Analysis of technical solutions for digital isolation and traditional isolation solutions

Inappropriate isolation circuit design causes equipment damage, and even cases of electric shock accidents are not uncommon. For this reason, many safety isolation design performance requirements and series mandatory certification standards have been proposed in the industry. Appropriate isolation measures must be adopted in the design. In addition to safety considerations, the use of isolation measures can also help reduce ground loop noise.

However, isolation measures inevitably introduce limitations in terms of latency, power consumption, cost, and size. Especially for many years, the only reasonable choice for achieving safe isolation is the optocoupler. With the increasing speed of data transmission in recent years, the increasing power consumption, cost, size, and increasingly demanding performance requirements, traditional optocouplers have also exposed many shortcomings - large circuit, integrated The degree is not high, and the optical coupling device itself has disadvantages such as loss of speed, slow speed (general data rate is less than 1 Mbps), and large power consumption. Especially in the process of temperature and aging changes, the performance is extremely unstable, which brings many limitations for its application. These problems are particularly prominent in applications where industrial and medical requirements are high.

The main structure of the isolator is roughly four: one is the traditional optocoupler; the other is the integrated transformer (magnetic coupling); the third is the integrated capacitive coupling; the fourth is the discrete transformer coupling. To overcome the many shortcomings of opto-isolation technology, many semiconductor companies have begun to develop non-opto-coupled isolator solutions. Analog Devices was the first company to introduce a new digital isolator solution, and in 2001 was the first to introduce a standard digital isolation product based on its patented iCouple magnetic coupling isolation technology.

Figure 1: iCoupler chip-scale transformer structure

The iCoupler technology is a chip-sized transformer, and each iCoupler channel consists of a CMOS interface circuit and a chip-scale transformer. The key to the iCoupler device is the planar transformer that can traverse the isolation insulator, transmitting and receiving signals. It provides isolation and eliminates the problem of excessive photoelectric conversion, large timing error, and low data rate in the optocoupler. The unique structure enables iCoupler digital isolators to achieve many of the performance advantages of leading optocoupler devices: static/dynamic current is smaller, power consumption is only 1/10 to 1/50 of optocoupler; thousands of volts (5000V) can be realized The isolation, the key to its high withstand voltage is between the top and bottom coils of the transmitting and receiving transformers, using a polyimide material with a thickness of 20μm as the isolation layer; the transmission speed is faster, much higher than the traditional optocoupler, up to 150Mbps Longer life, up to 50 years in the range of high voltage and breakdown resistance; can integrate other functions in the standard CMOS process; can achieve isolated power inside the chip, and has a smaller volume and thickness.

Figure 2: Performance comparison of optocoupler and iCoupler digital isolator

These products can be used in almost all applications, including medical equipment, instrumentation, network equipment, battery charging systems, industrial process control, new energy, lighting and building control, automotive systems, industrial fieldbus, and more. Currently, more than 850 million isolated channels worldwide use iCoupler technology. This article will share three typical application cases to see what different performance features iCoupler can bring in these system designs.

The unique environment for industrial applications has different requirements for isolation technology than other system designs, including wider ambient temperatures, higher reliability, and higher performance. In addition, the cost, integration, power consumption and other characteristics are also factors that must be considered in many designs.

Electromagnetic flowmeters are one of the typical industrial applications. Due to its no pressure loss, electromagnetic flowmeters are not affected by viscosity, fluid density, temperature, pressure or conductivity, and are welcomed by high-precision measurement applications such as pulp, mud and sewage. However, since system power, central logic, communication, and I/O require isolation from 1 kV to 2.5 kV, requiring the ability to connect to different fieldbuses, proper isolation must be performed.

In the past, electromagnetic flowmeters mostly used optocoupler devices to achieve electrical isolation requirements in the system. However, due to the limited space inside the electromagnetic flowmeter, the system density is high and thus sensitive to device size. For portable electromagnetic flowmeters, in addition to size sensitivity, device power consumption is also a critical consideration. In recent years, more and more electromagnetic flowmeter manufacturers have abandoned optocoupler devices in isolation circuits and switched to iCoupler isolation technology with more overall performance advantages. One of the leading domestic manufacturers of electromagnetic flowmeters, Chengbo, used optocoupler devices in its early product designs, based on a comprehensive trade-off in cost, performance, size and integration complexity. Four-channel iCoupler digital isolation technology is used to achieve isolation, effectively reducing PCB footprint by 60%, requiring only 90mm & TImes; 80mm PCB area. In addition, in the new design, only the isolated circuit portion achieves 90% power savings.

Figure 3: Comparison of package dimensions for a well-known four-channel optocoupler (left) and ADI four-channel iCoupler (right).

A wide range of products offers a more targeted choice for such applications. The ADI's electromagnetic flowmeter reference design, which has a large number of applications in the industry, uses the 1kV four-channel digital isolator ADuM7441 for basic electrical isolation. Unlike most four-channel isolators in a 16-lead SOIC wide package, the device is available in a small 16-pin QSOP package, which saves almost 70% of board space while still withstanding high isolation voltages. And meet the regulatory requirements of UL and CSA standards (in the process of application). In addition, the ADuM7441 consumes very low power and consumes only one-tenth to one-sixth the power of comparable isolators at data rates up to 25 Mbps. If the design requires 2.5kV isolation, you can also choose the dual-channel digital isolator ADuM320x or the four-channel digital isolator ADuM140x. These two series of digital isolators are also based on ADI's iCoupler technology, which also has excellent low-power characteristics. Ideal for battery powered electromagnetic flowmeter designs.

