What is the difference between IO protection diodes and Power supplly clamps?

[nirmit.patel]

We use IO protection diodes and clamps for ESD protection. All are basically different types of diodes.

Can anyone explain me about the basic difference between ESD protection diodes and Power supply clamps?

What are the rules which drive the placement of these diodes?

 

[mikersia]

ESD protection strategy should solve task of whole system protection. You have to provide way to bypass ESD current through a predetermined structures. Typically for that pair of diodes are added between each IO and power railes, plus (!) power supply clamp to provide discharge path for any combination of ESD event. Power supply clamp can be built in different styles. For example from zener diode with Vbv>Vdd. Differently from protection diodes of IO, it will work in breakdown mode in some of ESD events, and it's construction could be different from IO protection diodes.
Placement of diodes are typically following,- protection diodes are placed near IO pads, power supply clamps are placed into supply IOs. Better to have a distributed power supply clamps, providing low resistive ESD path for any combination of stressed pins.

 

[nirmit.patel]

Thanks Mikersia...