Could someone suggest the proper heatsink for this regulator:
http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=LM1084IT-5.0-ND

5V fixed voltage regulator, up to 5A operation.

Much appreciated.

 

Hello,

The size of the heatsink depends on the power to be dissipated.
The heat dissipated is ((Vin-Vout) * Iout ) watts.

Here is a page that will tell you a lot about heatsinks:
http://sound.westhost.com/heatsinks.htm

And here is a page on making the heatsink yourself:
http://sound.westhost.com/articles/diy-heatsink.htm

Bertus

 

To calculate the heatsink, you need to know the maximum power dissipation, calculated as bertus told you, the maximum junction temperature (from datasheet, in this case 125°C), the thermal resistance of the device (from datasheet, in this case it seems to be 2.7°C/W), and the maximum ambient temperature you want it to be able to handle (for example: 40°C, if you want it to work on a hot summer at normal ambient temperatures. It could be even more if the place where it's put is hotter).
If you use some thermal interface matherial, you also need to know it's thermal resistance.

The datasheet explains the thermal calculations, under "Thermal considerations" in page 8.