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CD74ACT139: Using at 4.0V instead of recommended range of 4.5V to 5.5V

stephen connell
Prodigy 40 points
Part Number: CD74ACT139

Since the "T" in the name refers to ACT devices being compatible with legacy TTL devices, which will not be used in this case, my question is :Will this device function properly using a 4.0V supply? All of the surrounding logic is operating at 3.3V so it will never see a voltage greater than that. I have an existing design that uses the 74ACT139 and would like to reduce the supply voltage but avoid changing the component It seems to operate fine when I've tried it. Is there any change to be expected in the switching time?

  • 0
    TI__Guru* 96591 points
    Operating the device outside of the recommended values on the datasheet will void the guaranteed specs on the datasheet - ie we can't guarantee a part operating at 4V will work the way the datasheet says if we spec'd it at 4.5V.

    However -- operating this device at 4V will not damage it (the abs max voltage range is guaranteed from -0.5V to 6V), and most likely you will see performance very close to or within the datasheet specs.

    As for timing expectations -- resistance typically increases across a FET as VDS is decreased, so you would expect timing to be negatively impacted, however I would expect an ~10% change in voltage to result in a pretty minor resistance increase/timing change.
  • 0 in reply to Emrys Maier
    Prodigy 40 points
    Thank you for the rapid response Emrys.