In power metering, iCoupler digital isolation technology also forms an alternative to traditional optocouplers. DC-compatible current transformers have been used to detect AC currents in smart meters, but they have some drawbacks and are expensive. For some applications, shunt resistors are a better choice for current sensors because of their low cost, high linearity, and resistance to magnetic field interference. However, the shunt resistor does not have the electrical isolation characteristics inherent in current transformers. In smart meters that require isolation, digital isolators with isolated power technology combined with shunt resistors provide a good solution. The iCoupler digital isolators are widely used by power metering companies due to their superior performance over traditional optocouplers and support for a variety of serial communications (SPI, I2C or UART). In 2012, ADI introduced a 3-channel, ramp, ADC-based metrology application that integrates Analog Devices' iCoupler and isoPower patented technologies for three-phase energy metering applications, with a 5kV isolation barrier. Isolation signal transmission and DC-DC power conversion enable shunt resistor sensing components instead of current transformers, which greatly reduces cost and is immune to magnetic field interference and tampering.

The series of standards such as IEC-60601-1, EN 6061-1-2 and UL 6061-1 are basic safety standards for medical electronic products. The requirements for protection against electric shock hazards are clearly defined. The application of isolation technology is to meet the requirements of these standards. The essential. To meet these standards, Lantronix, the world leader in secure communications solutions, uses iCoupler digital isolation technology for galvanic isolation on every port of its new EDS-MDn multiport medical device server. EDS-MD's galvanic isolation provides the highest level of security for such connected devices, helping to ensure that ground faults, functional faults, etc. are limited to a single port, without affecting the integrity or availability of the EDS-MD itself or other connected devices. .

With these isolators, Lantronix's design engineers were able to increase the total number of isolated channels, ultimately resulting in a four-fold increase in data rate and timing specifications over optocoupler-based designs. By abandoning larger optocouplers and other additional external components, Lantronix designers have reduced system size and system integration while reducing overall design complexity and cost. The reduction in the number of EDS-MD components reduces the total board space by 40% compared to competing products, which in turn helps the point of care save valuable bedside space. The iCoupler digital isolators consume up to 90% less power than optocouplers, giving Lantronix's EDS-MD design engineers greater design flexibility, making them easy to achieve power targets.

Figure 4: Lantronix's new EDS-MDn multiport medical device server.

There are many similar applications - Beijing Chaosi Electronics, one of China's largest medical device manufacturers, has also adopted the iCoupler digital isolation product in its full-featured patient monitor MMED6000DP series, which also abandoned the optocoupler devices that have been used. The combination of iCoupler and isoPower provides the best isolation platform for the MMED6000DP, enabling the monitor to fully surpass the optocoupler isolation scheme in terms of performance, integration, cost and size under the condition of 5kV isolation.

The satellite's power system is critical, and any failure can cause serious damage to the spacecraft, making it impossible to complete the mission. The Siemens Aerospace Business Group's PowerSCOE project is one in which each channel contains auxiliary analog inputs and digital and analog outputs, so the biggest challenge is to ensure that 100 channels are isolated from each other. With more than 100 analog and digital I/Os on the PCB, traditional optocouplers and DC/DC converter solutions can't do anything about such high PCB densities.

The system ultimately uses ADI's highly integrated iCoupler digital isolation technology. Digital isolators with integrated isoPower DC/DC converters based on iCoupler technology, isolator integrated DC/DC conversion at 5.0 V (5.0 V input supply) or 3.3 V (3.3 V or 5.0 V input supply) The device can provide an isolated regulated power supply of up to 500mW. iCoupler chip-scale transformer technology provides isolated power and isolating four-channel logic signals, eliminating the need for discrete isolated DC/DC converters in low-power isolation designs. As a result, this solution uses fewer, smaller, and more cost-effective solutions than optocouplers and discrete solutions.

Using highly integrated digital isolators, Siemens Aerospace's design engineers were able to increase the number of isolated data ports that a control module can accommodate without having to increase the module size, even if each port requires its own isolated power supply. The PowerSCOE protection board has 170 iCoupler devices. If other solutions, such as optocouplers and discrete isolated DC/DC converters, are used, the control module will be much larger than the current size of 380 mm x 470 mm.

With iCoupler digital isolators, design engineers can get rid of the cost, size, power, performance and reliability constraints of optocouplers in traditional designs, enabling excellent isolation performance in their designs. ADI offers a broad portfolio of iCoupler digital isolation products including: single-channel to 6-channel standard isolators; digital isolators with isolated power supplies - isoPower; USB isolators; isolated MOSFET drivers; Regulated power supply; I2C bus digital isolator; CAN bus isolated transceiver; RS485 isolated transceiver; RS232 isolated transceiver; Σ-Δ isolated modulator. These devices are fully versatile for a variety of system isolation needs.

Choosing the right isolation technology also needs to understand the isolation strength requirements in the application. The following problems need to be determined: the working voltage in the actual application; the grid condition of the equipment (220V civil grid/industrial power grid); the actual application environment (elevation) Height/humidity conditions/temperature conditions/contamination conditions); isolation protection level adopted in the application; type of protection object (functional isolation/basic safety isolation/enhanced safety isolation); which specific international safety specification the application should comply with; . In addition, you should also understand your requirements for isolator operating speed and interface: What is the highest rate in this application? How many channels do you need in a package? Timing requirements in this application (such as signal delay requirements), and whether additional functions (I2C/USB/RS-485/integrated isolated power) are required. Regardless of the needs, ADI's hundreds of digital isolators based on iCoupler technology are almost ready for the application.