I think your looking for a low dropout regulator, but if it needs exactly 3v and you have a 3v battery, you'll actually need a small switch mode boost convertor (there are some chips for this). The convertor will supply the constant 3v as the battery drops down to 2v etc.
The only boost converter I have experience with is the MAX1674. Boosts anything as low as 0.7v up to 3.3v. I can run a whole project off a single AA battery.
Of course that doesn't help you if 3.3v is too much voltage for you. I'm assuming there must be similar parts for 3.0v if you look around.
Otherwise, to echo the above post, a regulator is not what you want.
Actually, I just realized, the direct settings for the MAX1764 are 3.3v and 5v, but the output is adjustable from 2.0v to 5.5v. You'd have to check the datasheet to see how to do it. I think you need to create a reference voltage with a voltage divider.
The only problem is that the MAX1764 only comes in a tiny SOP SMD package. So that might rule it out as an option for many people.
i have studied my ckt requirement, battery 3 V output with (- 2.8 to + 3.2) is Ok for my circuit. To try with MAX1674, i need a circuit. Could you post it.
Dirty lude - Your two posts mentions, one as MAX1674 and the other as or 1764 which is correct.
It would have taken less time to google search max1674 and max1764 and found your answer than it did to type your message.
It is in fact the MAX1674. The datasheet is available on the Maxim website www.maxim-ic.com and gives you all the information you need to know about how to get what you want from the chip. I will let you know that a 22uh inductor or higher is required.
It looks like Digikey only has the MAX1676 in stock, which is similar, but with added features. They are both listed as over $5.00, but I could swear I got mine cheaper than that.
I stress though, that this IC is very tiny, and unless you have a PCB, maybe impossible to work with. Here is a project that I used this IC. The max1674 is the top left IC. The last picture is the clearest. This is a 3.3v circuit and the max1674 runs the whole thing off of a single AA battery right now, though I will change it to 2 AA batteries, since I have room in the project box.
**broken link removed**
There maybe similar alternative IC's out there that are cheaper. Usually ST makes some nice alternative parts.