TMS320F28034: ADC offsets by temperature

Hang Yang

Part Number: TMS320F28034

Tool/software:

Hi experts,

My customer is testing ADC's consistency at different temperate. The datasheet says the temperature coefficient is -50/-20 ppm/C

When the temperature difference is 50C, the ADC difference should be 50ppm/C * 50 = 2.5/1000.

However, my customer measured a 1.95 V reference using ADC under a 50C temperature difference, and observed a 20 ADC counts different, which 20/4096 = 5/1000, twice the expected value.

Is any explanation for this observation? Is there any method to decrease the difference caused by temperature?

Regards,

Hang.

over 1 year ago

0 Benjamin Collier over 1 year ago

TI__Mastermind 36526 points

Hang,

Hang Yang said:
Is any explanation for this observation? Is there any method to decrease the difference caused by temperature?

We provide a procedure for periodic offset calibration which will improve performance across temperature. Is the customer doing this?

Thanks,

Ben Collier

0 Hang Yang over 1 year ago in reply to Benjamin Collier

TI__Intellectual 2851 points

Hi Ben,

They find it difficult to calibrate ADC periodically since the control loop is non-stop. Is there any way to calibrate ADC without affecting the control loop?

In the meantime, is there any explanation to why the error is twice the expected value?

Regards,

Hang.

0 Benjamin Collier over 1 year ago in reply to Hang Yang

TI__Mastermind 36526 points

Hang,

Hang Yang said:
They find it difficult to calibrate ADC periodically since the control loop is non-stop. Is there any way to calibrate ADC without affecting the control loop?

I don't think so, it requires CPU overhead to do the calibration, and I think that is unavoidable. Is it possible for the customer to do this infrequently?

Hang Yang said:
In the meantime, is there any explanation to why the error is twice the expected value?

What internal voltage reference is the customer using? I have an explanation if they are using 3.3V reference.

Otherwise these are just typical values, and may be different for different devices.

Best Regards,

Ben Collier

0 Hang Yang over 1 year ago in reply to Benjamin Collier

TI__Intellectual 2851 points

Ben,

Benjamin Collier said:
What internal voltage reference is the customer using? I have an explanation if they are using 3.3V reference.

Do you mean VREFHI? They are using VREFHI = 3V.

Regards,

Hang.

0 Benjamin Collier over 1 year ago in reply to Hang Yang

TI__Mastermind 36526 points

Ok, in that case I think we can just say that this is a typical value, and it will differ from device to device.

0 Hang Yang over 1 year ago in reply to Benjamin Collier

TI__Intellectual 2851 points

Ben,

Since the periodic calibration is difficult, is it possible to calibrate it manually using the internal temperature sensor?

Regards,

Hang.

0 Benjamin Collier over 1 year ago in reply to Hang Yang

TI__Mastermind 36526 points

Hi,

Hang Yang said:
Since the periodic calibration is difficult, is it possible to calibrate it manually using the internal temperature sensor?

Do you mean create something like a look-up table based on temperature values?

Best Regards,

Ben Collier

0 Hang Yang over 1 year ago in reply to Benjamin Collier

TI__Intellectual 2851 points

Hi Ben,

Yes, an offset vs temperature LUT.

0 Benjamin Collier over 1 year ago in reply to Hang Yang

TI__Mastermind 36526 points

Hi,

I am out of office until 9/19/24, I will try to get back to you as soon as possible upon my return.

Thank you,

Ben Collier

0 Benjamin Collier over 1 year ago in reply to Benjamin Collier

TI__Mastermind 36526 points

Hang,

Sorry for the delay. This approach sounds possible, but I do not have any examples for how to do it. It would be up to the customer to implement.

Best Regards,

Ben Collier

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TMS320F28034: ADC offsets by temperature