AVR-Chat

--- In AVR-Chat@yahoogroups.com, "Alexandre Guimaraes" <listas@...> 
wrote:
>... simple and cheap zener regulator with
> emitter follower ... Atmega168 with the
> AD converter using the internal 1.1 volts
> reference. As the input voltage range is 
> ... from about 5 volts up to 40 volts ...
> ... get into trouble varying the supply
> at the AVR in the range of 3 to 5 volts.
> ... Would the AD suffer ...

I don't think you could have looked very hard for your references.  On 
the front page of the data sheet, you can read that the ATmega168 will 
operate from 2.7 to 5.5 volts as long as you don't expect to clock 
faster than 10 MHz.  In Figure 28-36 there is a graph of the bandgap 
reference voltage as a function of VCC and temperature.  It seems to 
vary by less than 0.3% over the full range.  This may be characterized 
and not tested, but you will probably be OK for 8-bit accuracy.  On the 
other hand, note that in Table 27-7 the reference voltage is given as 
1.0 V min and 1.2 V max.  So, although the supply voltage variation you 
expect won't mess you up, the variability in the reference might.

Graham.