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SN74LVC2G132: sn74lvc2g132

Part Number: SN74LVC2G132
Other Parts Discussed in Thread: CD4098B, CD4047B


I follow the circuit as shown in the following diagram to control the shutdown pin of an LDO with a tactile switch.

Vcc =5Volts. The circuit works as expected BUT I'm facing power consumption about 300uA. 

Note: The voltage levels on the switch terminals switches (as expected) but instead of Vcc 5Volts I measure 4.6Volts.

Can you suggest anything regarding my issue ? 



Image result for toggle switch with nand gates

  • Hi Theodore,

    You should check out this application report: Implications of Slow or Floating CMOS Inputs

    Short version - slow inputs cause problems.

  • Hi Emrys,

    I'm aware of the implication of slow inputs and this doesn't concern me much.

    My problem is with floating inputs that causes some uA more of power consumption. I tried some circuits with level down resistors but I cannot really solve the problem as it is a toggle switch and level on inputs exchanges.



  • Hi Theodore,
    You say that you aren't concerned about slow inputs, and are concerned with floating inputs causing additional power consumption -- however these two issues are one and the same and are thoroughly explained in the document I provided.

    Even Schmitt-trigger inputs such as the ones on the SN74LVC2G132 will have excess current draw when slow or floating inputs are presented to them -- note the delta_Icc spec in the Electrical Characteristics table - it is expected to see up to 500 uA of current at Vcc - 0.6V on just one input (all other inputs at Vcc or GND). This is a consequence of the circuit design and cannot be eliminated (every modern logic device in the world works this way).

    I think you could design this circuit differently, however, to eliminate the power consumption issue, but it might require a few more devices. I could see a method to do it with a latch and monostable multivibrator (edge detect pulse-generator) such as the CD4098B or CD4047B.

    Also, is the 3-18V supply range a stringent requirement? If so, it limits the parts that you have available to use to only the CD4k line of logic (a very old family that isn't optimal for power savings) -- if you could do this at 5V or 3.3V, there's a pretty wide assortment of parts that could do it.