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Author Topic: Voltage reference for A/D conversion  (Read 4217 times)
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mris99
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« on: January 21, 2008, 07:48:13 19:48 »

Hi,

I would like sample signal with dsPIC internal ADC.
For dsPIC AD reference I need 5V,
For level conversion I need 2.5V reference.

Could you please suggest me a proper circuit for generating 2.5V,
and exactly the double of 2.5V = 5V reference voltage for the conversion?

I need something like texas part:
TLE2425 precision by-two voltage divider
http://focus.ti.com/lit/ds/symlink/tle2425.pdf

Unfortunatelly it is not so common,
and I could not find it at distributors in my country.

Best regards,
Mris
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madmax
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« Reply #1 on: January 21, 2008, 07:58:34 19:58 »

Hi there, I don't have the document in front of me but I think it was the Sept 2007 issue of Nuts & Volts that had a very nice schematic for a 5.000 volt 0.01% reference. Divide that in half with a couple resistors and your good to go.
-MadMax
« Last Edit: January 21, 2008, 11:50:24 23:50 by madmax » Logged
pickit2
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« Reply #2 on: January 21, 2008, 08:54:30 20:54 »

look up LM136-2.5 plus many more of same votage reference ic's.
you could use two 100k across 5V supply, will get you going, depending on how critical you need it to be.
Also don't the dsPic have an internal 2.5v internal reference.
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caveman508
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« Reply #3 on: January 11, 2009, 06:46:49 18:46 »

We use the TL431 for this purpose.
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tAhm1D
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« Reply #4 on: January 11, 2009, 07:49:23 19:49 »

Hi mris99,
You can try this circuit with TL431 and LM317 and it is very accurate. Hope it will serve your purpose.

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« Reply #5 on: January 11, 2009, 10:53:23 22:53 »

my opinion, you can use mc1503. i used it for my projects and its output stable. you can trust its output. just try Smiley
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tAhm1D
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« Reply #6 on: January 15, 2009, 06:32:18 06:32 »

my opinion, you can use mc1503. i used it for my projects and its output stable. you can trust its output. just try Smiley

Hi kireytir,
I am not aware regarding mc1503. We normally use TL431, which is reliable and very cheap. I tried to download the data sheet from the Net but could not as it is not available in the data sheet search engines I have tried. So, I require help from you. Is it like TL431 packaged both Dip and 3 Pin Type or different? If you kindly post your circuit with mc1503, it will be easier to understand and learn.
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sittichoke
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« Reply #7 on: January 15, 2009, 08:04:08 08:04 »

you can get datasheet from this link Grin
http://www.datasheetarchive.com/pdf-datasheets/Datasheets-6/DSA-112595.html
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MCan
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« Reply #8 on: January 15, 2009, 12:50:44 12:50 »

Hi kireytir,
I am not aware regarding mc1503. We normally use TL431, which is reliable and very cheap. I tried to download the data sheet from the Net but could not as it is not available in the data sheet search engines I have tried. So, I require help from you. Is it like TL431 packaged both Dip and 3 Pin Type or different? If you kindly post your circuit with mc1503, it will be easier to understand and learn.

hi tAhm1D, sittichoke was give link. you could understand all required info of about it.
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tAhm1D
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« Reply #9 on: January 17, 2009, 06:30:34 18:30 »

Hi kireytir,
I have studied the MC1503 and I do not find much difference between this and TL431 in respect to accuracy. But TL431 has the advantage of being available in a 3-pin TO92 package as well as 8-pin DIP package, but MC1503 is only available in 8-pin DIP package. 3-pin TO92 is cheaper and takes less space compared to 8-pin DIP. So, I prefer to use 3-pin TL431.
I appreciate sittichoke for his kind co-operation and help.
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« Reply #10 on: January 20, 2009, 02:52:45 14:52 »

i have just heared this device from you, i ll try using it in my new projects. thanks Smiley
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kayvee
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« Reply #11 on: January 21, 2009, 08:36:34 08:36 »

Don't overlook the possibility of using newer generation low current linear regulators as a reference to generate your 2.5V.  These are commonly available today at 0.4% accuracies.  Of course it depends on the accuracy required in your application, but sometimes it's a quick no fuss way of achieving this.  Alternatively your could power your dsPIC from one of these regulators at 5V and simply divide from there, as pickit2 suggests.

Edit:  Looks like the LM136 is obsolete, at least from National.  LM336 is still available, same thing, different temp range.
« Last Edit: January 21, 2009, 08:45:32 08:45 by kayvee » Logged
ali_asadzadeh
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« Reply #12 on: January 26, 2009, 04:24:17 16:24 »

why not just use the 2.5 ref and make an resistor divider for 5v inputs ?
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« Reply #13 on: January 27, 2009, 05:24:49 17:24 »

its up to u, if u work on dspic u may know about it.
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entekelektronik
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« Reply #14 on: January 27, 2009, 07:23:38 19:23 »

Hi,
You can use LM336-2.5 or LM336-5.0V ref diode. It is good device for ref.Voltages.

 .Adjustable 4V to 6V
• Low temperature coefficient
• Wide operating current of 600 µA to 10 mA
• 0.6 dynamic impedance
• ± 1% initial tolerance available
• Guaranteed temperature stability
• Easily trimmed for minimum temperature drift
• Fast turn-on
• Three lead transistor package

http://www.national.com/mpf/LM/LM336-5.0.html
goog Luck
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ambo
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« Reply #15 on: April 19, 2009, 05:59:09 05:59 »

I use a AD780 for 2.5000V ref.  Initial accuracy up to 0.02%. 

I'm also looking for 5.0V reference with similar accurracy without having to trim them since I don't have precision test equipment.
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