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karlos
Joined: 03 Apr 2015
Posts: 107
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 Posted: Wed Jun 08, 2016 6:20 am Post subject: using external and internal adc refrence of xmega |
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Hi
I connect the external refrence voltage of 2.5 volt to aref pin of xmega32a4, but i now decide to not using it because of low accuracy of external tl494 that i connected to aref pin.
if i want to use internal 1v refrence,should i disconnect external refrence from aref pin or not?
i check the datasheet and appnotes of xmega, there is a multiplexer that choose the different refrence according to programming, it seems to be no problem, but 1 of my 5 pcb after 1 week working this way fail and return a constant value.i want to sure that problem is not related to connecting external refrence to aref pin and using internal refrence.
thanks
(BASCOM-AVR version : 2.0.7.8 ) |
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Meister
Joined: 27 May 2010
Posts: 319
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| Posted: Wed Jun 08, 2016 7:38 am Post subject: |
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I remember to have read that external Aref source works against internal Ref if set, potentially destroying the chip.
Better not do that.
Regards, Meister |
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MWS
Joined: 22 Aug 2009
Posts: 2262
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| Posted: Wed Jun 08, 2016 8:09 am Post subject: |
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| Meister wrote: | | I remember to have read that external Aref source works against internal Ref if set, potentially destroying the chip. |
If you remember to have read something, now would be a good occasion to quote this reading and prove you're not wrong.
As if it was the data sheet you've read, this kind of "hearsay knowledge" isn't funded, in contrary it is contradicted by the typical XMega ADC schema, where any of the ref-sources is an input of the reference voltage multiplexer.
Much different it is with the non-X types, as there ARef is hardwired to the output of the reference voltage multiplexer, thus short circuiting it, if the multiplexer is set to anything else than "off". |
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Evert :-)
Joined: 18 Feb 2005
Posts: 2156
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| Posted: Wed Jun 08, 2016 9:37 am Post subject: |
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Aref REFA is connected to PA0,
Aref REFB is connected to PB0.
If you don't make these pins as output I don't see any problem. If you make them output it can destroy the tl494 maybe by shorting the ref output from the tl494.
Are you shure your using tl494, it's a pwm controler?
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karlos
Joined: 03 Apr 2015
Posts: 107
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| Posted: Wed Jun 08, 2016 12:28 pm Post subject: |
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thank you for all respones,
@Evert: i write wrong, i use tl431 as refrence.
no, i dont set the arfef pins output.
now i want to change atxmega32 and check it for 2 weeks.also i check all other things,all seems to be ok. if the problem repeated, i will write here for other users to notice it in future designs. but as Evert and MWS wite here, it seems to be no problem according to datasheets for Xmega series. if any one has practical experiments please write it here.
Regards |
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