How to select TVS and pressure-sensitive I/O modules?

When selecting TVS diodes and varistors for I/O modules, it's crucial to understand their protection objectives and characteristic differences. TVS diodes offer extremely fast response and precise clamping voltage, making them suitable for protecting voltage-sensitive semiconductor devices, such as chip pins. When selecting a TVS diode, the reverse operating voltage (VRWM) should be slightly higher than the maximum normal operating voltage of the protected circuit. The peak pulse current (IPP) needs to be estimated based on the potential transient energy. The clamping voltage (VC) should be lower than the maximum withstand voltage of the protected device. For data lines, low-capacitance models such as the ESDLC series should be chosen.

Varistors offer high current carrying capacity and low cost, but their response is slightly slower, the clamping voltage is less precise, and they are prone to aging. They are suitable for primary protection of power ports or applications where high precision is not required. When selecting a varistor, the varistor voltage (V1mA) should be approximately 1.2-1.5 times the peak operating voltage of the circuit. The maximum current carrying capacity needs to be selected based on the surge rating. Typically, both are used in combination: the varistor acts as a pre-amplifier to absorb large energy, while the TVS diode provides precise clamping. After selection, actual tests need to be conducted in the circuit to verify its actual clamping effect and reliability under transient events.