any isolated RS-422 driver with no bit errors during EFT test?

Document created by analog-archivist Employee on Feb 23, 2016Last modified by analog-archivist Employee on Feb 23, 2016
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1.Do you have any RS-422 drivers and receivers capable of operating during the
IEC 61000-4-4 Electrical Fast Transient Burst Testing with no signal
degradation? If so, do you have any application notes and/ or evaluation boards?

2.We require protection against Surge, EFT and ESD. Isolation would be
EFT Burst Test is Level 4. In addition to protection, we need the equipment to
operate with normal performance during the test: specifically, with the RS422
signal held at logic 0 we don't want any logic '1' signal appearing at the
output of the receiver.

We cannot control where the customer will run the cable, so Surge will have to
be Level 4.

I have tried implementing Protection Circuit 2 of CN-0313, but using a DS8921M
receiver followed by an opto-coupler. The circuit survives the EFT Burst Test,
but the DS8921M output pulses to logic 1 during the test.

Did your lab tests find any  RS422 circuits which can operate with no bit
errors during the EFT Test?


1. We currently have a Certified EMC Compliant reference circuit CN-0313.
Please could you explain :
• Do you require protection against Surge (IEC 61000-4-5), EFT (IEC 61000-4-4),
and ESD (IEC 61000-4-2)?
• What level of Surge do you require protection against? Level 1, 2, or 4?
• Or are you only interested in protection against EFT?

The Circuit Note CN-0313 and Application Note AN-1161 discuss in detail some of
the considerations that were taken into account when designing this for the
ADM3485E. The ADM3485E is a half duplex TIA/EIA RS-485/RS-422 compliant part.
We have also lab tested the Full Duplex ADM3491E (this is a recent addition and
not detailed in AN-1161 or CN-0313).
Please see the attached ADM3491E protection circuit information. Protection
schemes 1, 2, and 3 offer the same level of EMC protection as those described
in AN-1161/CN-0313.

For other transceivers (ADM2587E, ADM2582E) the AN-1161 can be used as a
reference EMC protection solution. One important feature of these parts is the
integrated dc/dc converter which provides isolated power without using any
external component. However, solutions with the ADM2582E & ADM2587E would need
to be evaluated via labwork testing.

In our lab testing the ADM3485E and ADM3491E survived the EFT tests without
damage. However in some cases there were bit errors.
So the Circuit Note CN-0313 protection circuits will possibly have bit errors
during ESD, EFT, and Surge testing.

At the moment we don't have lab test results for our isolated transceivers.
This is something that will be worked on in the coming months.