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What is the effect on ADG508A about a floating input?

Hi,

I'm working with two ADG508AKR connected to an ADC (AD7880CR) through an OP297GS.

On one of the multiplexer, I have an input which is an option to my design. When this option is not installed, the input is floating.

We are reading each channels (except the floating one) in a loop. In this loop, we are selecting the channel, then proceeding to the ADC conversion, then reading the ADC Data.

We observed some glitch when reading the ADC data around the floating input.

Is a floating input can cause an issue on the MUX selection?

Is there any recommendation about unused input? 

Thanks,

Sabine G.

  • Hi Sabine,

    Sorry for the late reply.  In general you should avoid floating an input to an unknown potenital.  It can cause issues with charge/voltage building up and then being discharged when the switch is closed.  There are several approaches but typically unused pins are grounded. 

    Regards,

    Eric.