By Christopher Nunes
What happens when your system needs to talk across noisy or high-voltage boundaries? Isolation steps in. In a previous blog post, we discussed the fundamentals of isolation and its importance in system design. Now, let’s explore how to isolate field-bus interfaces such as RS-485 or CAN. There are four primary approaches, each suited to different application needs. We'll begin with the most intuitive to visualize and progress toward the simplest to implement. Every isolated transceiver architecture presents its own trade-offs, so understanding these differences is key to selecting the right solution for your application.
Digital Isolator + Non-Isolated Transceiver
The first architecture we’ll explore is the most basic: a digital isolator paired with a non-isolated field-bus transceiver. In this setup, the digital isolator transfers signals across the isolation barrier, which are then fed into the transceiver to convert them into field-bus signaling.
Figure 1: A Digital Isolator and Non-Isolated Transceiver Architecture
Advantages:
- Simple and intuitive—it's easy to visualize how the signals flow.
- Flexible—if your application requires additional control signals, you can use multi-channel digital isolators like the 6-channel ADuM361.
Drawbacks:
- Requires more PCB space due to the use of two discrete components.
- Needs an external power supply for the transceiver side.
Because of these limitations, this architecture has largely fallen out of favor—especially now that integrated isolated transceivers offer more compact and efficient solutions.
Field-Bus Isolators
Next up is the isolated transceiver architecture, which integrates both the digital isolator and the non-isolated field-bus transceiver into a single package. This streamlined design simplifies implementation by reducing the component count to just one discrete part, saving valuable PCB space and easing layout complexity. When implementing this architecture, for RS-485, consider the ADM2495E or the MAX2202X family, while for CAN, the ADM305X family offers robust options.
Figure 2: A Field-Bus Isolator Architecture
Advantages:
- The integrated design simplifies implementation and saves valuable PCB space.
Drawback:
- Like the previous architecture, this setup still requires an external power supply to energize the isolated side of the device. If you're using a push-pull DC-to-DC transformer to provide isolated power, the next architecture we’ll cover might be an even better fit.
Integrated Transformer Driver + Field-Bus Isolator
A widely used method for powering the isolated side of a transceiver is through a DC-to-DC converter power supply structure. These isolated transceivers feature an integrated transformer driver on the logic side, which drives an external transformer to supply power across the isolation barrier. Structurally, it’s similar to the previous architecture—but with the added benefit of built-in transformer drive capability. For RS-485, check out the ADM2482E and MAX14859. For CAN, the MAX14882 is a solid choice.
Figure 3: A Field-Bus Isolator with Integrated Transformer Driver
Advantages:
- Combines two discrete functions into one compact package, saving valuable PCB space.
- Ideal for systems powered by higher-voltage batteries, offering excellent power efficiency—especially useful when designing your voltage domain structure (which we’ll dive into in the next blog post).
Drawback:
- Requires an external transformer to supply power across the isolation barrier.
But what if you’d rather avoid using an external transformer altogether? That’s where our next architecture comes in.
Integrated isoPower Transformer + Field-Bus Isolator
The final architecture is the most compact and integrated solution for isolated transceivers. It features a built-in DC-to-DC converter that powers the isolated side directly from the logic-side supply—typically 5 V or 3.3 V. Devices like the ADM2895E exemplify this design, offering a true single-package solution that minimizes PCB footprint and simplifies implementation.
Figure 4: A Field-Bus Isolator with Integrated isoPower Transformer
Advantages:
- Ultra-compact—ideal for space-constrained designs.
- Simplifies layout and reduces component count.
Drawback:
- The internal DC-to-DC converter is less efficient than external solutions. It’s designed solely to power the isolated side and cannot support additional external components.
Conclusion
Each isolated transceiver architecture has trade-offs and is best suited for specific application needs:
- Digital Isolator + Non-Isolated Transceiver: Ideal if you need to pair with a specific non-isolated field-bus transceiver.
- Field-Bus Isolator: A straightforward solution when an external power network is already available.
- Transformer Driver + Field-Bus Isolator: Perfect for designs with higher voltage supplies, offering maximum power efficiency.
- Integrated isoPower Transformer + Field-Bus Isolator: The go-to choice for ease of use and minimal PCB footprint.
Understanding these options helps you tailor your design for performance, space, and power needs. In our next blog post, we’ll explore isolated voltage domains—how they influence system architecture and how each transceiver architecture fits into each voltage domain structure.
See the blogs in the TranscendingConventionalFieldBus series.