Figure 8-6 shows the simple protection scheme implemented in the design to mitigate issues that arise from voltage and current transients on the bus. These transients have two main components: high-frequency and high-energy. These two components can be leveraged with a strategy of attenuation and diversion by the protection circuitry to deliver robust immunity.

Figure 8-6 Loop Input Protection

Attenuation uses passive components, primarily resistors and capacitors, to attenuate high-frequency transients and to limit series current. Use ferrite beads to maintain dc accuracy while still delivering the ability to limit current from high-frequency transients. This circuit uses a capacitor placed across the input terminals, as well as ferrite beads in series with the terminals.

Diversion capitalizes on the high-voltage properties of the transient signals by using a diode to clamp the transient within supply voltages, or to divert the energy away from the system. Transient voltage suppressor (TVS) diodes help protect against transients because TVS diodes break down very quickly and often feature high power ratings that are critical to survive multiple transient strikes.

A rectifier is also implemented for reverse polarity protection so that the design can be connected to the bus regardless of the pin orientation or polarity without damage to the design.