Providing Certified Protection in a Small PCB Area

Table 2. DO-160G Section 22 Pin Injection Level 4 and Level 3 Compared to IEC 61000-4-5 Lightning Level 4 and Level 3.
Figure 3. DO-160G Section 22 Waveform 1 and Waveform 5A, and IEC61000-4-5 Surge Waveform.

Table 2 details the open-circuit voltage (VOC) and short-circuit current (ISC) as specified in the DO-160G Section 22 lightning induced transient susceptibility standard for Waveform 3, Waveform 4/Waveform 1, and Waveform 5A for pin injection testing. The peak currents for the DO-160G Level 4 tests are much greater than standard industrial surge IEC 61000-4-5 peak currents. The waveform shape and rise/decay times for the DO-160G standard are significantly longer than those specified by the IEC 61000-4-5 standard, as shown in Figure 3.

Figure 4. The ADM2795E-EP certified DO-160G lightning protection solution, which saves the designer significant PCB area.

Analog Devices’ EMC protected RS-485 transceivers provide certified DO-160G EMC protection on the RS-485 bus pins with Section 22 lightning protection. They also provide Section 25 ±15 kV electrostatic discharge (ESD) air discharge protection. For Section 22 lightning, the devices provide protection against Waveform 3, Waveform 4/Wave-form 1, and Waveform 5A to Level 4. Due to the high amounts of energy associated with the DO-160G Section 22 lightning standard, the transceivers were tested using external 33 | or 47 | A pin and B pin bus current limiting resistors for testing to GND2. These resisters were required in addition to the integrated EMC protection circuitry. However, when testing to GND1, no current limiting resistors are required. Figure 4 shows the total PCB area occupied by the ADM2795E-EP EMC protection solution. When compared to discrete solutions, the device saves the avionics designer up to 70% in valuable PCB area, as well as associated cost and weight savings.

This article was written by Richard Anslow, Product Applications Engineer, Analog Devices (Norwood, MA). For more information, visit here .