Bootstrap Tiny15L from 2.4V?

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I'm trying to build a Tiny15 project with two AAA-cells. I plan to use the Tiny15L directly as a miniature boost converter, so that my Vcc can be higher than the battery (mostly for other chips in the project).

After I bought the Tiny15Ls that I need, I decided to use two AAA NiMH cells; they would be OK at full charge (2.8V) but they fall short when partly discharged (2.4V).

Does anyone know if the Tiny15 will start dependably at 2.4V? I don't plan to do anything at 2.4V except get the PWM going. If 2.4V simply isn't going to work, any other ideas?

Space is at a premium here; the whole project is about 40mm long and 20mm wide.

-Mike

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I remember hearing that one of the new chips was spec'd down to 1.8V. If it was designed to run this low, the data sheet ought to say.

So, this is basically a switch-mode controller and you intend to run the chip off the boosted voltage after its running? This might be a little iffy!

Jim

 

Until Black Lives Matter, we do not have "All Lives Matter"!

 

 

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Mike - did you see this topic?

https://www.avrfreaks.net/phpBB2/viewtopic.php?t=23594

Not the same chip, but may help. He's "good" down to 1 volt:

Quote:
i found out that a tiny13 (sample, datestamped 0327) can start on its internal RC oscilator (4.8MHz / at volates as low as 1 volt! and my square-wave test works.

Might want to talk with him...

Please note - this post may not present all information available on a subject.

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Yes, I intend to run the project off the boosted voltage once it's running. I'm expecting the upper MOSFET to serve as ann 'active rectifier' and save me a diode. (I hope it works in reverse; they usually do :shock: )

In my application, once the project is "started" it's intended to stay running. And I intend to always have fresh batteries (2.8V) when "starting". The biggest issue will come if someone plays with the batteries, whether it restarts on 2.4 or not. :?

I guess I'll just have to build some, and if they won't restart on 2.4V I'll have to come up with a plan. :idea:

Other ideas are welcome, any simple circuit that will start on 2.4V and provide an unregulated voltage of 2.7V or higher just to start the AVR. I've considered a CMOS inverter as a charge pump into a "voltage doubler". Any other thoughts? A two-transistor idea would be awesome! I have some transistor pairs in an EMH6 package (smaller than SOT323) that I'm dying to use. :twisted:

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probably cheaper all in all is to use a max1724:

http://www.maxim-ic.com/quick_vi...

although not nearly as fun to build :)

they just take 2 caps and an inductor, and start up as low as .91V... sot23-5 package.

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Sounds like an interesting idea to me. I once used an output from a PIC (bleah) to drive a charge pump to generate a positive voltage for RS232 (the CPU was powered from the negative rail, if you see what I mean), but I'm intrigued by the idea of running the micro itself from the boosted voltage. Be sure to let everybody know how you get on.

Four legs good, two legs bad, three legs stable.

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The Maxim part is very attractive. It's about the same size as the diode I just eliminated and it gives back some precious I/O pins on my Tiny15.

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There are many solutions in the field for supplying blue leds out of 1.5V cells (output ~4V)
One solution can be googled as "joule thief" - contains one transistor. So if required currents are ~< 20 mA or so...?

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How about a processor that can operate at 1.8 volts?. Then you won't need to worry about boosting the supply voltage. e.g. tiny12 has a 1.8 volt version, there are AVR's other too I think. The only draw back is that the max clock speed is much lower e.g. 1.2Mhz for tiny12.

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Tiny12 would be ideal if it had ADCs :D
Tiny13V is even better, but since I already bought my Tiny15's the first thing I'm trying is this. Sorry I should have had results by now, but got busy.
Where I got started on this is that the system has other devices which need regulated 3.3.

The joule theif is clever, but it's unregulated. I would like to use as few additional parts as possible; my idea (if it's practical) needs only an inductor.