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TMS320F2800157: tms320f280015x ENOBs

Chris Willis
Intellectual 300 points

Part Number: TMS320F2800157

tms320f280015x

Can you elaborate on the ENOB and how this ties into the gain error and also why some input channels are so much lower than others (ex - A6 vs A4).

Also, Best resolution is obtained externally providing analog voltage reference and using 3V and 32pin package?

I am looking at Figures 6-38, 39, 40 from the datasheet)

Thank you
Chris 

  • 0
    TI__Mastermind 40820 points

    Chris,

    ENOB is impacted by noise.  Noise here is primarily coming from coupling on power pins.  If the device is performing tasks, the supply to the CPU and to the peripheral will be noisy.  A4's proximity to the VDDA pin makes it susceptible to coupling noise and this degrades the ENOB quite a bit.  A6 is away from any of the supply pins (VDDA or VDD or VDDIO) so it is less prone to supply coupling noise.

    On the 32-pin package, the only VREF option is external since the VREFHI pin is bonded internally to VDDA, no support for internal VREF.

    Regards,

    Joseph

  • 0 in reply to Joseph Casuga
    Intellectual 300 points

    Can you comment as to (from Figures 6-38 and 39) it shows that the internal analog voltage reference of 3V

    (I am assuming this is a typo since the only options for internal reference VREFHI <not VREG> are 2.5 and 3.3)?

    results in lower ENOB than the internal 2.5V? and much much lower (per Fig 6-38) than using an external voltage reference of 3V?

  • +1 in reply to Chris Willis
    TI__Mastermind 40820 points

    Chris,

    Yes, this is a typo.  I just submitted a ticket to have this corrected.  Internal VREF modes for the 80-pin and 48-pin devices are supported and it is either at 2.5V or 3.3V.  There is a known issue in the internal VREF 3.3V mode having higher noise than the internal VREF 2.5V mode.  This is the reason why the ENOB is worst with internal VREF 3.3V.  Other VREF modes (internal VREF 2.5V and external VREF) have higher ENOB numbers.

    Regards,

    Joseph