# What a weird operating range, 2.97V to 3.63V

I've seen several microcontrollers rated to operate from 2.97V to 3.63V. Others I've seen rated from 3V to 3.6V.

What's with the extra 30mV on either end of the scale? It doesn't seem like it would make any difference, but maybe I'm missing something.

• It's a ridiculous spec that only shows that whoever wrote it doesn't understand beans about numbers. – stevenvh Jul 17 '11 at 16:06

So that is 3V (with a 1% tolerance) to 3.6V (again with approx 1% tolerance)

OR

as Thomas O commented 3.3V +/- 10%

• This makes the overall range ±10%. – Thomas O Oct 27 '10 at 13:52
• No, 3.6 * 101% = 3.636, which rounds to 3.64. It's 3.3 ±10%, and not 3.0 - 1% to 3.6+1%. The two aren't equivalent. – Kevin Vermeer Oct 27 '10 at 14:31
• @reem You can't round up maximum ratings, you will have to round it down. – Jader Dias Oct 29 '10 at 1:46

I am assuming that is just a precaution or tolerance. Stating that if you run it at 3V its not the bottom of the scale, and you are safe there.

• I think this is false. You would need >30mV ripple to be 'safe', and, as Thomas O pointed out, it's just 3.3V ±10% (a contrived number). 'Safe' would be 3.3V, running near maxes or mins is dangerous. – Kevin Vermeer Oct 27 '10 at 14:33