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SN74AUP1G08: Is it okay to apply different voltages to each input?

Chase Jeong
Genius 5250 points
Part Number: SN74AUP1G08
Other Parts Discussed in Thread: SN74LVC1G08, SN74LVC1G99

Hello TI experts,

My customer wants to apply different voltages to each input with SN74AUP1G08.

input B (pin1) : 4.0V

input A (pin2) : 1.8V

VCC : 1.8V

maybe output would be 1.8V when logic is high because VCC is 1.8V.

is it okay for this situation?

I cannot find any recommended maximum input voltage for logic high.

(I can find absolute maximum rating - it is 4.6V - but I think it is not recommended.)

please check this issue. Thanks.

Best regards,

Chase

  • +1
    Guru 267140 points

    You can find the recommended maximum in the VI specification. It's 3.6 V.

    The absolute maximum rating guarantees that the device will not be damaged with a 4 V input. Exceeding a recommended operating condition implies that correct operation is no longer guaranteed, but in this case, I'd estimate that the output is still correct, and that only tpd might be exceeded.

    If you want to be safe, use the SN74LVC1G08.

  • 0 in reply to Clemens Ladisch
    Genius 5250 points

    Dear Clemens,

    Thank you for your support. I will discuss it with my customer.

    Best regards,

    Chase

  • 0 in reply to Clemens Ladisch
    Genius 5250 points

    Dear Clemens,

    I have more questions from my customer.

    1. SN74LVC1G08, which you mentioned, has input voltage from 1.65V to 5.5V. so different input voltage (1.8V and 4.0V) does not matter for my customer.

    please confirm it again.

    2. if the input is already applied (1.8V and 4.0V in this case) and VCC is applied later, does logic high appear right after VCC is applied?

    or some reset status (logic low or pulse or other status) appears even very short time?

    because my customer wants to see the output immediately, not any reset time. please check this issue too.

    Best regards,

    Chase

  • 0 in reply to Chase Jeong
    Guru 267140 points

    1. Correct.

    2. When the supply is below the recommended minimum (1.65 V), correct operation is not guaranteed. Devices with an /OE input (e.g., SN74LVC1G99) can be deactivated during power up.

  • 0 in reply to Clemens Ladisch
    Genius 5250 points

    Dear Clemens,

    Thank you for your support.

    As you know SN74AUP1G08 and SN74LVC1G08 do not have enable pin.

    What would happen under this situation?

    is the output logic high right after applying voltage to VCC? (My customer does not want any delay-even 1us-until the stable high output.)

    please check this issue. Thanks.

    Best regards,

    Chase

  • 0 in reply to Chase Jeong
    Guru 267140 points

    There are no guarantees.