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TMS320F280049C: Is there any difference when design ADC RC filter circuit between F280049 and F28335?

Rayna Wang
Expert 3680 points
Part Number: TMS320F280049C

Hi Expert,

Is there any difference or anything to take care about ADC RC filter circuit designing when transfer from F28335 to F280049?

Thanks!

Best Regards/Rayna

  • 0
    TI__Guru 60865 points

    Hi Rayna,

    The process is the same (see https://training.ti.com/node/1139106), but the input models for the two devices are different, so the designed circuits won't be the same.

    The nominal value of the external Cap is 20 x Ch, so the capacitor for F28004x will be around 10x larger than the cap in the F28335 circuit.

    Since F28335 ADC has a shorter minimum S+H time (because it samples faster), you would also generally need a higher bandwidth op-amp to drive F28335 vs. F28004x.

     

  • 0 in reply to Devin Cottier
    TI__Expert 3680 points

    Hi Devin,

    Thanks for your reply. It's really clear to for the difference.

    My customer using F280049 to replace F28335, however they found the ADC gain error of F280049 is around (-10 ~ +10) comparing with F28335 (-2 ~ +2), with the external 3.3V ADC reference voltage.

    I send the schematic diagram and PCB layout to you offline, could you please help to review them?

    Thanks!

    Rayna

  • 0 in reply to Rayna Wang
    TI__Guru 60865 points

    Hi Rayna,

    Sure, I will review the specific schematic and send feedback.

    Generally, note that the DS gain error specification of F28335 is +/- 30LSBs while F280049 is +/- 5 LSBs

    If the issue is that the voltage of the previous conversion result is affecting the current conversion result, this is a separate error from gain error, sometimes called "Memory Cross-talk".  This error should be close to 0 for properly designed signal conditioning circuitry.  Again, see the linked training from TI precision labs for guidance on how to design appropriate ADC driving circuits.