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I'm using an TS12A4514 CMOS switch in order to isolate some digital lines from one device to another. Power rails are 5V & 0V (GND).

While the switch is enabled (enable input is 5V), input voltages both high and low register almost exactly the same on the output.

When the enable output is low (0V) the input is disconnected but I can see anywhere between 200mV to 600mV on the 'NO' terminal, regardless to what is connected to the 'COM' terminal. I have tried driving the enable pins with a low voltage and with an actual short to GND with a wire, saw no difference.

Currently there is nothing connected to the 'NO' terminals so they are floating in the air. The power supply comes from an NIDAQ device and so are the enable control and digital input signals.

Is there something fundamentally wrong with the circuit? Shown here below: The ICs are all decoupled with 100nF caps near them, not shown in the schematic. enter image description here

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    \$\begingroup\$ What is connected to the NO outputs of the switches when you are measuring the low levels? \$\endgroup\$
    – Elliot Alderson
    Commented Dec 8, 2021 at 15:43
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    \$\begingroup\$ The 5V supply is maintained? The 0.6V (assuming a 5V supply) implies a lot of current flowing, such as two outputs fighting. \$\endgroup\$
    – Spehro 'speff' Pefhany
    Commented Dec 8, 2021 at 15:47
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    \$\begingroup\$ @user733606 No, not the COM input...what is connected to the NO output pin of each switch. \$\endgroup\$
    – Elliot Alderson
    Commented Dec 8, 2021 at 15:55
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    \$\begingroup\$ It's impossible to answer unless you actually edit your question and show/detail what's connected to those pins, as people have asked. (Please don't dump a few words at the end with an 'Edit' banner, put the information into the actual question.) Don't run a bit-at-a-time Comment chat, it's not a discussion forum. Thanks. \$\endgroup\$
    – TonyM
    Commented Dec 8, 2021 at 16:28
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    \$\begingroup\$ @user733606, sounds like you have configured your MCU wrong then. What is the voltage on the MCU pins, when it is disconnected from the NO output pin? \$\endgroup\$
    – Linkyyy
    Commented Dec 8, 2021 at 22:06

1 Answer 1

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There is nothing wrong with the diagram provided. With a -94db OFF isolation, and Vin=0.3V, then Vout should be just under 6uV.

Either you are testing with a defective part, or the diagram is not telling us the whole story. Suggest you prototype one known-good part and re-test your theory, then start reviewing your board to find out what is different. Possibly using wrong pins on package (none were in the diagram for us to check), or the output is connected to another output trying to drive high.

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  • \$\begingroup\$ Pinout of the devices was checked and now I am trying to run with nothing connected to the 'NO' terminals. \$\endgroup\$
    – user733606
    Commented Dec 14, 2021 at 21:22

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