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Current consumption when the mux is enabled and disabled

Varghese Thomas Thoppil
Prodigy 70 points
Part Number: CD74HC4067

Hi

I am working on a project where 10 inputs of the CD74HC4067 mux are used to collect data. While the remaining inputs are left unconnected or floating. Mux is given a Vcc of 3.3V. I would like to know how to calculate current consumption when the Mux is enabled and Mux is disabled ? I have seen three current parameters given in the datasheet electrical specifications table : Quiescent current, logic input leakage current and switch off leakage current. I would like to know which of these parameters need to be considered when calculating the current during enable state and disable state. Also apart from these parameters any other current parameters will come into play or need to be considered ? It would be very helpful if someone could help me in calculating the current consumption in both enabled and disabled case.

  • 0
    Guru 285390 points

    CMOS devices do not need any current as long as they are not switching; the current consumption is entirely due to leakage currents.

    You have to add the quiescent current, the input leakage currents for all inputs pins, and the switch-off leakage current for any inactive I/O channel pins that are connected to an external voltage.

    Mux enabled or disabled does not make any difference (except in the disabled state, there is one more channel in the off state).

  • 0 in reply to Clemens Ladisch
    Prodigy 70 points

    Hi Clemens

    Thanks for the reply but I have some doubts based on the above reply. Sir, I would like to request you to please answer my doubts given below

    I agree with the statement "CMOS devices do not need any current as long as they are not switching and in this case the current consumption is only due to leakage currents" but I would like to know when we are selecting different input channels of the mux, in that case there is switching happening. So in that cases how will I estimate that current values

    I would like to know what did you mean by the input leakage currents for all input pins ? Is it the same as Logic input leakage current given in the datasheet. If Yes, then how we could calculate that value of all channels. I was asking just because in the datasheet it is given that Logic input leakage current has a maximum value as high as +/- 1uA. But they are not mentioned that it is for single channel or for entire 16 channels.

    Also I didnot understand the statement "Mux enabled or disabled does not make any difference (except in the disabled state, there is one more channel in the off state)." When mux is disabled all the channels are off right ?

  • 0 in reply to Varghese Thomas Thoppil
    Guru 285390 points

    To estimate the dynamic power consumption, see the CPD specification, and SCAA035. But at what frequency are you selecting different channels? If it isn't some MHz, the power consumption rounds to zero.

    The logic input leakage current is given per logic input pin. But only Sx and E are logic inputs; the others are analog I/Os. (And the maximum values given are for the worst case, i.e., highest temperature and age; typical values are orders of magnitude smaller.)

    When a channel is on, current flows through the channel and does not leak elsewhere. So the difference between E = 0 and E = 1 is that fifteen or sixteen channels are in the off state.