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How to get 12 bits precision with BurrBrown A/D?

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2000

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hello friends,

Once more I need your help, I'm working with a BurrBrown A/D ADS7812 12bits, bipolar, +5V single supply. I'm having problems with its precision, I'm unable to get the 12 bits precision, actually I'm really far from them. Anybody have already worked with thease A/D's?
Any help is welcome.

regards,

2000
 

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KARLZ

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hi
you should add low pass (LC) filter on analog power line.
thx
 

aNdreiBuuu

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pot a low pass filter too, to AD input, and check the REFERENCE!!!! is designed for 12 bits???? if n -> NO WAY... :smile:
check your PCB and remove the earth current loop, and use guarding architecture...
i miss something? (is much possible...:smile:)

best,
//a
 

2000

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HI friends,

Thanks for the help, the board I'm using is almos the one used for the test board distributed by BurrBrown... the decoupling capacitors, the ground plane, everything... but the precision is poor...
Do you sugest any other A/D like the one I'm using, I mean,12 bits, 200KHz sample, bipolar, serial, single supply, +-3V or +-5V scale??? I'm having difficulties to buy the ADS7812P and I'd like to choose one that would be cheap and easy to find, any sugestions?


2000
 

johnyaya

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what test(s) did you do to determine this? have you looked at input to adc with an o-scope?
 

aNdreiBuuu

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...but ADS7812 work great... anyway if yo want to simplify your design you could use some interesting AD from cr*ystal sem*iconductor ( a division of cirr*us-lo*gic)
best,
//a
 

2000

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sure,

I've put a known DC at its input and whatched it with an osciloscope... it is pure stable DC but the A/D varies its 3 last bits... I've used the decoupling capacitors but it still drifts...

2000
 

aNdreiBuuu

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check the reference circuit this AD workz ok!!
 

KARLZ

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check you power supply. this usually happens when your ps out put is not clean. you have to add inductor in analog supply input in addition to decoupling caps.
thx
 

chief451

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Have you checked the
serial clock feedtrough ?

chief451
 

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