TMS320F280049: ADC-to-ADC and channel-to-channel errors

Hello Wayne,

I will look into this and try to get this information to you by tomorrow.

Best regards,

Omer Amir

Hello Wayne,

1. Here are some more details:
   1. Channel-to-Channel Gain Error: This is the worst-case error that occurs between channels within an ADC which happens when the ideal result is compared to the testing characterization at full scale (zero and full scale refer to the point at which the value is measured, zero being when the ADC would read its lowest possible voltage and full being the highest possible reading)
   2. Channel-to-Channel Offset Error: This is the same as the Channel-to-Channel Gain Error, but the comparison happens at zero scale
   3. ADC-to-ADC Gain Error and ADC-to-ADC Offset Error: This is the same as the Channel-to-Channel versions of the errors, except the comparison is now between entire ADCs
   4. ADC-to-ADC Isolation: This is the impact on the result reading when all ADCs and all SOCs/channels are converting simultaneously (with the same sample-and-hold time and trigger simultaneously)
2. Only the offset error (channel-to-channel and ADC-to-ADC) can be calibrated. Can you clarify on what you mean by calibrating the errors together?
3. The datasheet states that all values will be within the same margin of error within the temperature range tested at (if it says -40C to 125C, there should be no deviations within these temperatures beyond the error listed).

Best regards,

Omer Amir

Dear Omer,

"Only the offset error (channel-to-channel and ADC-to-ADC) can be calibrated. Can you clarify on what you mean by calibrating the errors together?"

Questions:

Assuming the user has already called factory OTP trim by Device_cal() in the initialization, the user wants to know if they can calibrate them further.

1. For general gain/offset error, we know the user can use a software based calibration like our app note "TMS320280x and TMS3202801x ADC Calibration" (https://www.ti.com/lit/an/spraad8a/spraad8a.pdf?ts=1673934390939&ref_url=https%253A%252F%252Fwww.ti.com%252Fproduct%252FTMS320F2808)

Here, when you said "Only the offset error (channel-to-channel and ADC-to-ADC) can be calibrated.", it means the user can use a software based method to calibrate like the app note. Or did you mean another?

2. When I said by calibrating the errors together, I meant to use the software based methods like the app note and do it once for all these 3 gain errors and for all these 3 offset errors. Do you think the user can just use same method like the app note to calibrate all these 6 kinds of gain/offset errors including gain/offset, channel-to-channel gain/offset, ADC-to-ADC gain/offset errors in the software code?

Wayne

Hello Wayne,

The app note you're referencing is not for the F28004x device, so I will contact the writer to see if the content is still applicable. I will try to get back to you by tomorrow.

Best regards,

Omer Amir

Hi Wayne,

I confirmed that the calibration used in the app note should be able to be used on the F28004x device, the only thing that needs to change is the safe range calculations based on the gain error min/max in the datasheet for that device, as this is based on device.

Best regards,

Omer Amir

Dear Omer,

Thank you for your update.

But can the software method based on the app note applies for all these 6 kinds of gain/offset errors, or do they only apply for gain/offset errors excluding (channel-to-channel and ADC-to-ADC)?

Hello Wayne,

From my discussion with the writer of the app note, the software method from the app note applies for the gain/offset errors, ADC-to-ADC gain/offset errors, and the ADC isolation, but not the channel-to-channel errors.

Best regards,

Omer Amir