through pins EN1 and EN2. For controlling the output of Si8641, this has the advantage of improving the EMC reliability of the OBC controller and preventing the OBC controller from crashing due to voltage differences.

Figure 2: Typical circuit of digital isolator Si8641

There are many ways to implement the functions of the on-board OBC controller, but as the core device driver Si8233 and digital isolator Si8641 have been adopted by many companies in their design solutions. It has now been successfully used by some customers in East China and passed all tests by the car factory.