Hi all! I'm designing a data acquisition system with a number of analog and digital I/Os. I'm wondering if it is wise (or even mandatory) to insert some kind of I/O protection. The system will work with low voltage signals (+-5V) with a bandwidth of 1MHz or less... Witch kind of protections are commonly used for this kind of sistems, and how are they implemented?
Thank you, Antonio
Just came across this 10 mins ago
(good bedtime reading for insomniacs) but may have some pointers for you
martin
A series resistor and clamping diodes to Vcc and Gnd will normally do. Gotchas include diode leakage fouling high Z input sources, and rise time slow down.
This depends very much on the application, the physical construction, country you want to sell it in,....
But if these I/O pins are touchable from (or at least close to) the outside and you want to pass the CE EMC testing, you will have to ask yourself (among other things) how these I/O pins will handle an 8kV (contacting) or 12kV (air) discharge from an ESD zapper.
But there are many other aspects to consider.
How to protect inputs again depends on a lot of factors. Usually a series resistor, a capacitor and a diode clamp (which may already be inside the chip you are connecting to) will work nicely. But an arrangement like that may mess up your IO specifications. There are also special components for protection like chokes and transzorbs.
I don't know about commonly, but this is what I'm doing in my current project
Panasonic EXC-CET222U EMI filter (L-C-L module, SMT)
Followed by a Littelfuse SP724AHTP clamping chip.
Then the signal goes into an 0603 star configuration which I can populate with a variety of other signal-specific discretes (like 1wire pullups). It's similar to this old schematic, which uses diodes instead of the clamp chip:
If you had done some searching you might have found my article series (starting at the link below) useful.
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