How does magnetic coupling isolation of I/O modules prevent interference?

Magnetic coupling isolators, based on the transformer coupling principle, possess unique EMC immunity characteristics. Magnetic couplings typically exhibit high common-mode transient immunity, exceeding 100kV/μs, superior to most optocouplers, effectively resisting rapid common-mode voltage transients. Internally, they employ differential transmission, providing natural suppression of common-mode noise. Magnetic couplings do not suffer from the LED aging issues of optocouplers, resulting in a longer lifespan, but they may be sensitive to extremely low-frequency or DC magnetic field interference, despite internal shielding. When using magnetic couplings, to ensure optimal performance, high-quality decoupling capacitors, typically 0.1μF MLCCs, must be placed near the power supply pins.

During PCB layout, avoid placing high-current switching traces below or near the magnetic coupling to prevent magnetic field coupling interference. The input and output ground planes of the magnetic coupling should be completely separated by a gap below them. For high-frequency noise, a small resistor can be connected in series on the differential signal lines of the magnetic coupling, or a common-mode choke can be added. Compared to optocouplers, magnetic couplers typically consume less power and are faster, but optocouplers may still be chosen for applications requiring extremely high isolation voltages or where cost is extremely critical. The choice should be based on specific immunity test requirements.