In high-voltage applications, it is critical to achieve effective electrical isolation to avoid unwanted leakage current flowing between two parts of the system with different ground potentials (GPD). As shown in Figure 1 (left), the DC return current from the input to the output can cause a potential difference between the two grounds, resulting in reduced signal integrity and poor quality. This is where isolators (i.e. isolated gate driver ICs or digital isolators) come in, as shown in Figure 1 (right). Isolators allow only communication signals and power to pass through the isolation barrier by blocking the flow of DC and uncontrolled AC current between two parts of the circuit. In addition, isolators provide the necessary protection for human interaction with high-voltage systems and provide level shifting functionality to enable interaction between systems of different voltage levels.
Figure 1: DC return currents between two parts of a system create unwanted ground loops (left), while galvanic isolation prevents unwanted ground loops by breaking the ground connection (right)
Generally speaking, isolators can be roughly divided into two categories: optical isolators and digital isolators.
An optoisolator, often referred to as an optocoupler, is an analog isolation product that uses light to transmit signals through an isolation barrier. Optical isolators have been widely used in the industry for decades because of their early emergence and competitive prices. However, the switching speed of LEDs limits the achievable data rate to a few megabits per second. In addition, optoisolators require additional circuit components to provide proper bias and drive the integrated LED. This takes up additional PCB area and increases the cost (BOM) of the application. Although current technology can integrate external bias and drive circuits in one package to minimize PCB size and achieve higher speeds, this will greatly increase the cost of the solution.
Figure 2: Cross-section of the coreless transformer used in Infineon’s ISOFACE™ digital isolators 2DIBx4xxF
Digital isolators, on the other hand, use capacitive or electromagnetic isolation techniques to transmit signals. These techniques drastically reduce the size of the isolation components while achieving a long lifetime. Digital isolators have recently become the first choice for many applications due to the following advantages over opto-isolators:
First, optimize system BOM material cost and reduce PCB area; Second, accurate timing characteristics, lower power consumption; Third, enhanced common-mode transient immunity (CMTI); Fourth, reliable insulation life , obtained the certification of the component level standard IEC 60747-17; Fifth, integrate more functions, such as: input filter, transceiver (eg: CAN, RS-485), output enable option.
Digital isolators have clear advantages in industrial applications, such as in isolated low-voltage DC-DC modules and isolated CAN and UART communications.
In low-voltage DC-DC power modules, digital isolators can ensure safe isolation and robust data transmission. Take Infineon's ISOFACE™ dual-channel digital isolator 2DIB0410F as an example. This product uses a patented coreless transformer (CT) technology to transmit signals through a coupling transformer. In addition, the product integrates functions such as jitter filter, communication modulation, watchdog and undervoltage lockout (UVLO) to ensure robust and safe data transmission even in severe high voltage and noisy industrial environments.
In isolated CAN and UART communications, the digital isolator's high common-mode transient immunity (CMTI) and extremely low pulse-width distortion (PWD) characteristics enable reliable communications. Taking Infineon's ISOFACE™ dual-channel digital isolator 2DIB1401F as an example, this product can provide high common-mode transient immunity (CMTI) and extremely low pulse-width distortion (PWD), which are all necessary for reliable communication. key features required. In addition, the default high output state of the isolator ensures that the communication line remains clear, preventing potential power loss on the input side.
To sum up, digital isolators are gradually replacing traditional optical isolators and becoming the mainstream choice in industrial applications due to their compact size, efficient functions, and excellent performance. With the continuous development of technology, we have reason to believe that digital isolators will play a more important role in future industrial applications.
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