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### Topic: Do all ICs need regulated voltage?IC data sheet tutorial (Read 2204 times)previous topic - next topic

#### Grumpy_Mike

#15
##### Nov 01, 2011, 10:06 am
Quote
Hmm, so let's take an example.  ATMEGA328P-PU running on 3 AA's and no regulator.  Is there something in the data sheet which advises against this?

An AA battery gives you 1.5V so normally you have 4.5V but when they are very fresh you might get 1.8V from them so that will be 5.4V.
Now look in the data sheet at section 28, and see the absolute maximum operating voltage. This is the voltage you must not exceed. It says 6V so you are OK. Now a battery running down might go to 1.2V so this would give you 3.6V to work from.
Section 28.2 shows you the recommended operating range 1.8V to 5.5V so again from that point of view you fine.
However, section 28.3 shows you that the maximum speed of the clock is related to supply voltage, so you then have to plug in your systems clock frequency and see if it will run at the range of voltages you want. It looks like this is the limiting factor for your design decision of using three AA batteries.

#### maniacbug

#16
##### Nov 02, 2011, 07:09 pm

Quote
Hmm, so let's take an example.  ATMEGA328P-PU running on 3 AA's and no regulator.  Is there something in the data sheet which advises against this?

An AA battery gives you 1.5V so normally you have 4.5V but when they are very fresh you might get 1.8V from them so that will be 5.4V.

...

However, section 28.3 shows you that the maximum speed of the clock is related to supply voltage, so you then have to plug in your systems clock frequency and see if it will run at the range of voltages you want. It looks like this is the limiting factor for your design decision of using three AA batteries.

Thanks...  Yeah, I have measured this extensively, and thought I had everything figured out.  But then I saw this quote, "The majority of IC's need a stable powersource to function properly...Read the data sheet" So I wanted to make sure I didn't miss something, because AA's didn't exactly seem like a 'stable' power source:

Most of my use now is 2xAA's, and it looks like 8MHz is the sweet spot for 2.4V.  Although in my test above, the unit was still operating fine at 1.8V with an 8MHz crystal before the BOD kicked in.

#### Grumpy_Mike

#17
##### Nov 02, 2011, 07:18 pm
Nice graph although the title should say "Voltage" not "Capacity"

Quote
"The majority of IC's need a stable powersource to function properly.

I think that context was about regulated wall wart type supplies. Batteries are stable over the short term, it is just the long term where they drop off. Batteries are like us they are always going to die, it is best to make sure they do it with dignity.

#### maniacbug

#18
##### Nov 02, 2011, 11:28 pm

Nice graph although the title should say "Voltage" not "Capacity"

Thanks.  Indeed, I suppose that is true.  My goal was to measure capacity, so the answer was 13mA * 158h = 2054mAh, not quite the 2300mAh the batteries were rated at.

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