Why CMTI Matters: The Unsung Hero of Isolation Technology

By Aditya Ambardar, Business Unit Manager for Switching Power

In today’s electrified world, isolation products like digital isolators and isolated gate drivers are the backbone of safe, reliable power systems. Whether it’s electric vehicles (EVs), solar inverters, or data centers, these devices bridge high-voltage power domains and low-voltage control circuits, protecting both equipment and people. But as power electronics evolve, one specification is becoming increasingly critical: common-mode transient immunity (CMTI).

What is CMTI?

CMTI measures how well an isolation device can withstand rapid changes in voltage between its two sides—think of it as the device’s ability to ignore electrical “noise” that could otherwise cause errors. It’s typically specified in volts per nanosecond (V/ns) or kilovolts per microsecond (kV/µs). In environments with fast-switching transistors (like SiC or GaN), voltage can change at rates exceeding 100V/ns. If an isolator’s CMTI isn’t high enough, these transients can cause false logic transitions, communication errors, or even critical failures in gate drivers.

Why is CMTI Vital?

Imagine an inverter switching 800V in just 8ns—a whopping 100V/ns. If your isolator cannot handle that, you risk spurious resets, miscommunication, or shoot-through events in half-bridge circuits. As electrification pushes voltages and switching speeds higher, robust CMTI is no longer optional; it is essential.

Figure 1: Comparison of a device from Diodes Incorporated and two equivalent devices; good CMTI does not let spurious spikes pass through

How Diodes Incorporated Delivers High CMTI

The RobustISO™ technology from Diodes Incorporated (Diodes) is engineered for high CMTI. For example, the API772x family provides at least 150V/ns CMTI, meaning a 1500V spike in 10ns will not upset the signal. This is achieved through:

Thicker insulation barriers for higher breakdown voltages
Differential signal transmission to cancel out common-mode disturbances
CMOS input/output stages that are designed to prevent parasitic coupling
Integrated noise-filtering logic that ignores glitches unless they persist long enough to mimic a valid signal

These innovations ensure signal integrity even in the harshest environments, such as EV drivetrains, solar inverters, motor drives, and more.

What Should Engineers Look For?

When selecting isolation products, prioritize:
CMTI rating (higher is better, especially for SiC/GaN applications)
Isolation voltage (working and surge ratings)
Propagation delay and data rate (for timing-critical signals)
Package creepage and clearance (for safety compliance)
Certifications (UL, VDE, IEC, automotive grade)

The Future of Isolation

As systems move to even higher voltages and faster switching, isolation technology must keep pace. Diodes Incorporated is pushing boundaries with thicker insulation barriers, advanced packaging, and integrated diagnostics for functional safety.

CMTI is the difference between a robust, reliable system and one plagued by glitches and failures. With Diodes’ RobustISO™ isolators, you can design with confidence, even in the most demanding environments.

RobustISO™ is a trademark of Diodes Incorporated.

The Diodes logo is a registered trademark of Diodes Incorporated in the United States and other countries.

All trademarks are the property of their respective owners.

Posted in Technology, Tagged Analog Products, Isolation, RobustISO, Posted 25 days 以前 by , Aditya Ambardar | Business Unit Manager for Switching Power