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Topic: Atmega1284P @ 16MHz with 3.3V? (Read 2 times) previous topic - next topic

CraigKC

I'm wanting to run the 1284P directly from lithium (4.2V peak, 3.7V nominal) with a LDO 3V3 regulator (dropout ~3.4V).  Page 325 of the Atmel datasheet (http://www.atmel.com/Images/doc8059.pdf) shows the speed grades for the chip.  My first question is to ensure I understand the graph correctly.  Since it's linear it seems like a simple cross-multiplication to get the exact speed at a given voltage.  If my understanding/math is correct...

2.7V @ 10MHz (given)
3.4V @ 12.58MHz (calculated for regulator dropout)
3.7V @ 13.7MHz (calculated for lithium nominal)
4.2V @ 15.55MHz (calculated for lithium peak)

The second question is that assuming the above is correct I understand I'll be overclocking a bit at 16MHz, especially as the batteries drain.  Has anyone else done this?  Maybe with a 328P and can let me know if things went well or they had problems?  I feel like I've read that people have done this without any issue but since this is a small-run commercial product I'm working on I don't want it to be unstable.

Any advice here is appreciated -- thanks in advance!

johnwasser


assuming the above is correct I understand I'll be overclocking a bit at 16MHz, especially as the batteries drain.


I'm confused.  Are you running the processor off the 3.3V regulator or directly off the battery?  If you use regulated voltage the battery voltage won't make a difference.
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dhenry

Quote
Has anyone else done this?


Yes, and it is not a problem, unless you are designing for NASA.

Docedison

@ *dhenry*... Don't quit your day job. Nasa?...

Bob
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pico

#4
Jan 05, 2013, 10:35 am Last Edit: Jan 05, 2013, 10:46 am by pico Reason: 1

Has anyone else done this?  Maybe with a 328P and can let me know if things went well or they had problems?  I feel like I've read that people have done this without any issue but since this is a small-run commercial product I'm working on I don't want it to be unstable.

Any advice here is appreciated -- thanks in advance!


The clocking/voltage specs seem to be very conservative. I (and many others) have run atmega and attiny devices at 16MHz with 3.3V, for example, without any observable problems. Indeed, I've never heard or seen *any* report of a problem overclocking these outside of the datasheet specs.

I personally haven't tried running at a lower voltage than 3.3V at 16MHz, so couldn't tell you where the practical cut-off is. There must be limits, though, and although it is possible to disable brown-out reset completely by fuse settings, I wouldn't recommend it -- it could be coincidence, but the only 328p chip that has mysteriously died on me (even HV programming couldn't get a response from it) was one that I had completely disabled BO resets. I now routinely run BO reset at 2.7V for a 3.3V powered device.
 


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