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Topic: Do I need to connect AREF, AVCC and AGND (Read 3 times) previous topic - next topic

Grumpy_Mike

If you do something that the data sheet says you should not then all bets are off. It might function but it won't work. If you have any problems with it you will get no help from anyone.
Why do you think these recommendations are made?
Do you think it is is people being stupid?
Remember Challenger and the O rings? Engineers were ignored then as well.

Osgeld

#6
Aug 22, 2012, 06:33 am Last Edit: Aug 22, 2012, 06:45 am by Osgeld Reason: 1
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If you have any problems with it you will get no help from anyone.


Obviously you have never talked to anyone at Atmel about support

hell our company was buying 40k units of a part a month and got a 2 month EOL notice from them  with a 4000 unit backstock...

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Why do you think these recommendations are made?


CYA

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Do you think it is is people being stupid?


no its being safe, I do the same thing in production. Do you want to have a bad day and deal with 6 months of reaming?

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Remember Challenger and the O rings? Engineers were ignored then as well.


Really?

Ok I am out, basics stand, you want to be 110% sure go by the datasheet, but keep in mind the data sheet was based on a very limited sample during prototyping and may not reflect the exact truth.

I am trying to find out that truth based on my limited testing, but with the MCU pegged at 245ma load under thermal stress running since the first of June, I dont totally buy the datasheets. Though I am not saying that you can count on a part to run at hells kitchen for over 2000 hours with no faults. Do you feel lucky?

For the record I also recently spent a small pile of money on fets that were ESD rated for 35KV on the datasheet, and they puked on themselves at 10KV, 94% (and some change) of the time, in that case the datasheet was worth less than paper one would read or use in the bathroom ... so datasheets are not golden gods 100% of the time

just sayin

Grumpy_Mike

Thermal measurements are only one factor. Have you tested the noise immunity?

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Obviously you have never talked to anyone at Atmel about support

I had extensive contact with Atmel in the past and they were singularly useless. They quoted life on some flash memory as 100,000 our testing showed that this was closer to 80. So much for the data sheet being conservitave.

datatone

The correct treatment of grounds and power supplies is essential if you want your device to work RELIABLY. You might find that things seem to be OK so long as you have got some power getting in, but digital electronics is sensitive to noise on the supply lines (particularly ground).
You should absolutely follow the data sheet instructions with respect to these things, and also ensure that you provide decoupling capacitors close to the supply pins (0.1uF ceramic).
The likely result of not maintaining proper power supply 'hygeine' is that your device works some of the time, but falls over and crashes intermittently.
David

liangw

One thing I noticed where AVCC makes a difference. I bootloaded 8MHz internal 8MHz osc onto an ATMEGA328. I run it bare (without even a pullup on RESET, with only VCC and GND connect on the low pin side), and blink runs fine on 5V, but it fails to run on 3.3V. As you can guess, it ran fine once I connected the GND and AVCC on the high pin number side. I hope this saves time for other who try this :-)

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