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Is logic gate output overload protected?

Discussion in 'General Electronics Discussion' started by holex, Aug 25, 2015.

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  1. holex


    Jun 2, 2014
    For example, does the SN74AHC08 output contain overload protection? Datasheet contains that output current is max. 8 mA. What does happen if I connect it to +5V when it would like to be GND? Is is destroy the device or overload protection protect it?
  2. ADRT


    Nov 25, 2014
    There is no overload protection for logic gates. If you short the output it will fail.
  3. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    Jan 21, 2010
    A lot depends on the type of gate. If it's a line driver capable of 80mA then shorting the output will probably exceed the package dissipation limit and result in failure. For a normal gate that may not be the case. However shorting several outputs will probably put you back in a bad place again.

    Another issue is the logic family. TTL can sink more current than it can source, so shorting to the positive supply I'd far worse than sorting to ground.

    CMOS is relatively tolerant unless the gate is a line driver.

    note that the maximum current specified in the datasheet I'd that which allows the output voltage to remain valid. This should not be regarded as a limit to what is possible under conditions where this is not maintained.
  4. holex


    Jun 2, 2014
    Thank you!
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