SN74LV123A: Is it OK to input voltage higher than the Vcc?

Part Number: SN74LV123A

Hello team,

I received a question from my customer about behavior of monostable multivibrator logic "SN74LV123A".

Customers are willing to use VCC = 3.3V, and input voltage Vi = 5V(typ) for their application.

Vcc(3.3V) < Vi(typ  5V) < 5.5V

  • Is it OK to apply a input voltage larger than VCC? Or are there any max condition of Vih?

The recommended operating conditions only state high level input voltage as "Vih = VCC x 0.7 V (min)", but there are no max value listed.

Best Regards,

Ryotaro Fukui

  • Hello Fukui-san,

    The recommended operating conditions only state high level input voltage as "Vih = VCC x 0.7 V (min)", but there are no max value listed.

    The recommended input voltage limits are specified separately from the input high state definition:

    Is it OK to apply a input voltage larger than VCC? Or are there any max condition of Vih?

    Yes, the input voltage can be up to 5.5V, independent of VCC.

    VIH is only an indicator of the "high" input state -- so long as your input voltage is above the minimum value (0.7*Vcc), the device will detect that as a 'high' input.

  • Hello Maier-san,

    I understood that Vin could be set independent of VCC as long as it is less than 5.5V.

    I guess this specification makes it possible to set it to "high" with plenty of margin.

    Thank you for your confirmation and I appreciate your prompt response.