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TMS320F28377S: ADC VREFHI For 12-bit mode

user4783191
Prodigy 60 points
Part Number: TMS320F28377S


I just use the 12-bit mode，the ADC VREFHI can connect directly to VDDA, is there any risk (ex: accuracy)?

in 12-bit mode, have any affect?

16-bit mode -> voltage follower

12-bit mode-> ADC VREFHI connect directly to VDDA

Best regards

Ben

  • 0
    TI__Guru 60865 points

    Hi Ben,

    The accuracy that is achieved will depend on the accuracy of whatever is supplying VDDA.  This will typically be much lower than a dedicated VREF IC.

    In addition to the accuracy, connecting VDDA to VREFHI will effectively mean there is no power supply rejection; any noise on the VDDA will go directly to the ADC output.  This could be due to transient current draw from the analog modules, draw from the digital modules if VDDA is ganged with VDDIO, or from the supply of VDDA (especially if it is a switching supply).

  • 0 in reply to Devin Cottier
    Prodigy 60 points

    Hi  Devin

    I have a question

    In TMS28069, I don’t use the voltage follower.

    So I don’t understand, I use the high level DSP with voltage follower.

    In the case

    Is it necessary? Just for upgrade the DSP

    Or TMS28069 have a good ADC accuracy ?

    Regards

    Ben

  • 0 in reply to user4783191
    TI__Guru 60865 points

    Hi Ben,

    It depends on what is driving the VREFHI in your F28069 design.  In general, the ADC VREF will produce high transient current draw during the conversion, so you'll want a large capacitor on the VREFHI pin and a driver that is (1) High bandwidth and (2) able to drive a large capacitive load. 

    If the driver is not high enough bandwidth (the op-amp buffer would typically be selected to have high bandwidth), then the reference driver might not settle the reference between ADCCLK cycles, resulting is conversion issues.  This is more likely to result in distortion (effecting AC spec's like SNR, THD, ENOB, SFDR) than a gain or offset error that would effect accuracy.