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AREF bypass capacitance on ATMega2560?

J

Joerg

Jan 1, 1970
0
Folks,

What's the usual capacitance? Any stability issues there? I was planning
on using a 1uF X7R ceramic cap on the AREF pin of an ATMega2560, in
order to be able to use its internal bandgap reference. I saw people
using 0.1uF and 0.47uF. The datasheet is silent about stuff like that,
as usual.
 
L

LM

Jan 1, 1970
0
Folks,



What's the usual capacitance? Any stability issues there? I was planning

on using a 1uF X7R ceramic cap on the AREF pin of an ATMega2560, in

order to be able to use its internal bandgap reference. I saw people

using 0.1uF and 0.47uF. The datasheet is silent about stuff like that,

as usual.



--

Regards, Joerg



http://www.analogconsultants.com/

Are you sure the datasheet does not explain it. I have read that data sheetand it explained filtering for minimum noise. I don't remember any detailsbut filtering the ADC supply was there. What about some example schematics.. I am sure I got values somehow (pulled from sleeve?).

Leif
 
J

Joerg

Jan 1, 1970
0
LM said:
Are you sure the datasheet does not explain it. I have read that data
sheet and it explained filtering for minimum noise. I don't remember
any details but filtering the ADC supply was there.


Atmel mentions "a capacitor" but no values. I've parsed it several
times. I could write to them but IME such things take their time and I
wanted to submit to layout preferably tomorrow.

... What about some
example schematics. I am sure I got values somehow (pulled from
sleeve?).

The ones I found had it tied to AVCC.
 
L

LM

Jan 1, 1970
0
Folks,



What's the usual capacitance? Any stability issues there? I was planning

on using a 1uF X7R ceramic cap on the AREF pin of an ATMega2560, in

order to be able to use its internal bandgap reference. I saw people

using 0.1uF and 0.47uF. The datasheet is silent about stuff like that,

as usual.



--

Regards, Joerg



http://www.analogconsultants.com/

Well, I used 100nF there. How I got it I don't remember. I may have appliedsome exact scientific method like making a guess (or picked a piece muesli) and it worked well enough. I don't remember any large problems just therebut Atmel's Datasheets are not perfect. If I now go and look at the datasheet and find the answer then... Are you sure you read it through.
 
L

LM

Jan 1, 1970
0
Folks,



What's the usual capacitance? Any stability issues there? I was planning

on using a 1uF X7R ceramic cap on the AREF pin of an ATMega2560, in

order to be able to use its internal bandgap reference. I saw people

using 0.1uF and 0.47uF. The datasheet is silent about stuff like that,

as usual.



--

Regards, Joerg



http://www.analogconsultants.com/

2560 cpus are used in Arduino cards. They use 100nF there. Allthough I must say I truly hate schemas made with eagle.

A application note seems to use 0.33u. So anything will work.
 
J

Joerg

Jan 1, 1970
0
LM said:
2560 cpus are used in Arduino cards. They use 100nF there. Allthough
I must say I truly hate schemas made with eagle.

I use Eagle all the time. You can make schematics look just like Orcad
or any other.

A application note seems to use 0.33u. So anything will work.


Well, I wanted to be sure so I asked Atmel. Filled out their club
membership application. Surprisingly I received an answer this morning:
They say 100nF. In American that would be 0.1uF :)
 
J

Joerg

Jan 1, 1970
0
Joerg said:
I use Eagle all the time. You can make schematics look just like Orcad
or any other.




Well, I wanted to be sure so I asked Atmel. Filled out their club
membership application. Surprisingly I received an answer this morning:
They say 100nF. In American that would be 0.1uF :)

Forgot to mention, unless I really missed it the Arduino Mega 2560 has
no cap at all there:

http://arduino.cc/en/Main/ArduinoBoardMega2560
 
N

Nico Coesel

Jan 1, 1970
0
Joerg said:
I use Eagle all the time. You can make schematics look just like Orcad
or any other.




Well, I wanted to be sure so I asked Atmel. Filled out their club
membership application. Surprisingly I received an answer this morning:
They say 100nF. In American that would be 0.1uF :)

Now Xerox that diagram 10 times (copy from a copy from a copy...).
That dot will dissapear and make you look stupid because you seem to
have written 01uF. Thats why we use 100nf, 1k5, etc in Europe :)

I hope Atmel didn't lie to you. Atmel likes to be creative with their
specs... I had to put Atmel on my blacklist.
 
J

Joerg

Jan 1, 1970
0
Klaus said:
There is one, 100nF (C3). But any value will do (almost)....

Indeed! Didn't see it. I really hate such netlist style schematics,
better to draw it right at the pin.
 
