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HEF4051B multiplexer protection
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edba:
Hi

I am using the HEF4051B 8 channel analogue multiplexer as a switchable input to an ADC. The eight inputs goto a connector which then connects to the outside world. I was wondering about the protection you should provide for the HEF4051B? The HEF4051B does have internal protection circuit with clamping diodes. Is it ok to rely on this or should you provide additional protection?
aldi:
Protection against what? Surges? ESD? Faulty wiring by the user?

The internal clamping diodes are rated for +/-10mA if I read the datasheet correctly, so a current limiting resistor is a good start. If you want to clamp higher currents you can add external diodes, with a better forward voltage spec (=lower) than the internal diodes.
T3sl4co1l:
If the usual suspects (noise, ESD), a series resistor, filter cap, clamp diodes, and another series resistor is a good idea.

BAV99 is a good enough diode for clamping.  You probably don't want to use schottky (BAT54S being the other common choice) for analog signals due to leakage current.

Tim
edba:
Trying to protect mainly against ESD but these are user inputs so just wondering what other people do. I have initially designed in a series 100R resistor with 10nF cap to GND.

On analogue input expansion cards just wondering what sort of protection they put on the inputs.
edavid:
Depending on your budget, you could use a fault protected multiplexer like the ADG528.
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