How to Design with Capacitive Digital Isolators 2

Low speed paths have several more functional components than high-speed paths. Because low-frequency input signals require isolation barriers and prohibit the use of large capacitors, the input signal is used for pulse width modulation (PWM) of the carrier frequency of the internal oscillator (OSC). This constitutes a very high frequency that can pass through the capacitor barrier. Due to the modulation of the input, a low-pass filter (LPF) must be used to remove high-frequency carriers before the actual data is transmitted to the output.  diode

Installation position in the signal chain

Digital isolators are divided into single channel, dual channel, three channel, and four channel devices, which can achieve unidirectional and bidirectional operation. Their common characteristics are as follows:

-Does not comply with any specific interface standards;

-Using 3V/5V logic switch technology

-Specially designed for electrically isolated digital, single ended (SE) data lines

Although the last point seems to be a design limitation, Figure 2 shows how to isolate multiple interfaces, including low-voltage SPI, high-voltage RS232, differential USB, and differential CAN/RS485.  diode