Post by thread:[PIC] fixed voltage reference on 16F884

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

> 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

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

> 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

> 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