Compared with industrial applications, the isolation requirements of automobiles are higher, the complex road conditions and the noise during high-speed operation all have great interference on the system, which all lead to stricter requirements for safety in automobile applications. In actual use, defects or reliability problems may lead to costly product recalls, and may even endanger the safety of drivers and passengers.
In order to meet the increasingly stringent quality and reliability requirements, automotive system designers began to use digital isolators instead of photocouplers to provide safe isolation for hybrid electric vehicle (HEV) battery monitoring and power conversion applications. Unlike optocouplers, digital isolators are based on standard wafer CMOS semiconductor technology, which has a good reputation in automotive systems.
The distributed control strategy of new energy vehicle bus still follows the fuel vehicle mode, ECU centralized control, CAN bus node management, and errors are not allowed in this control system, because these directly affect the vehicle driving safety and the normal operation of various components. In addition to the CAN bus between nodes, the underlying data exchange between MCU and sensors uses SPI bus, PWM, SENT or analog signals, which need to be isolated to ensure accuracy and reliability.
During the development of electric vehicle electronic circuits, digital isolators can be used to transmit digital signals between high-voltage battery packs and low-voltage control system electronic components. This scheme is applicable to a variety of applications, such as high-voltage battery pack voltage monitoring, battery current measurement, motor control, etc. Especially in the application of battery management system (BMS). For the selection of digital isolation devices, the designer must consider several key performance parameters, including: device power consumption, PCB space limit, data rate/data consistency (matching between channels), and appropriate isolation and working voltage (throughout the vehicle life cycle).
For the working current required by the isolation device, there is a big difference between the digital isolator and the optical coupler. Assuming that a 1MHz SPI interface is used for battery monitoring applications, for the four digital isolation channels required by the SPI communication bus, the ME1041 of CSG Microelectronics has significant advantages in working power consumption compared with the traditional optical coupler solution.
L In BMS development, PCB area is a valuable asset, and designers must build solutions that can be applied to ultra-compact areas. The spacing requirements (generally referred to as creepage distance and clearance) of high-voltage to low-voltage interfaces are defined by various electrical standards, and the components must meet the minimum requirements specified by these standards for a given application. Two isolation solutions, digital and optical coupler, are compared to determine which one can save a lot of space for PCB.
For digital isolation solution, ME1041 adopts 16-pin SOIC-W package, with standard package size of 10.3mm x 10.3mm and total area of 106 mm2. The equivalent optocoupler solution requires four 5-pin SOIC package devices. The standard JEDEC package size is 7.0 mm x 3.6 mm, and the unit area is 25.2 mm2. Four components need to be placed on the PCB board, and the spacing between components is generally 1.2 mm. Add the total area of PCB required for the optocoupler solution, and the designer must leave 134.5 mm2 space. Obviously, using the digital isolator solution, designers can already save about 28 mm2 of area.
After limiting the area of isolation devices, the designer should consider the supporting components required for the entire solution. Only two external bypass capacitors are required for digital isolators (such as ME1041). Assuming 0603 encapsulated capacitor is used, the occupied area is 2.5 mm2. For a typical optocoupler solution, the designer must add four resistors (5.1 mm2), four capacitors (5.1 mm2) and four front drive circuits (33 mm2), because most microcontrollers cannot handle the 10 mA power consumption requirements of their GPIO pins. So far, the designer can see that the digital isolator has obvious advantages when considering the area of PCB board.
Another design consideration related to PCB space is the drive of the high-voltage end of the isolation device. For BMS applications, it is necessary to balance the power consumption on the battery monitor to prevent the internal imbalance of the battery pack.
For the optocoupler solution, a separate DC-DC converter is required to provide the isolated working voltage to drive the high-voltage terminal interface, which will further increase the area requirement of the PCB board. In the digital isolation device, the designer can choose the digital isolator with integrated isolation power supply, which contains the SPI interface isolation channel, and also integrates the DC-DC converter function for driving the high-voltage terminal interface. Its packaging size is the same as that of ME1041 digital isolator, which will not increase the area requirement of PCB board.
Compared with the optocoupler solution, the digital isolator of GLM enables designers to create isolation circuits with lower cost, smaller size, higher performance, lower power consumption and more reliability. This isolation technology has a broad product portfolio, a proven record of industrial innovation and a firm commitment to excellent engineering design, and is ready to meet your isolation needs.