AVR-Chat

Hi, Graham
 
	I would not ask the question without looking at the datasheet ! I
was probably not clear enough about my concerns. The variation on the
bandgap reference is ok to me and the part will definitely operate on the
supply range, but will it operate properly with the power supply varying
dynamically ?

	My real and main concern is to have a power supply that could vary
rapidly from 3 to 5 volts. That is something that I have never done or have
seen done. I did not find any specs about having the supply change
dynamically with the chip running. I was looking for someone to tell me that
I am Nuts trying it or someone that has already tried it with success. It
sounds so much like the tests I make injecting "noise" on the supply lines
that the though about doing it makes me shiver :-(
 
	It would be interesting to be sure that parts with wide voltage
ranges could be used with the supply varying all over the place as long as
the voltage limits are respected. I am not sure that this is true.. 
 
Best regards,
Alexandre Guimaraes


-----Mensagem original-----
De: AVR-Chat@yahoogroups.com [mailto:AVR-Chat@yahoogroups.com] Em nome de
Graham Davies
Enviada em: 13 October 2007 09:59
Para: AVR-Chat@yahoogroups.com
Assunto: [AVR-Chat] Re: Power supply dynamic range.

--- 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.




 
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