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Original question:

CD74HC4067: What should be done with the unused input pins of the multiplexer IC ?

internal pull up or pull down resistors present

Varghese Thomas Thoppil
Prodigy 70 points
Part Number: CD74HC4067

Hi

I would like to know that if the mux CD74HC4067 has internal pull up or pull down available on the input pins ? 

  • 0
    Guru 283700 points

    Analog switches are designed to affect analog signals going through the switch as little as possible, so there are no pull-up/-down resistors.

    Why do you want resistors? If the pins are unused, you can connect them directly to VCC or GND.

  • 0 in reply to Clemens Ladisch
    Prodigy 70 points

    Hi Clemens 

    Thanks for the reply

    I am actually leaving the unused pins unconnected. Based on the answer I got from the forum, I understood that unused pins could be left floating.

    But I came to know from forum that in analog multiplexers cmos transistors are configured as transmission gates. So unused inputs doesnot require external pull up or pull down. But in the datasheet of CD74HC4067 block diagram, I am not sure if the inputs are connected to transmission gates. In the block diagram the inputs are shown to be connected to P N block. Regarding details on P N block is not given in the datasheet. So I am confused if the blocks are actually transmission gates or any other circuit with internal pull up or pull down ? 

    Also I would like to know based on your above reply that why you have recommended connecting unused pins directly to Vcc or GND. Is it safe doing so without pull up or pull down resistor ?

  • 0 in reply to Varghese Thomas Thoppil
    Guru 283700 points

    That block with the "P"/"N" labels is a transmission gate. (There isn't really a standard way to draw them, and this datasheet originated from Harris.)

    I assumed you wanted to use the pull-up/-down resistors for some digital application. But for unused channels, connection does not matter.