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Whats the output of non selected analog multiplexer pins?

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jcestela

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What is the output of a non selected pin of a analog multiplexer? lets say you have a 3 to 8 mux, which has pin 1 selected, so the voltage in the input will be present in pin 1. However the other pins (2 to 8 ) are in what state? are they grounded or are they at a very high impedance? I need for all the non selected pins to be grounded, however the pins are not behaving this way... but if I measure with a voltmeter they read 0 volts... thanks in advance!
 

betwixt

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Re: Whats the output of non selected analog multiplexer pins

Consider the multiplexer to be just like a bank of mechanical switches. The one you select is connected from input to output, the ones not selected are disconnected.
Apart from the tiny capacitive loading and possibly a tiny leakage current, the unused inputs are floating.

If you are not using some inputs, either ground them directly or through pull-down resistors to prevent static build up. This is good practice for any unused input on any IC.

Brian.
 

snafflekid

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Re: Whats the output of non selected analog multiplexer pins

If you want the unused pins grounded, you need to add your own pulldown resistors. They are kind of floating, but there are parasitic diodes on them that will pass leakage currents.
 

vistapoint

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Re: Whats the output of non selected analog multiplexer pins

It's 'high-impedance'.

In other word, theorectically it's 'anything' in term of voltage. If you use a pull-up it's high and if pull-down it's low.

In reality high impedance doesn't mean infinite impedance. And it's high impedance to somewhere with a fixed voltage level.


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