When you are trying to protect a single-ended signal, how do you choose whether to use a TVS, clamp the signal to the rails, or clamp the signal and put a TVS on the rail?
Using a TVS can help prevent backdrive (feeding voltage into the rails of one circuit through the positive clamp), but chances are that a digital IC will have internal clamps anyways, so this might not really help. I also guess that a TVS might take less PCB real estate.
Using a clamp seems like it would be more effective at limiting the peak clamping voltage than a TVS. Also, I would imagine that with ESD, the current pumped into the rail wouldn't cause too much of a voltage change.
How do you choose whether to clamp or use a TVS?
[EDIT] One of the answers motivated me to do some more research. I did some simple SPICE simulations, and it seems that the idea is to use steering diodes (clamps) on signal lines that can't handle capacitance, and to steer the transient/ESD into a location that is more able to deal with the energy (e.g., a voltage rail). A voltage rail has enough capacitance to lessen the voltage rise, and a TVS on the rail prevents the rise even moreso.
Of course, there are many more considerations such as bidirectional, ground level differences, speed, etc. but for my low speed circuit this should be enough.
