Hi I am using a voltage regulator ams1117 3.3v to provide engouth power to my external module cause arudino 3.3v pin does not supply enough current.
So I bought this: http://www.advanced-monolithic.com/pdf/ds1117.pdf
I want to know if I can input 12v into this chip and have the output of 3.3v? I ask this cause in the datasheet everytime I check the line of "AMS1117-3.3" I see sometimes VIN 4.8V. Can I provide 12v to this chip without destroyin it?
You can, but it will be very hot.
Power dissipated by the device will be (12V - 3.3V) * current.
Say if you had 250mA of current, then (12 - 3.3)V * 0.25A = 2.175W, so good heatsinking is a must.
Any chance you can use a switching regulator instead? They can be 85-95% efficient, vs 27% efficient with the linear regulator and having to deal with all the heat.
Some examples:
http://www.digikey.com/product-search/en/power-supplies-board-mount/dc-dc-converters/4325599?k=murata+oki&pv1525=94&FV=fff40042%2Cfff800df&mnonly=0&newproducts=0&ColumnSort=0&page=1&quantity=0&ptm=0&fid=0&pageSize=25
The 4.8V Vin figure is listed under conditions. Notice how there are two sets of specs given in those cases, one on the same line were 4.8v is specified (that's the spec with 4.8v Vin) and the other on it's own line (that's the spec over the whole operating voltage range).
As CrossRoads noted, linear regulators are hard to keep cool if you're drawing current, and dropping lots of volts across the regulator. If you must start with 12v, consider a switching regulator. They're cheap as dirt on ebay (search dc dc step down converter) - though bulkier than the ones crossroads linked.
The reason you can't run the on board regulators close to what it says in the datasheet for those parts is because there are no heat-sinks on arduino boards. The regulators rely on copper on the PCB to cool, which isn't very much. So they can only operate at a percentage of their potential.
Nice thank you so much. I will use a heat sink 
I just would like to understand better the datasheet: in the sheet, there is a column "Parameter" and in some lines it is written "Line Regulation" and "Load Regulation". What is that?
Also, I see in the diagram they recommend using a pair of resistors with this chip. Why? The capacitor I understand but why using resistor?
Are you using this to power the nrf24l01 only? from your other topic.
http://forum.arduino.cc/index.php?topic=384975.075.0
If so you might be ok without a heatsink as the current draw is quite small. ( average less than 25 ma)
When making a new post about the same problem, the background info is important, or a link to the other thread. Otherwise people might recommend a switching regulator ( not knowing what you need it for). Or a heatsink ( not knowing the current requirements of your project).
I use sot-223 lm117's for my nrf24l01's without heat issues or noise problems.
@alka good to know! Did you use any capacitor with qms1117 and nrf24l01+? Or you connected your nrf24l01 directely to the chip without any capacitor?
Have you used also the PA LNA version of nrf24l01 with ams1117 3.3v? Did it work well?
The pair of resistors you saw was for the adjustable voltage version, where a pair of resistors are used as a voltage divider to set the output voltage.
You must have capacitors at both input and output of a regulator, per the recommendations in the datasheet on capacitor selection.
I used a 10uf cap on the input of the regulator to ground and a 10uf cap on the output to ground. The resistors on the datasheet are normally for the adjustable versions of the chips , not required for the fixed voltage outputs.
I have used the pa version without issue too, The setup i had when using the pa version though was 12v to a lm7805cv 5 volt regualtor for the arduino. I used the 5v output from that as the input to the 3.3v LDO regulator for the nrf24l01.
This is just from experience.. works stable for me.
Edit : look at the datasheet for proper cap values.
@alka man you were very kind! Thank you, I will use the ams1117 to my PA LNA version too
Good to know about the resistor, I didnt know about that. Thank you so much.
Another approach are buck converters. super high efficiency, need no heat sinks, are adjustable and can provide much higher current. I've started using these and the seem to work very well
Hope this helps.
Actually, that link is http://www.amazon.com/gp/product/B00SY37S00.
Remove the cruft when posting links. 
That would be a cool feature.
Some nice forums already auto-linkify urls.
It would be awesome for a forum to be smart enough to strip out most common forms of kruft (though you need to keep nkw param for ebay links, and whatever the other big vendors use for search terms, so you can link to search result pages, so you can't just blindly lop off params).
DrAzzy:
though you need to keep nkw param for ebay links,
Only for searches.
For items, you strip the question mark and everything following.