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By roach
#10101
Hi All, back with more newbie questions:

I'm working on a project with an ATmega128. From the data sheet, this uC has an op. voltage of 4.5 - 5.5 Volts. I will be running this project off of a cell-phone battery, (Nokia BL-4C, here)
which provides in the area of 3.7 volts. Obviously, I will need to do something to step the lower-voltage up to a usable level. Presumeably, there is some basic circuit, that has existed since the dawn of time, to do this. What is it? What am I looking for here? Is is a transformer? A boost converter?

Thanks in advance..
By jasonharper
#10102
A transformer, by itself, won't help you - it requires an AC input.

A boost converter would be a possibility, but it would be a lot simpler to just choose a microcontroller that will directly work from your 3.7V battery - there are plenty of choices available.
By Vraz
#10103
As Jason notes, choosing lower voltage parts is the easiest solution. However, if that is not an option than there are a number of chips which will do this for you. Solutions are typically divided based on whether they require an inductor or not (inductors are usually required for more than 100ma or so). Maxim has several chips for this application and here are a couple of links:

Non-inductor (50ma):
http://www.maxim-ic.com/quick_view2.cfm/qv_pk/1135

Inductor (180ma-550ma):
http://www.maxim-ic.com/quick_view2.cfm/qv_pk/2377
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By roach
#10120
jasonharper wrote:A boost converter would be a possibility, but it would be a lot simpler to just choose a microcontroller that will directly work from your 3.7V battery - there are plenty of choices available.
Amen. Unfortunately (or not?), I'm working with the ATmega128 header board from Sparkfun, and getting a custom version with the 128L is not a possibility...
vraz wrote:Maxim has several chips for this application and here are a couple of links
Thanks Vraz. I've always found Maxim to be a bit... hobbyist-unfriendly (getting samples from them requires some jumping through hoops), but I'll give it a shot. If I understand correctly, I should be able to go with a non-inductor solution, and run the output through the Header board's 5V regulator. I'm not sure how much current the ATmega128 draws. Does that make any sense?
By wheeler
#10132
I completely agree about Maxim/Dallas. Not to mention their chips are expensive once it comes time to pay for them. Check out some of TI's (sample-friendly) offerings, including the TPS6013X, which is designed to do exactly what you want:

http://focus.ti.com/docs/prod/folders/p ... 60130.html