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TMS320F28379D: ADC sensing issue

Suraj Bharate
Prodigy 10 points

Part Number: TMS320F28379D

Tool/software:

I am trying to measure a Voltage at ADC pin 17. I have configured ADC to 12 bits resolution. Internal Vref 3.3V is used for ADC config. I have given 1.5 V to ADC pins directly from a DC source. 1.5 V is clean and I am not using any filter.

I am getting ADC result counts ~ 2050.

2050*3.3 V / 4095 = 1.64V. I am getting this result.    (2^12 -1 = 4095). 

For troubleshooting, I passed adc result (2050 counts) to DAC and measured voltage at DAC ouput pins, I am getting 1.47V.   

I am not understanding what is the exact issue. Why with calculations I am getting 1.65V?

Is it possible that internal voltage Vref is dropping to 3V? If yes then readings make sense. But how to mitigate it?

Thank you.

  • 0
    Prodigy 220 points

    Hi Suraj,

    You're observing a mismatch between expected and measured ADC voltages — likely due to the internal Vref not being exactly 3.3V. If the real Vref is around 3.0V, then your ADC count (2050) would correctly represent 1.5V, which also matches your DAC output (1.47V).

    To work around this, you can apply a correction factor. For example:
    Correction = Actual Voltage / Calculated Voltage = 1.5 / 1.64 ≈ 0.915
    Then, you can scale future readings accordingly.

    However, for more accurate measurements, consider using an external Vref or measuring the real internal Vref voltage and updating your calculations.

    Regards,
    Deep

  • 0 in reply to Deep Patel
    Prodigy 10 points

    Hi Deep,
    Thank you for your response. 

    With 3V input to ADC, I am getting 4095 counts. It seems like internal voltage Vref is 3V. 

    Is there any method by which internal votlage can be measured. As per manual Vref should be 3.3V.

    Thank you,

    Suraj

  • 0 in reply to Suraj Bharate
    Prodigy 220 points

    Hi Suraj,

    You can refer to the following document:
    TMS320F28379D controlCARD R1.3 – SPRUI76C

    Check Table 5-1: Hardware References (SW2).
    It shows that SW2.1 ON enables the internal 3.0 V reference for ADC-A.
    So, if you're getting full-scale at 3.0 V, you're likely using ADC-A with internal reference.

    Let me know if you’re using another ADC module or a custom setup.

    Best Regards,
    Deep

  • 0 in reply to Deep Patel
    Prodigy 10 points

    Thank you Deep.