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TMUX4157N: NC at S2 makes 1V available at D output pin

Indira M
Prodigy 100 points
Part Number: TMUX4157N


Tool/software:

Hi Greetings!

We use TMUX4157N IC. 

At S1, GND(ground) is connected, for logic 0.

At S2, NC (no connection), for logic 1.

I expect, the output line be grounded for logic 0

and the output line be OPEN for logic 1, as S2 is NC.

But I observe 0v at the output when Logic is 0.

But 1.16V at the output, when Logic 1 is given, which is not expected. NC 

Why is it giving 1.16V?

Thanks in advance.

Thanks & Regards,

Indira

  • 0
    Guru 318050 points

    When the pin is not connected to anything, it is floating and does not have any specific voltage. If you do try to measure it, the result is an effect of the measurement method.

  • 0
    TI__Prodigy 360 points

    Hi Indira,

    As Clemens stated, if S2 is left floating, and the SEL logic is high (1), there should be no voltage reading at S2 or D because there is no source tied to it.

    Also, unused signal path inputs (Sx or D) should be connected to ground and should not be left floating. This is stated in the datasheet in section 8.4 on pg.16. 

    Regards,

    Justin

  • 0 in reply to Clemens Ladisch
    Prodigy 100 points

    Yes, thanks, agree with you. When I use manual jumpers, the voltage measurement gives few mV indicating it is not having any connection. But only when my spdt switch is used, I am getting 1.16V.

  • 0 in reply to Justin Lewis
    Prodigy 100 points

    Yes, right.

    And thanks for pointing out 8.4 which I have missed to see, which I should not have done. 

    This mux is SPDT switch. Instead I will try with SPST switch.

    In SPDT, for both control logic, internal switch is active and closed. In SPST, for one control logic, the internal switch would be open which might help me out, I think.

    The output of the switch should be left open as required by LD1255R SLD driver IC.

    Thanks for your support. Meanwhile further guidance relevant this above said requirement is also welcome.

    Thanks and Best Regards,

    Indira