attiny25 AREF below 2.0V

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So the spec sheet says the external reference voltage can only go as low as 2.0V.  Anyone have any idea what exactly happens if it's oh, 1.8V?  Does the ADC do nothing?  Does it just lose precision?  Does the chip explode?

 

Also the table explaining the bits to set to use it mentions "internal reference turned off".  So if I want to us the bandgap reference as the input channel and AREF as the reference is that still fine?

 

Thanks.  

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Flintrock wrote:
So the spec sheet says the external reference voltage can only go as low as 2.0V. Anyone have any idea what exactly happens if it's oh, 1.8V? Does the ADC do nothing? Does it just lose precision? Does the chip explode?

 

Mostly the latter.  ;)  There have been a few threads on your question in the past year or so; try to search them out.  While  perhpaps not your particular model and level, they should be instructive.

 

 

 

 

You can put lipstick on a pig, but it is still a pig.

I've never met a pig I didn't like, as long as you have some salt and pepper.

Last Edited: Sun. Nov 5, 2017 - 02:59 PM
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You can put lipstick on a pig, but it is still a pig.

I've never met a pig I didn't like, as long as you have some salt and pepper.

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I did try a google search of attiny AREF below 2.0V, in google, of course most hits are here, but nothing much clearly related.  Thanks for the link theusch.  So the answer there is the hard limit is 1.6V, and unclear behavior between there and 2.0.  (well for his particular chip, obviously spec is still 2.0).  Appreciate it.  

Last Edited: Sun. Nov 5, 2017 - 10:59 PM
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Flintrock wrote:
So the answer there is the hard limit is 1.6V, and unclear behavior between there and 2.0.

 

What I took from prioor discussions is that the min value for VREF is "real".  At some lower level, ADC results become unreliable/useless.

 

If the datasheet says "2.0", does the AVR drop over dead at 1.987?  Probably not, so one could probably fudge a bit. 

 

I guess that is why different AVR model lines and generations have added more ref options as noted, along with amplification. In practice, VREF limits have seemed more like annoyances than stumbling blocks.

You can put lipstick on a pig, but it is still a pig.

I've never met a pig I didn't like, as long as you have some salt and pepper.

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Yeah, that's what I got.  It could matter how it fails.  It seems to fail the "right" way, and yes, maybe has a little room for fudging it for non-precision requirements.