Reinforced Digital Isolator Ensures Safety in Industrial Environments

September 20, 2018

Christine Young By: Christine Young
Blogger, Maxim Integrated 

In industrial environments such as automated factories, high voltages are part of the landscape. Programmable logic controllers (PLCs), motor drives, certain power supplies, and even medical equipment and electric vehicles (EVs) all have circuits that must be protected from these voltages. Even more critically, people working in these environments must be guarded from electric shock. Digital isolation provides the means to do both, providing signal isolation and level-shifting to help ensure correct circuit operation and insulate users from electric shock.

Based on industry safety standards, industrial equipment needs to provide two levels of isolation or reinforced isolation between dangerously high voltages and human operators. At the same time, factory equipment needs to function for long periods of time without maintenance. Choosing the right digital isolation technology is key to addressing these challenges.

Isolation ICs provide complete galvanic isolation between two power domains, protecting circuits from high common-mode transients and faults and eliminating ground loops. In many applications, digital isolators are replacing optocouplers because they can reduce the power requirements and take up less board space while offering the same isolation capability.

Some digital isolators on the market do have drawbacks to avoid: high power consumption, significant heat generation, and the introduction of large propagation delays (which limit system reliability and throughput) are among the red flags. Maxim recently introduced a new 5kVRMS reinforced digital isolator that avoids these drawbacks, providing dual insulation barrier isolation for fast digital signals. The MAX22445 four-channel isolator is ideal for safe, high-throughput, compact industrial automation systems. Its 0.41mA per channel current consumption and 0.74mW power consumption at 1Mbps with VDD at 1.8V presents a 4x lower power consumption level that competing solutions. Its throughput is 2x greater than other isolators on the market. With a maximum propagation delay of 10.5ns and a maximum data rate of 200Mbps, you can achieve fast and accurate data acquisition and enable high-speed interfaces with wide timing margins.

Figure 1: Human operators along with the circuitry inside automated factory equipment need to be insulated against the dangers of high voltages.

Protecting Against High Voltages

Let's take a closer look at how the MAX22445 mitigates the challenges of designing high-voltage industrial equipment:

  • Redundancy for increased safety: The IC has two isolation barriers in series, and a two-die design with separate isolation barriers on each die. Should something happen to one of the die within the package, the other die still protects the user and maintains the isolation barrier. This configuration meets VDE and UL reinforced standards.
  • Long-term reliability: Low heat generation and low electron migration in silicon allows for stable performance in harsh, hot operating environments
  • Link robustness: The device's 200Mbps maximum data rate provides the fast dynamic performance that increases timing budgets and link robustness
  • Flexibility: For designers moving toward more universal industrial equipment designs, which may be used in safety-critical and non-safety-critical applications, the MAX22445 offers the flexibility for a wide range of applications and provides a wide supply voltage range

As an example application, consider how the MAX22445 can support a smart meter application, as shown in the block diagram in Figure 2. Here are the criteria that are important for smart meters and the specs provided by the MAX22445 to support these criteria:

  • Reinforced isolation for robust operation
    • Max VIOWM = 1500VRMS
    • Max VIOSM = 10kVRMS
    • 5kV of isolation
    • Low power
  • Low current (0.8mA/channel at 3.3V)
    • Low voltage (1.7-5.5V)
    • Low heat generation
    • High reliability
  • High dynamic performance
    • Low propagation delay (10ns max) for wide timing margins for SPI
    • Max data rate = 200Mbps

Figure 2: Smart meter application featuring MAX22445

So, if you're designing high-voltage industrial equipment, the MAX22445 provides an option for mitigating the associated dangers to users as well as the circuits inside the equipment.