J

Joerg

Jan 1, 1970
0
Nico said:
Now Xerox that diagram 10 times (copy from a copy from a copy...).
That dot will dissapear and make you look stupid because you seem to
have written 01uF. Thats why we use 100nf, 1k5, etc in Europe :)

We over here in the lands of the Wild West will see the gap and
immediately know there's a dot. That can be a whole 'nother story if
it's casually written as .1uF which I try to avoid.

And who xeroxes anymore these days? I still have a machine in my office
but that's only for legal papers and stuff.

I hope Atmel didn't lie to you. Atmel likes to be creative with their
specs... I had to put Atmel on my blacklist.

So far, in over 25 years, I had only one screw-up with Atmel. One of
their 8051 series uC would not reliably run at full spec'd clock speed
and I had to back off to 75%. They did fess up and apologize though,
something only very few and good companies (such as LTC) do when caught
with a bug.
 
L

LM

Jan 1, 1970
0
Indeed! Didn't see it. I really hate such netlist style schematics,

better to draw it right at the pin.
Now you know why I hate eagle.
 
L

Lasse Langwadt Christensen

Jan 1, 1970
0
We over here in the lands of the Wild West will see the gap and

immediately know there's a dot. That can be a whole 'nother story if

it's casually written as .1uF which I try to avoid.

guess it is just a matter of being brought up with SI units and standard
use

0.1uF and 100nF is the same number of letters

And who xeroxes anymore these days? I still have a machine in my office

but that's only for legal papers and stuff.

even worse they can change numbers:

http://www.dkriesel.com/en/blog/201..._are_switching_written_numbers_when_scanning?
So far, in over 25 years, I had only one screw-up with Atmel. One of

their 8051 series uC would not reliably run at full spec'd clock speed

and I had to back off to 75%. They did fess up and apologize though,

something only very few and good companies (such as LTC) do when caught

with a bug.


-Lasse
 
L

LM

Jan 1, 1970
0
We over here in the lands of the Wild West will see the gap and

immediately know there's a dot. That can be a whole 'nother story if

it's casually written as .1uF which I try to avoid.



And who xeroxes anymore these days? I still have a machine in my office

but that's only for legal papers and stuff.










So far, in over 25 years, I had only one screw-up with Atmel. One of

their 8051 series uC would not reliably run at full spec'd clock speed

and I had to back off to 75%. They did fess up and apologize though,

something only very few and good companies (such as LTC) do when caught

with a bug.



--

Regards, Joerg



http://www.analogconsultants.com/

Atmel does not explain the USB pins of their Mega CPUs very well.
 
J

Joerg

Jan 1, 1970
0
LM said:
Now you know why I hate eagle.


That's not at all Eagle's fault. Any CAD can be used to draw such
chopped up schematics, most that I've see were done in Orcad and Protel
but only because those are very popular programs. After all, you won't
likely hate a particular brand of car just because one crashed into
yours after its driver screwed up :)
 
J

Joerg

Jan 1, 1970
0
Lasse said:
guess it is just a matter of being brought up with SI units and standard
use

0.1uF and 100nF is the same number of letters

Yeah, it's just a custom I guess. Right after my degree I started
working at an American company. It was in Germany but English was spoken
inside the building, units were imperial, and schematics were US-style
with wiggly-line resistors and all that.

Copying machines should never ever second-guess what is on a document.
That is IMO a very bad design and I would never buy a machine like that.

[...]
 
N

Nico Coesel

Jan 1, 1970
0
Joerg said:
We over here in the lands of the Wild West will see the gap and
immediately know there's a dot. That can be a whole 'nother story if
it's casually written as .1uF which I try to avoid.

And who xeroxes anymore these days? I still have a machine in my office
but that's only for legal papers and stuff.



So far, in over 25 years, I had only one screw-up with Atmel. One of
their 8051 series uC would not reliably run at full spec'd clock speed
and I had to back off to 75%. They did fess up and apologize though,
something only very few and good companies (such as LTC) do when caught
with a bug.

I learned the hard way that none of Atmel's parts specced to run at
1.8V will work reliably at 1.8V.
 
J

Joerg

Jan 1, 1970
0
Nico said:
Joerg said:
Nico Coesel wrote:
[...]
So far, in over 25 years, I had only one screw-up with Atmel. One of
their 8051 series uC would not reliably run at full spec'd clock speed
and I had to back off to 75%. They did fess up and apologize though,
something only very few and good companies (such as LTC) do when caught
with a bug.

I learned the hard way that none of Atmel's parts specced to run at
1.8V will work reliably at 1.8V.

Yikes, that does not sound good. What did they say about it?
 
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