ADC accuracy and calibration

Andrew Dai

Other Parts Discussed in Thread: TMS320F28022

I am using the 28022, and the ADC is great at low voltages. At 0.6V, the ADC is off by at most 3 LSB. However, once I get up to 1.6V, the ADC is off by 20 LSB. This is fine, but at 3.0V, the ADC is off by 80+ LSB at 22C. I am using the internal reference, TI supplied offset calibration function, and the Device_cal() call, and although I guess I am technically within TI's accuracy limits, it feels like quite a large amount to be off by for room temperature. Is there something else I can do to increase my accuracy short of using an external reference?

over 14 years ago

0 Brett Larimore over 14 years ago

TI__Guru 57255 points

Andrew,

The first thing I would do is check whether your part is TMX320F28022, TMP320F28022 or TMS320F28022 ? Offset and gain calibration routines on the ADC are usually items that get better once the device gets to TMS status.

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TMX - Experimental device that is not necessarily representative of the final device's electrical specifications
TMP - Final silicon die that conforms to the device's electrical specifications but has not completed quality and reliability verification
TMS - Fully qualified production device
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I'm sure you've seen this, but more information on the calibration routine can be found around page 17 in spruge5 (http://focus.ti.com/lit/ug/spruge5b/spruge5b.pdf).

Thank you,
Brett

0 Andrew Dai over 14 years ago in reply to Brett Larimore

Prodigy 70 points

Hey Brett,

I am indeed using the TMS.

0 tlee over 14 years ago

TI__Guru 62975 points

Andrew,

This is unexpected behavior. Can you contact the local TI sales office to get in touch with direct support?

-Tommy

0 Nicholas Smith57318 over 14 years ago

Prodigy 195 points

Make sure you run the AdcOffsetSelfCal() function after the DeviceCal() function and not before. Also try running the 5 steps in Section 1.8.2 manually instead using AdcOffsetSelfCal(): http://www.ti.com/litv/pdf/spruge5c. Lastly, make sure the gain error is not due to your input anti-aliasing filter.

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ADC accuracy and calibration