Hi Expert
In datasheet 10.2.1, there mentioned: The high drive will also create fast edges into light loads so routing and load conditions should be considered to prevent ringing.
What does the light load mean here? Is it a kind of uA/mA load? Could you help share more insight for this design requirement? I am not quite clear here.
Thanks!
-Rocky
Hi Rocky,
fast edge into light load may cause ringing, so that layout and load condition need to be considered?
Yes, that is correct.
But as common understanding, the fast edge into heavy load may cause oscillation.
No, that is incorrect. Perhaps you are correct with linear circuits like amplifiers or linear regulators, but in logic heavy loads do not cause oscillation.
As you can see above, the 8 ohm driver (similar to an LVC device operating at 5V) causes much less ringing when connected to a large capacitance (150pF) than with a small capacitance (5pF).
As the capacitance increases, the RLC circuit becomes closer to a critically damped state. Eventually it can become overdamped and have no overshoot at all, such as in this case:
Just as a side note - we would never recommend driving such a large capacitance with a real logic device -- the current output would likely damage the device. This is just to show an example of how larger capacitance affects a logic circuit's output.
