How to suppress I/O module DI interference?

To suppress interference in the digital input channels of I/O modules, a comprehensive approach is needed, addressing both common-mode and differential-mode interference. Connecting transient suppression devices in parallel at the signal input is the primary measure. For example, using a low-capacitance TVS diode like the ESDLC5V0D3B can effectively clamp high-voltage spikes caused by electrostatic discharge or fast transient pulses, while maintaining the integrity of high-speed signals. Simultaneously, to filter high-frequency noise on the lines, a safety Y capacitor should be added between the signal line and ground, used in conjunction with a common-mode inductor.

The CML3225A-510T series common-mode choke is recommended; it effectively suppresses common-mode interference introduced by long cables while having minimal impact on differential-mode signals. In PCB layout, filtering components in the DI circuit should be placed as close to the connector as possible. Signal ground and power ground should be connected at a single point via a ferrite bead to block crosstalk from ground noise. For dry contact inputs, a small resistor can be connected in series at the input, along with a capacitor to ground, to form an RC low-pass filter. The time constant needs to be set appropriately according to the signal frequency to avoid false triggering.