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SN74LVC2G14: SN74LVC2G14 Current consumption

Michael Larsen59
Prodigy 40 points
Part Number: SN74LVC2G14
Other Parts Discussed in Thread: MSP430G2001

We are using SN74LVC2G14 in a fault handling circuit.

And we use a separate low power, 5V power supply circuit for that.

One of the two schmitt triggers is used to generate a  clock pulse with approximately 10KHz frequency,
we are doing that with a 100K feedback resistor and a 2n2 capacitor, to GND.

Now the point:
The current consumption of this small circuit is approximately 15mA, and we have tried to build the circuit as a mug-up,
with short wires and ceramic 100n decoupling of vcc, and the input of the other schmitt triger connected to GND.

According to the data sheet the current consumption should be around 1mA 

  • 0
    TI__Guru* 96591 points
    Hi Michael,
    The oscillator circuit works because of the hysteresis on the input voltage threshold for the SN74LVC2G14. Unfortunately, that means the input voltage is _always_ between the thresholds of the device. This will always produce excess current - it is a fairly common misconception that because a Schmitt-trigger device can handle slow inputs, it also will have low current with them. In reality (and as you have pointed out), the device will consume a much larger amount of current when operating this way. It is designed to not be damaged, however there is no way around the excessive current draw.

    The datasheet current consumption parameters are specified much closer to the rails for the input (Icc is specified at 5.5V or GND for the input, and ΔIcc is specified at Vcc - 0.6V).
  • 0
    Guru 242930 points

    You could replace that inverter with a real comparator (which needs external components), or a 8.192 kHz oscillator (which is expensive), or a MSP430G2001 that just outputs the divided-down DCO clock (which needs programming).

  • 0 in reply to Clemens Ladisch
    TI__Guru* 96591 points
    All good ideas. Thanks Clemens.
  • 0 in reply to Emrys Maier
    Prodigy 40 points

    Hi Emrys!

    You are right; I did not know that the current consumption was that high when the input is between lower and upper thresholds!
    In most cases the power supply will just supply the needed current, and everything works just fine,
    but in this case I only had 5mA available.

    I think that the solution is to change the power supply.
    Maybe I could redesign the circuit with CMos NAND gate, for example CD4093,
    but then I could run in to other unforeseen problems, and it takes up more space.

    Thank you for fast reply.
    And thank you Clemens for idears