I'm using Arduino Pro Micro (5v version) in one of my project for my car. The car's 12V +ve connected to RAW input of ProMicro and everything seems to work perfectly until I crank the ignition of my car. Here's what actually happened, my circuit works perfectly fine when car's ignition is in ON state. However, as soon as I started my car the voltage dropped from 12v to between 9-10volt and the LG33 (SMD voltage regulator) burned out. Now, I want a good solution as what should I do now? I have already LM2596 DC 3A Step-Down regulator. So should I use that to step-down 12v to 5v OR is there anything else I can do which might be a better solution?
What happened was the ignition caused massive spikes on the 12V power. You require an automotive grade regulator that can cope with spikes in excess of around 70V or more.
Your best bet is probably a car USB charger adapter since they are cheap and easy to get hold of.