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ADC reading problem with 16 bit processor
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temtronic



Joined: 01 Jul 2010
Posts: 7975
Location: Greensville,Ontario

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PostPosted: Mon Jan 25, 2021 9:29 am     Reply with quote

DS70000689d.pdf, page 491, table 33-56, Param AD17....

It's at the bottom of the page, abover the bold NOTE:....


Jay
Ttelmah



Joined: 11 Mar 2010
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PostPosted: Mon Jan 25, 2021 9:31 am     Reply with quote

All ADC's have a minimum impedance needed to feed them. The high speed
ADC's on the PIC33's have a much lower recommended impedance for
the source than the older PIC's. Jay has told you the parameter. AD17.
Minimum recommended source impedance...
MCUprogrammer



Joined: 08 Sep 2020
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PostPosted: Tue Jan 26, 2021 6:56 am     Reply with quote

I am looking for an integrated that I will use for reference voltage that can output 3v. I prefer not to have smd. Is there a product you have used before? LM336 didn't do my job.
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MCUprogrammer
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Ttelmah



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PostPosted: Tue Jan 26, 2021 7:14 am     Reply with quote

Problem is that in 3v, 99% of precision VREF devices will be SMD packaged.
There are a few that come in DIP-8 packages.
I use the REF61xx from TI, but this only comes in a 8pin SMD package.
Look at the AD780. Ground pin8, for 3v. However, big question is what
supply you have available?. This needs 4v minimum for 3v out.
temtronic



Joined: 01 Jul 2010
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Location: Greensville,Ontario

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PostPosted: Tue Jan 26, 2021 8:29 am     Reply with quote

One 'cheat' is to use a chargepump circuit, like I use for running 5V LCD modules on 3V PICs.... to power the precision reference device. It'll add 2 diodes, 2 caps to the PCB ,need 50%+- PWM bit, but should,probably work....
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