Enhanced Product ADM2795E-EP
Rev. 0 | Page 15 of 17
THEORY OF OPERATION
RS-485 WITH ADDED DO-160G EMC ROBUSTNESS
The ADM2795E-EP is a 3 V to 5.5 V RS-485 transceiver with
added robustness that reduces system failures when operating
in harsh application environments such as military and aerospace
(MILA) avionics for sensors, actuators, and engine control.
Lightning strikes to jet airliners are common, about once every
1000 flight hours. The DO-160G standard, Environmental
Conditions and Test Procedures for Airborne Equipment, is a
standard for the environmental testing of avionics hardware.
Many airplane manufacturers specify DO-160G Section 22,
lightning induced transient susceptibility, as a requirement for
critical systems, like guidance, radars, communications, engine
control, and heat and air controls. Aircraft radome, wing tips,
fin tips, nacelles, and landing gear are areas most likely to be hit
by lightning strikes.
The ADM2795E-EP integrates fully certified DO-160G EMC
protection on the RS-485 bus pins, with Section 22 lightning
protection. The ADM2795E-EP also provides Section 25 ±15 kV
ESD air discharge protection. For Section 22 lightning, the
ADM2795E-EP provides protection against Waveform 3,
Wav eform 4/Wavefor m 1, and Wave for m 5A to Level 4 using
33 Ω or 47 Ω current limiting resistors to GND
2
, or to Level 4
across the isolation barrier to GND
1
.
CERTIFIED DO-160G EMC PROTECTION
Table 11 details the open circuit voltage (V
OC
) and short-circuit
current (I
SC
) as specified in the DO-160G Section 22 lightning
induced transient susceptibility standard for Waveform 3,
Wave form 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 37. Due to
the high amounts of energy associated with the DO-160G
Section 22 lightning standard, the ADM2795E-EP was tested
using external 33 Ω or 47 Ω A pin and B pin bus current
limiting resistors for testing to GND
2
. These resisters were
required in addition to the ADM2795E-EP integrated EMC
protection circuitry. However, when testing to GND
1
, no
current limiting resistors are required. The ADM2795E-EP
iCoupler isolation technology protects the device in the
presence of these extreme transients.
Figure 37. DO-160G Section 22 Waveform 1 and Waveform 5A, and IEC61000-4-5
Surge Waveform
DO-160G ADM2795E-EP TEST DETAILS
Figure 38 and Figure 39 show the Waveform 3 test setup
coupling/decoupling network (CDN) and the Waveform 5A,
Wave form 4/Waveform 1 CDN, respectively. For testing to
RS-485 bus side, GND
2
, an additional 33 Ω or 47 Ω current
limiting resistance is added on both A and B bus pins. DO-160G
Section 22 testing is performed on one pin at a time. The test is
not performed in common mode. Table 12 and Table 13 show a
summary of the ADM2795E-EP certified test results.
Table 11. DO-160G Section 22 Pin Injection Level 4 and Level 3 Compared to IEC 61000-4-5 Lightning Level 4 and Level 3
DO-160G Waveform 4/Waveform 1
4 1500 V, 60 A 750 V, 150 A 750 V, 750 A 4000 V, 49 A
Table 12. DO-160G Section 22 Pin Injection Level 4 Certified Test Results
Testing to
GND
x
Current Limiting
Resistor
DO-160 Waveform 3;
1500 V, 60 A
DO-160 Waveform 4/ Waveform 1;
750 V, 150 A
DO-160 Waveform 5A;
750 V ,750 A
GND
1
None Pass Pass Pass
GND
2
47 Ω or 33 Ω Pass with 47 Ω Pass with 33 Ω Pass with 33 Ω
Table 13. DO-160G Section 22 Pin Injection Level 3 Certified Test Results
Testing to
GND
x
Current Limiting
Resistor
DO-160 Waveform 3;
600 V, 24 A
DO-160 Waveform 4/ Waveform 1;
300 V, 60 A
DO-160 Waveform 5A;
300 V ,300 A
GND
1
None Pass Pass Pass
GND
2
33 Ω Pass Pass Pass
0
100
200
300
400
500
600
700
800
0 20 40 60 80 100 120
CURRENT (A)
TIME (µs)
IEC 61000-4-5 SURGE
DO-160G SECTION 22
WAVEFORM 1
DO-160G SECTION 22
WAVEFORM 5A
15664-137
