Post by thread:[PIC:] PIC internal voltage references

Rant about useless internal voltage references. I originally titled this :Useless internal voltage references" but decided to change it. I'm interested in using a processor with (at least) 10 bit analog to digital converter accuracy. Most with internal A/D have band gap references. These have broad nominal voltage specs compared with the accuracy of the converter. eg 1.11 / 1.23 / 1.34 min/typical/max or about +_/- 10%. OK - maybe we can calibrate this initially. How good is it over temperature and voltage. Let's check the data sheet. Nope. No information whatsoever. It's hardly worth providing a +/- 10% reference with absolutely no information on its characteristics. One may well be better off dividing down and smoothing Vdd ! Looks like an external reference is liable to be essential. OK, I knew that anyway, but you'd think you'd get some help from the makers. What are other people doing? Are there a whole world of people out there using 10 bit A/Ds with a 10% uncharacterised reference ? ;-) Russell McMahon -- http://www.piclist.com hint: To leave the PICList spam_OUTpiclist-unsubscribe-requestTakeThisOuTmitvma.mit.edu

> Looks like an external reference is liable to be essential. > OK, I knew that > anyway, but you'd think you'd get some help from the makers. > > What are other people doing? > Are there a whole world of people out there using 10 bit A/Ds > with a 10% > uncharacterised reference ? ;-) 1. for a real voltage input with an accuracy beyond the (likely 7805-derived) +5V an external reference is unavoidable 2. in a lot of cases the input derives from a voltage divider, so the accuracy of the reference cancels out (but some smoothing might still be needed) 3. when I need both A/D input and D/A output I look for a D/A with a good internal reference. Wouter van Ooijen -- ------------------------------------------- Van Ooijen Technische Informatica: http://www.voti.nl consultancy, development, PICmicro products -- http://www.piclist.com hint: To leave the PICList .....piclist-unsubscribe-requestKILLspam@spam@mitvma.mit.edu

-----Original Message----- From: Russell McMahon [apptechKILLspamPARADISE.NET.NZ] Sent: 03 October 2003 12:39 To: .....PICLISTKILLspam.....MITVMA.MIT.EDU Subject: [PIC:] PIC internal voltage references Rant about useless internal voltage references. I originally titled this :Useless internal voltage references" but decided to change it. I'm interested in using a processor with (at least) 10 bit analog to digital converter accuracy. Most with internal A/D have band gap references. These have broad nominal voltage specs compared with the accuracy of the converter. eg 1.11 / 1.23 / 1.34 min/typical/max or about +_/- 10%. OK - maybe we can calibrate this initially. How good is it over temperature and voltage. Let's check the data sheet. Nope. No information whatsoever. It's hardly worth providing a +/- 10% reference with absolutely no information on its characteristics. One may well be better off dividing down and smoothing Vdd ! Looks like an external reference is liable to be essential. OK, I knew that anyway, but you'd think you'd get some help from the makers. What are other people doing? Are there a whole world of people out there using 10 bit A/Ds with a 10% uncharacterised reference ? ;-) I always use precision low tempco references from Maxim etc. I think the big problem is the process used to make digital circuits is not great for precision analog. Mike ======================================================================= This e-mail is intended for the person it is addressed to only. The information contained in it may be confidential and/or protected by law. If you are not the intended recipient of this message, you must not make any use of this information, or copy or show it to any person. Please contact us immediately to tell us that you have received this e-mail, and return the original to us. Any use, forwarding, printing or copying of this message is strictly prohibited. No part of this message can be considered a request for goods or services. ======================================================================= Any questions about Bookham's E-Mail service should be directed to EraseMEpostmasterspam_OUTTakeThisOuTbookham.com. -- http://www.piclist.com hint: To leave the PICList piclist-unsubscribe-requestspam_OUTmitvma.mit.edu

I've been using TI's REF30xx references. Sources 50 mA, provides < .2% accuracy and is available in several voltages. Unfortunately, it only comes in SOT-23 package. Otherwise, I like it. Mike H. {Quote hidden}>Rant about useless internal voltage references. > >I originally titled this :Useless internal voltage references" but decided >to change it. > >I'm interested in using a processor with (at least) 10 bit analog to >digital >converter accuracy. >Most with internal A/D have band gap references. These have broad nominal >voltage specs compared with the accuracy of the converter. eg 1.11 / 1.23 / >1.34 min/typical/max or about +_/- 10%. OK - maybe we can calibrate this >initially. How good is it over temperature and voltage. Let's check the >data >sheet. Nope. No information whatsoever. It's hardly worth providing a +/- >10% reference with absolutely no information on its characteristics. One >may >well be better off dividing down and smoothing Vdd ! > >Looks like an external reference is liable to be essential. OK, I knew that >anyway, but you'd think you'd get some help from the makers. > >What are other people doing? >Are there a whole world of people out there using 10 bit A/Ds with a 10% >uncharacterised reference ? ;-) > > > > > Russell McMahon > >-- >http://www.piclist.com hint: To leave the PICList >@spam@piclist-unsubscribe-requestKILLspammitvma.mit.edu _________________________________________________________________ Help protect your PC. Get a FREE computer virus scan online from McAfee. http://clinic.mcafee.com/clinic/ibuy/campaign.asp?cid=3963 -- http://www.piclist.com hint: To leave the PICList KILLspampiclist-unsubscribe-requestKILLspammitvma.mit.edu

National LM41xx series in SOT-23 or SOIC if you prefer. microvolts of quiescent current, 0.5% and below intitial accuracy, tempco of 50ppm/c and below etc.etc ... VV >Russell McMahon <RemoveMEapptechTakeThisOuTPARADISE.NET.NZ> wrote: >What are other people doing? >Are there a whole world of people out there using 10 bit A/Ds with a 10% >uncharacterised reference ? ;-) --------------------------------- Do you Yahoo!? The New Yahoo! Shopping - with improved product search -- http://www.piclist.com hint: To leave the PICList spamBeGonepiclist-unsubscribe-requestspamBeGonemitvma.mit.edu