Electro Static Discharge (ESD) is one of the most critical things to guard against a mass-produced product. They can easily damage your product, especially in areas where someone can potentially touch it like exposed pads, USB connectors, screens etc. To protect against this issue, you use a Transient Voltage Suppressor(TVS) or ESD diode on the input side of your circuit. TVS diodes and ESD diodes are technically more or less the same as TVS diodes capable of protecting against larger surge currents too. If you are only worried about ESD, then use the smaller ESD diodes.
You connect ESD diodes right at the input(In parallel, across the rest of the input), usually very close to the part which is exposed. There is a common misconception that the ESD diode will absorb all the transient energy just because you put it somewhere. Well, that’s not how it works. ESD diodes help shunt away the high voltage back to the source, hence it’s imperative that you choose a diode that is fast responding and is placed as close to the input as possible so that the energy put in can return back faster thereby protecting circuits downstream. Never use Zener or other types of diodes for this as it’s usually slow to react to the pulse of an ESD.
IEC 61000-4-2 is the testing standard applicable for ESD before releasing your product on the market. Your product will be tested with an ESD gun capable of injecting a voltage of the order of kilovolts.
They are usually of 2 types, Air Discharge(That is when you bring your hand close to a device but not touch it. Think sparks from fingertips due to charge build-up) and Contact discharges(Direct touch). There are different levels from Level 1 to Level 4 increasing the amount of protection your device is ensured against. For example, Level 4 protects against +-15kV(Air Discharge ) and +-8kV(Contact Discharge) There are lots of considerations in choosing diodes and types of them. Can’t fit them on a single post. If there is some interest, will probably do a detailed series later on.