Hi, I am tryint to power my arduino pro mini using a 3.5 battery pack in the RAW pin. Of course it will not work, so I was wondering if you know any step up AMS family chip that I can use to step up to 12V? Or maybe 7v?
I like the AMS chips cause I already use the AMS1117 and it's very easy. Any solution guys? It does not need to be well regulated cause I am gonna use the output of this converter in the RAW pin of arduino pro mini.
Google "Boost Regulator" and/or "Boost Convertor".
You need to read up on the pro mini. There is no reason to boost voltage that far over what the board runs at (if it was even possible while still having usable current).
Is there any "diy" easy way to boost a voltage from 3.5 to 5 with really small current which I read is the minimm to rum arduino pro mini from RAW? Isnt there some "hack" which I can use? I will draw only small current to power my mini, cant I do any hack without boost converters?
Depends on your definition of "really small current" 
- that can be from microamps (or less) up to amps etc. The best answer will be probably a simple (cheap these days) boost converter. If you want simple DIY, and it really is a low current, you could search on "charge pump" for example as one way.
@gpsmikey GREAT SUGGESTION, I will give it a try to capacitors with the "charge pump" 
8 MHz Promini will run just fine with 3.5 battery pack on the VCC pin, bypassing the regulator. No boost needed.
Or use a www.Pololu.com boost regulator which will make 5V from a single battery down to 0.5V and provide 5V until the battery has nothing left to give.