This thread has been locked.
If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.
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,
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.
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.
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.