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SN74AUP1G57: in2 has a small spikes when power up

Frank Xiao
Genius 12055 points
Part Number: SN74AUP1G57

Hi team,

My customer is using the SN74AUP1G57 now, the schematic is below. When they power up, they find the in2 has a small spikes there. I have let them use different V 3.3v standby (V+ first, then IN2 3v3), No spikes there. Could you please help give some explanation about the phenomenon? Thanks.

ln0  P3V3_STBY

ln1 blue

ln2 yellow

Y purple

  • 0
    TI__Genius 16735 points

    Hi Frank,

    Can you please help clarify? When did the spike not occur? What did you change?

    It looks like both IN0 and IN2 are connected to VCC.

    The inputs of the device are high impedance, with a clamp to GND. If there is noise on the GND, that can come out on your IN1 pin (but this would also impact the output of the device).

    What is driving the input when this spike occurs? I believe something external to the device is causing this spike to occur.

    Thanks!

    -Karan

  • 0 in reply to Karan Kotadia
    TI__Genius 12055 points

    Hi Karan,

    As you can see, now the A & C pull up supply is the same as the V+, I just let them separate the two supply. Give the V+ first, then give the A& C. Thanks.

  • 0 in reply to Frank Xiao
    TI__Genius 16735 points

    Hi Frank,

    There is really no way for the input to experience a rise in voltage from the supply ramping up unless your device has become damaged. Have you tried swapping out the part to see if the same issue occurs?

    It is most likely that something else on the IN2 line is causing the glitch when your supply is ramping together with the other two inputs vs separately. Please look over the entire circuitry to check how the supplies could be having an impact on another device causing the glitch on the input of IN2.

    Thanks!

    -Karan