AVR-Chat

>>> yahoo@barello.net 03/11/2004 2:28:15 pm >>>
>Ok, I checked the data sheet.  I couldn't find anything regarding the
>bandgap reference on the tiny26.  Where is it?

It's under "Electrical Characteristics" - "ADC Characteristics" - "Vint
- Internal Voltage Reference"
It shows 2.3V to 2.7, with 2.56 nominal. That's a +/-5% error over the
full temperature range. That's pretty crap, any $1 voltage reference
will do better.

Dave :)

At 10:48 PM 11/2/2004, David Jones wrote:


> >>> yahoo@barello.net 03/11/2004 2:28:15 pm >>>
> >Ok, I checked the data sheet.  I couldn't find anything regarding the
> >bandgap reference on the tiny26.  Where is it?
>
>It's under "Electrical Characteristics" - "ADC Characteristics" - "Vint
>- Internal Voltage Reference"
>It shows 2.3V to 2.7, with 2.56 nominal. That's a +/-5% error over the
>full temperature range. That's pretty crap, any $1 voltage reference
>will do better.

8 bit resolution is about 0.5%.. :-P

Please re-read my original post on this subject.  I never claimed that the
tiny26 band-gap had high accuracy.  I claimed it had high stability.  Those
are two very different parameters.

Recently, somewhere that I cannot seem to put my finger on..., someone
actually measured the drift of the tiny26 reference and found it to be about
1.1% or so over temperature (-40, 80c) and VCC (3-5v).  For room temperature
applications with regulated supply voltage the stability would be much
better - probably good enough for many applications when calibrated (i.e. a
scale factor stored in eeprom).  In Dave VanHorn's case, even the full temp
range drift would be acceptable for his battery charger, had he calibrated
each unit.

I would like to see an Atmel data sheet characterizing the band-gap
reference, however, Before committing any design to it.  That I cannot seem
to find.

Cheers!

-----Original Message-----
From: David Jones

>>> yahoo@barello.net 03/11/2004 2:28:15 pm >>>
>Ok, I checked the data sheet.  I couldn't find anything regarding the
>bandgap reference on the tiny26.  Where is it?

It's under "Electrical Characteristics" - "ADC Characteristics" - "Vint
- Internal Voltage Reference"
It shows 2.3V to 2.7, with 2.56 nominal. That's a +/-5% error over the
full temperature range. That's pretty crap, any $1 voltage reference
will do better.

Dave :)

>   In Dave VanHorn's case, even the full temp
>range drift would be acceptable for his battery charger, had he calibrated
>each unit.

This is what I wanted to avoid.


>I would like to see an Atmel data sheet characterizing the band-gap
>reference, however, Before committing any design to it.  That I cannot seem
>to find.

There is an internal one, I was read some parameters over the phone on it, 
but we're probably not going to see a copy.