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SN74AHCT14: replacing TC74VHCT14AF

Genius 5785 points
Part Number: SN74AHCT14
Other Parts Discussed in Thread: SN74AUC14, SN74LS14, SN74LVC14A, SN74LVC3G14


I'm considering replacing Toshiba Logic TC74VHCT14AF (SOP package). SN74AHCT14 (NS package) is hit in TI cross reference. I'd like the 5 V (input and) output tolerant functionality. But SN74AHCT14 does not have the function. Please let me know if you have any suggestions.


  • Hello Kazu,

    The SN74AHCT14 device is overvoltage tolerant on the input. It is not overvoltage tolerant on the output, but in looking at the TC74VHCT14 device, it also is not overvoltage tolerant on the outputs.

    Both devices clamp structures look like the image below, so as far as overvoltage tolerance is concerned, these device are equivalent.

    Is this your concern, or am I misinterpreting your question?
    Please let me know if you have additional questions, and I would be happy to help!


  • Hello Michael,

    Thank you for your quick reply. My concern is the following specification of TC74VHCT14AF.

    DC Output Voltage (Vout) : -0.5 ~ 7.0 (Vcc = 0 V)

    I think that SN74AHCT14 does not have this specification. It looks like just Vcc±0.5.

    In our application, the voltage applied to the output terminal of the logic may be 5 V when Vcc = 0.


  • The TC74VHCT14AF has Ioff protection:

    TI's AHC family does not have Ioff protection. If VCC < 5 V, you could use SN74AUC14 or SN74LVC14A. At 5 V, there would be SN74LS14 (with TTL output levels).

  • Clemens is correct,

    This device does not have back drive protection when VCC = GND, so it would not be recommended to exceed VCC on the output at any point because it would turn the device on, then potentially cause bus contention at the output.

    The suggestions clements provided are likely the best, you may also consider the SN74LVC3G14 if you don't need a pin to pin replacement and aren't using all four channels of the existing device.