introduction As the world energy crisis approaches, new energy-driven cars are about to face mass production and enter the market. For example, hybrid and electric vehicles (HEV / EV) introduce 400V and higher voltage designs into the automotive and transportation fields. To deal with such high voltages and large currents in a harsh automotive environment, a highly reliable and long-term stable working solution is needed to effectively isolate this high voltage from other electronic functional circuits. 1 Isolation requirements in traffic applications The hybrid and electric drive systems used in cars, trucks and motorcycles have created new and unknown challenges in the transportation industry. The original 12V voltage network now needs to be supplemented by 400V or higher battery and power supply systems, which puts forward a series of new requirements for automotive OEMs and system module suppliers. All functions in hybrid / electric vehicles such as high-voltage batteries, DC / DC converters, inverters for driving motors, and on-board charger modules connected to 230V / 380V grids have isolation requirements (Figure 1 ). Figure 1: Typical system architecture of an electric vehicle. Compared to industrial applications, automotive and transportation applications have different requirements for isolation. It is of course necessary to be solid and reliable, and it must also have strong resistance to magnetic "noise". The high power level in the car (such as a 100KW motor working at 400V, which means an operating current of 250A) will generate a strong magnetic field in the car that must be properly handled. The service life of the parts used must be long enough to meet the life expectancy requirements of the vehicle; for example, it must meet decades of use in large transportation applications. Products used in the automotive environment will drive the requirements for automotive application quality (Q1) and the operating temperature range of -40 to + 125 ° C. At the same time, cost pressures in these areas will drive higher system integration requirements. Therefore, single-chip products with isolation functions, such as CAN transceivers, ADCs, or gate drivers, have shown advantages. 2 Different digital isolation technologies In principle, there are four different digital isolation methods: optical, inductive, capacitive, and radio frequency. The first three methods are described below. Optical isolation technology uses a transparent insulating isolation layer for optical transmission to achieve optical isolation. By driving LEDs (Light Emitting Diodes), digital signals are converted from electricity to light. Then transmit this optical signal through the isolation layer, and then use optical detection components (photodiode, phototransistor) to convert the optical signal back to electrical signal. The main advantages of optical isolation are that light is immune to electric or magnetic fields and has the potential to deliver static signals. On the receiving side (flipside) of the isolation layer, the operating frequency (transmission speed) of the optical isolator is limited by the relatively slow characteristics of the LED. For hybrid / electric vehicle applications, the limited lifetime of optical isolation is a major disadvantage. With the passage of time, the efficiency of LEDs will decrease, so the signal drive current needs to be increased (usually starting from 10mA), so with the passage of time, this optical isolation will eventually fail to function. Inductive isolation uses changes in the magnetic field between the two coils to achieve communication across the isolation barrier (isolaTIon barrier). One advantage of the inductive isolation method is the difference between common mode and differential transmission, which means that it has good noise immunity. The disadvantage of this method is that it may come from the distortion of the magnetic field, which is very common in the motor control environment of hybrid / electric vehicle applications. Capacitive isolation uses changes in the electric field across the isolation barrier. The advantages of the capacitive isolation method are stronger immunity to magnetic fields and a longer system life. The transmission speed of capacitive isolation and inductive isolation is similar. However, the disadvantage of the capacitive isolation method is that there is no differential signal (that is, the signal and noise share the same channel). In addition, as with the inductive isolation method, they cannot directly transmit static signals (must be encoded with frequency signals first). 3 Isolation products An example of the capacitive isolation method is the Texas Instruments ISOxxxx series. Figure 2 is a simplified architecture diagram of the ISO72xx system. The ISOxxxx components are integrated in a single package, integrating two dies placed on separate lead frames, and transmitting and receiving chips. Only two bonding wires connect the two dies. The actual isolation function implemented on the receiver is based on silicon dioxide (SiO2, ie glass), with copper and doped silicon as the substrate electrode capacitors (Figure 3). The use of SiO2 can bring the advantages of high reliability and long life. Figure 2: TI's ISO 72xx series architecture diagram. Figure 3: TI's ISO72xx series of bare-die photos, with silicon dioxide isolation on the receiver chip on the right. Both channels allow DC and AC communication at the same time, in addition, it also has a fault prevention function. The basic AC channel uses an input signal and transmits it through a differential pair consisting of isolation capacitors after filtering. Then, the input end of the Schmitt trigger on the receiving chip detects it, and finally outputs the received signal through the output buffer. It can achieve very high-speed transmission, slight pulse width distortion and short transmission delay, but cannot send DC signals. SHENZHEN CHONDEKUAI TECHNOLOGY CO.LTD , https://www.szfourinone.com
