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SN74AUC2G53: floating supplies (GND as VCC and neg1.25V as Vee) to allow switching of negative DC voltage?

pinhas rosenfelder
Prodigy 40 points
Part Number: SN74AUC2G53
Other Parts Discussed in Thread: TMUX1133, CD74HC4053,

Tool/software:

I need to switch between 2 different negative voltages to the common output.

The negative voltages range between 0V and -1V

1) Can I connect the Vcc to GND, and the Vee to -1.25V (for example) - and then switch between the two voltages?

2) Regarding the select (A) voltage, if it is a square wave driving it (positive polarity source)  - can I AC couple it to the A pin?

and I assume I need to give it a DC voltage reference to the middle point desired.  would a voltage divider of 1K and 1K from Vee to GND work?  and do I need an AC coupled 50 ohm for a fast square wave?

  • 0
    Guru 318490 points

    AC coupling is possible as long as you ensure that the resulting signal is always inside the allowed voltage range.

    Do you really need to use this particular switch? There are switches with split supplies like the CD74HC4053 or TMUX1133.

  • 0 in reply to Clemens Ladisch
    Prodigy 40 points

    I need a switch that can switch at ~1ns switching speed.  I believe the others do not?

    And just to be sure I have this clear - in terms of the negative going supply and negative voltage through the switch (between VCC and VEE inclusive) - no problems are foreseen correct?

  • +1 in reply to pinhas rosenfelder
    Guru 318490 points

    Yes, my suggested devices are slower.

    All voltages at the SN74AUC2G53's pins are measured relative to the GND pin. Staying between GND and VCC guarantees that it will work.

  • 0 in reply to Clemens Ladisch
    Prodigy 40 points

    Thank you for the prompt reply.

    I realised I have more questions:

    1 - I am now unsure I have 100% understanding of the timing.

     
    A - The delay from INH input time switching to the switch COMMON physically switching from input Y1 to Y2 (or vice versa) I assume might vary part-to-part but can be calibrated out by a timing a shift in my system - correct?  and which of the switching times in the chart is this?

    B- which time in the spec specifies the "rise" or "fall" time of the actual "COMMON" signal between states when switching?  and how dependent is it on resistive and capacitive load?  (As that needs to fall inside the needed length of time window)

    C- is this rise and fall time dependent on the voltage difference between Y1 AND Y2?

    thanks

  • 0 in reply to pinhas rosenfelder
    TI__Mastermind 20645 points

    Hello Pinhas,

    A. Values might vary, please see table below.

    B. This sounds like the break-before-make timing spec, which this device doesn't have. All timing specs are dependent on resistive and capacitive loads.

     

    C. I wouldn't say dependent, but there will be a slight difference in rise/fall time between the two pins, since the voltage level the signals will be rising to is different. 

    Thanks,

    Nir 

  • 0 in reply to Nir Gilgur
    Prodigy 40 points

    sorry - I meant to write the A channel switching (that is what would trigger the switch better Y1 and Y2 inouts, correct)
    trying to get a handle on 
    1 - how long it takes from the "break" until the "make" plus the voltage shift that presumably happens (BTW what happens to the voltage in the interim after break?)

    2- how long delay from A input to Y1 break (which is basically propogation delay I guess - is that inlcuded in the Ten and Tdis times along with the voltage shift to the new level?)

    If the delay from A to break is stable I can calibrate it out witht he appropraite shift int he control signal to A - whcih would need to be placed in the right time window anyway.

    But I need Y1 to shift to Y2 (or vice versa) preferable over the span of <1.5ns, but I can probably handle 3ns for the first phase design

    thanks

  • 0 in reply to pinhas rosenfelder
    TI__Mastermind 20645 points

    Hello Pinhas,

    Yes, the logic pin A controls the switching between Y1 and Y2. 

    1. Unfortunately, we don't have break-before make data for this device.

    When a breaking occurs, the voltage might slightly dip because of leakage, but it will mostly stay in a floating state, since the switch is in high impedance mode. 

    2. Propagation delay is basically how long it takes a signal input to pass through the mux from source to drain. In the datasheet we show the delay between sending a signal to the logic pin A to toggle the switch and the output signal coming from the drain side. 

    As I mentioned earlier we don't have break-before-make information and due to the age of this device we don't really have data in our internal tools. What is in the datasheet is what we have. 

    Thanks,

    Nir 

  • 0 in reply to Nir Gilgur
    Prodigy 40 points

    thanks.
    ANy idea if there is any sort of evaluation board or generic evaluation board where I can test these parameters?

    thnanks

  • 0 in reply to pinhas rosenfelder
    TI__Mastermind 20645 points

    Hello Pinhas,

    For evaluating the SN74AUC2G53, we have a couple leadless adapter options in the product page. 

    Thanks,

    Nir