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You could use a TVS diode for this type of thing (and any over voltage on the input.) Earlier this week I was helpfully pointed at one of these ESD diodes which is specifically designed for the purpose and cheap:
Actually, having now seen your circuit, I don't think it's suitable. What you want is a TVS diode with a suitable breakdown and clamping voltage - possibly bi-directional depending on the source of the Vin DC. You would need to size for the maximum Vin you supply. You say 14V and 28V and the LM2596 can take a maximum 40V on Vin (you should probably consider the voltage of Cin as well.) So you want a reverse standoff voltage >28V (actually, > pk-pk voltage on that input so it doesn't clip) and a breakdown voltage and a clamping voltage that is as high as you would want to go, definitely < 40V and probably something like 33V but it depends on your design. The datasheet gives a pulse current rating but also, usually, a formula for calculating at other surge voltages. Also check the ESD rating in the TVS datasheet.
If you aren't sure what a TVS is or how it works or how to choose an appropriate one, it's worth googling. They aren't complicated and there is loads of information out there that is easy to understand.
How do you know that it is ESD that is damaging the LM2596 ?
It should be OK with a maximum supply voltage (pulse not continuous) of 45V.
You need to investigate that this is really the problem.
Things to check,
is the LM2596 a genuine TI part ?
what is the maximum input voltage ?
Are there any load side problems ?
If these are OK you could try putting a transorb across the input power supply
(for example ST 1.5KE33A/CA)
The problem is that the margin between clamping voltage and operating voltage is large
for this kind of device and the part I have suggested won't clamp much current (33A) at 45V.
If you used a 1.5KE30A/CA there is a risk it will conduct a bit at 28V but it would clamp a lot
more current at 45V.
I am using 14V and 28Volts battery and connecting it to the Buck converter. Due to ESD the Buck converter IC 2596 is getting damaged. So kindly provide me solution to prevent it by ESD.
Can i use 1n4148 at the input of the Buck converter IC2596 or Parallel to the battery IN.