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'[PIC] fixed voltage reference on 16F884'
2007\11\08@201307 by Bob Blick

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I'm looking for information on the fixed voltage
reference that's in the 16F884 and others. The
datasheet for the part, 41291D.pdf, makes note that I
should consult the electrical specifications section
of the document for the delay before it's valid, and I
imagine other relevant specs, such as the upper and
lower voltage limits of the reference. However, in
typical Microchip style, those specifications are
nowhere to be found("graphs not available"). Of course
this document is marked "preliminary" as are almost
all Microchip documents (until the part is no longer
recommended for new designs, saves having to issue
erratas I suppose).

Does anyone know if there's a document that covers the
fixed voltage reference (0.6 volt) and has any specs
at all about it, even if it's another part number? I
just want somewhere to start before I do my own
environmental tests.

Hate the way Microchip has everything important left
out, especially when it comes to analog stuff, in all
their documents.

Thanks,

Bob

2007\11\08@213759 by Jinx

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> Does anyone know if there's a document that covers the
> fixed voltage reference (0.6 volt) and has any specs
> at all about it

www.microchip.com/Stellent/idcplg?IdcService=SS_GET_PAGE&nodeId=1824&
appnote=en527808

AN1072  Measuring VDD Using the 0.6V Reference

http://ww1.microchip.com/downloads/en/AppNotes/01072A.pdf

Measuring VDD Using the 0.6V Reference s/w

http://ww1.microchip.com/downloads/en/AppNotes/AN1072src.zip

2007\11\08@221559 by Bob Blick

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Jinx wrote:
>> Does anyone know if there's a document that covers the
>> fixed voltage reference (0.6 volt) and has any specs
>> at all about it
>
>
> AN1072  Measuring VDD Using the 0.6V Reference
>
> http://ww1.microchip.com/downloads/en/AppNotes/01072A.pdf

Thanks Jinx!

Well, they are very clear about how although this is representative of
one particular sample, the data sheet must be consulted. (After the part
has been discontinued and a complete data sheet has been issued).

But judging by the representative sample, it's not a very good reference
and I'll treat it accordingly.

Cheerful regards,

Bob

2007\11\09@005524 by David Meiklejohn

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> Does anyone know if there's a document that covers the
> fixed voltage reference (0.6 volt) and has any specs
> at all about it, even if it's another part number? I
> just want somewhere to start before I do my own
> environmental tests.

I guess "even if it's another part number" covers the 16F506 (even though
that's a different core), and the datasheet for that, in table 13-1
"Comparator Specs" gives internal voltage reference: 0.550V min, 0.6V typ,
0.650V max.  I.e. +/-0.05V, or 8.3%.

No figures on temperature or Vdd stability, just the min/max range.

Not high accuracy at all, although my own testing has found it to be
within 1% of 0.6V with Vdd=5V for a sample of 1...  Useful for a
non-demanding application, like warning/shutdown on low alkaline
batteries.

David Meiklejohn
http://www.gooligum.com.au


2007\11\09@095652 by SME

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face
> I guess "even if it's another part number" covers the
> 16F506 (even though
> that's a different core), and the datasheet for that, in
> table 13-1
> "Comparator Specs" gives internal voltage reference:
> 0.550V min, 0.6V typ,
> 0.650V max.  I.e. +/-0.05V, or 8.3%.
>
> No figures on temperature or Vdd stability, just the
> min/max range.
>
> Not high accuracy at all, although my own testing has
> found it to be
> within 1% of 0.6V with Vdd=5V for a sample of 1...  Useful
> for a
> non-demanding application, like warning/shutdown on low
> alkaline
> batteries.


If it's based on a bandgap reference as it probably is then
the stability is liable to be reasonable even if the initial
value is not especially constant between processors.


       Russell

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