Digital Isolators: What You Need to Know

Digital Isolators: What You Need to Know

Author: Emmanuel Onyema

When circuits communicate with one another, there is a chance that they may negatively impact each other. Signals originating from one circuit could damage the destination circuit or cause it to malfunction.

Over the years, there have been a few solutions to this problem. Historically, optocouplers — devices that isolate circuits  by physically separating high-voltage circuit systems from nearby low-voltage systems — were the main way to keep unwanted signals at bay. But technology has evolved, and digital isolators have become the industry standard today.

We’ll discuss the difference between digital and manual isolation, the benefits of digital isolation, and advice on how to switch from optocouplers.

Old School vs. New School Isolation

While optocouplers are still more prevalent, there are certainly benefits to digital isolation that can warrant the time and cost it takes to upgrade to digital isolators. Let’s take a deeper look at each option and assess the differences between them.

An optocoupler is a hybrid device that uses LED light to transmit data across an isolation barrier to a light detector. The LED turns on for logic High and off for logic Low.

Although incorporated in many designs, optocouplers are based on outdated technology that provides significant output variation over input current, temperature, and age. This means that optocouplers generally consume high levels of power, are prone to aging and temperature effects, provide limited data rates, often below 1 Mbps, and can produce noisy output signals.

On the other hand, digital isolation devices were created to meet safety regulations while maximizing the benefits of modern complementary metal oxide semiconductor (CMOS) technology. To do this, digital isolation devices use semiconductor process technology to create either transformers or capacitors to transfer data instead of light. With this technology, performance and feature integration are both improved.

The Advantages of Digital Isolation

Digital isolation offers several benefits compared to its manual counterparts like optocouplers. There are many drivers for digital adoption — system requirements, user safety, and adherence to safety guidelines, to name a few — but the biggest benefits are the simplest ones. Isolation components add value by enabling more functionality and higher efficacy when it comes to safety. Between performance and safety, it’s hard to argue digital isolation is superior to its predecessors.

Si86Sx Digital Isolators Block Diagram

Digital isolation components provide multichannel isolation solutions with a much smaller footprint, increase system reliability due to a lower failure rate, offer twice the electrical noise immunity, operate over a wider temperature range (-40°C to 125°C), and do not age or degrade over time. 

Additionally, isolation devices allow for multiple power domains to coexist and communicate, meaning sensitive circuits are protected from switching circuits. Modern digital isolation also allows for massive integration, meaning circuit component count can decrease.

In short, digital isolators operate more efficiently and thus perform better.

How to Make the Switch to Digital Isolators

If you think you’re ready to join the future and make the switch from optocouplers to digital isolators, what’s next?

When you’re looking at digital isolator options, feature set and isolation performance are the two main factors to consider. On the feature set side, consider the number of isolation channels and the channel configurations. Timing specifications, such as propagation delay, should also be appropriate for your system. On the isolation performance side, it is important to gain an understanding of the isolation rating your system needs. Factors such as transient noise immunity and electromagnetic emission profile are other considerations related to the isolation structure to think through.

Once you’ve nailed down your application’s needs, you’ll want to be sure that the devices meet appropriate safety standards required by end safety agencies such as VDE, UL, CSA, VDE, and CQC. These safety agencies use their component safety standards to qualify and specify either a safety component’s one-minute voltage withstand rating, which is typically 2.5 kVrms, 3.75 kVrms,  5 kVrms, or 6 KVrms or its lifetime working voltage, which is typically between 125 Vrms to 1500 Vrms.

Digital isolators provide an ideal upgrade solution to replace outdated optocouplers. Advanced optocoupler replacements are now available to replace 6- and 8-pin optocouplers, connecting directly to existing external optocoupler input circuits. These optocoupler replacements are useful in both new and retrofit applications, offer more than 10x higher reliability than optocouplers, use less power, and provide faster and more uniform timing performance. Put simply, modern optocouplers cannot match the performance and reliability of the latest generation of CMOS isolators.

To learn more about how to transition to digital isolators and Skyworks’ broad product portfolio of CMOS digital isolators, visit https://www.skyworksinc.com/Products/Isolation-Digital-Isolators.

Isolation

By Emmanuel Onyema Power Product Line Manager