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SN74LVC1G08: Overshoot and ringing at the output

Duong Nguyen
Prodigy 90 points
Part Number: SN74LVC1G08

Hi TI Team,

Currently, I have to face the overshoot/undershoot at the output of SN74LVC1G08

There are 2 situations when ringing appears:

1. The long trace is connected to the output. This is caused by mismatch impedance. I can simulate by using IBIS model

2. Short trace is connected to the output. I don't understand why ringing still appears in this case. And I use IBIS simulation but I don't see any abnormal signal

I see light load condition is also a reason why ringing happens. Is it explain why ringing in short trace ?

And in order to reduce ringing, I need to add a serial damping resistor. Is the damping serial resistor always needed?

Do you have any solution to save the cost and space than using damping resistor ?

Thanks,

  • 0
    Guru 285300 points

    LVC devices have very strong outputs and always need proper decoupling. Ensure that there is a capacitor as near as possible to the VCC pin.

    Proper termination is needed for long traces. There are many methods; adding a series resistor at the driver is the simplest and cheapest one.

    What exactly do you mean with "ringing appears"? Did you connect a long oscilloscope probe to the output? You can reduce measurement artifacts by replacing the ground clip with a shorter ground spring.

  • 0 in reply to Clemens Ladisch
    Prodigy 90 points

    Hi Clemens,

    Below is the picture measuring at output of SN74LVC1G08 with a 39Ohm serial resistor, 300mils trace length and no load

    I used a common probe. Because of the measuring point at the bottom, it's hard to use ground clip probe.

  • 0 in reply to Duong Nguyen
    Guru 285300 points

    You did not say anything about the decoupling on your board.

    That waveform is plausible for ringing happening in the ground lead of a standard probe. So far, I do not think that your board has a problem.