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Part Number: ADS1282
Please explain. How to calibrate gain ads1282 in bipolar mode. I'm not sure how to manage INP and INN pin when gain calibrate and full scale voltage input in bipolar mode.
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The gain calibration requires you to provide an accurate full-scale input signal. For bipolar supplies (+/- 2.5V), your input signal will be biased around a 0-V common mode voltage. Therefore you will want to make INP = +VREF / (4 x PGA) and INN = -VREF / (4 x PGA). (CORRECTION)
Notice that the exact values for INP and INN will depend on your reference voltage and PGA setting. Also, the common-mode voltage doesn't need to be exactly 0V, but the differential voltage (INP - INN) should be very close to VREF / PGA; otherwise you'll end up with a poor calibration result and increased gain error in your measurements.
Does that answer your question?
Best regards,Chris HallApplications Engineer | Precision ADCs
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In reply to Christopher Hall:
In reply to wivach rungshawang:
wivach rungshawangINP = +VREF / (2 x PGA) my Vref is 2.5 and gain 1. so INP = +2.5 / (2 x 1) = 1.25V and INN -1.25V. that correct?
My apologies, I had made a mistake above...
The differential input voltage (INP - INN) should not exceed +/- VREF / (2 x PGA). Or in your orginal case, +/- 1.25V.
Therefore, the difference (INP - INN) should be 1.25V, and the individual voltages on INP and INN should be +/- VREF / (4 x PGA) or +/- 0.625V, respectively.
wivach rungshawangNow I move avdd to 5v and avss to 0v vref is ref6250 and run gain cal with 5.02040V within 103% of full scale but output code is max at 7ffffdbe is eqal 3.18V (gdm8261a 6 1/2 digital multi meter) and now my +VREF = 5.0 and -VREF = 0 so my INP = +2.5V and INN = 0V. that correct?
I'm not quite sure what you mean by "running gain cal with 5.0204V". Is that the REF6250's output voltage? In this case, your input signal should be 2.5-V.
The 103% full-scale tolerance only applies to the input signal and just allows for you to performe gain calibration when your reference voltage is less than 5V.
Now that you've moved to a 5V unipolar supply, you'll also need to increase the input signal's common-mode voltage. You won't be able to connect INN to 0V. I would suggest INP = 3.475V and INN = 0.975V, since this places the common-mode voltage in the center of the "absolute input range" specification.
many thank for your help.
1. In my Bipolar mode when i run gain cal must supply +0.625V to INP and - 0.625V to INN that correct?
2. Sorry for unclear question. In my Unipolar mode i running gain cal with supply 5.0204V to INP and 0V to INN. From your suggestion "You won't be able to connect INN to 0V. I would suggest INP = 3.475V and INN = 0.975V" That my mistake i stop do that.
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