How to Design with Capacitive Digital Isolators 1

Currently, safety regulations regarding the use and design of electronic devices are continuously emerging, making current isolators almost indispensable in all data acquisition and transmission systems. One method to prevent low-voltage circuits in control systems from suffering potential high-voltage damage to sensor and actuator components in an electric field is to use digital isolators. diode

The purpose of this article is to demonstrate how to simplify isolation system design. In addition to describing the basic functions of capacitive digital isolators and detailing the installation of isolators in signal paths, it also provides valuable reference insights on successfully designing circuit boards.  diode

The basic functions of capacitive digital isolators

Figure 1 shows a simplified structural diagram of a capacitive digital isolator, which consists of a high-speed signal path and a low-speed signal path. The high-speed path (blue section) transmits signals ranging from 100 kbps to 150 Mbps, while the low-speed path (orange section) transmits signals below 100 kbps down to DC.

Figure 1 Simplified Structure Diagram of Capacitive Digital Isolator

The high-speed signal processed in the path indicated by the blue section is divided into multiple fast transient pulse groups by capacitive isolation barriers. Subsequent flip-flops (FF) convert these transient pulse groups into pulses with waveforms and phases consistent with the input signal. The internal watchdog (WD) monitors the periodicity of the high-speed signal edges. Under low-frequency input signal conditions, the duration between consecutive signal edges exceeds the watchdog window, forcing the watchdog to switch the output switch position from the high-speed path (position 1) to the low-speed path  diode