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Original question:

TMS320F2800133: internal voltage reference

TMS320F280025C: ADC internal reference accuracy

Chun-Lin Chen
Prodigy 207 points

Part Number: TMS320F280025C

Hi, Gurus:

As I know, If I set ADC working in 3.3V full scale mode, it use 1.65V as reference voltage and 2.5V full scale will use internal 2.5V reference inside.

1. Will external 3.3V power drive the MCU effect the accuracy of ADC?

2. Can you provide the accuracy in percentage of these two voltage reference?

3. If can't, which one is more accurable, 2.5V or 1.65V?

  • +1
    TI__Mastermind 41690 points

    Hi Chun-Lin,

    1.) If the same external 3.3V power that supplies the F280025 is used for external VREFHI, then any noise in the 3.3V supply line as a result of digital switching may couple to the ADC. If an independent VREFHI chip is used, which is generally more accurate than 3.3V LDOs or the internal 2.5V/1.65V reference then it will provide better ADC resolution.

    2.) Both the 1.65V and 2.5V internal references use the same bandgap design, they are just trimmed differently to produce the different voltage levels so accuracy is the same for both internal references.

    3.) For 3.3V internal VREF mode which uses the 1.65V bandgap, the input level is internally reduced to 50%. For example a 3.0V input to the ADC when 3.3V internal VREF is used, is divided by 2 so that 1.5V is actually supplied to the internal ADC channel.  In theory, even the noise riding on the 3.0V input is also reduced by 50%.

    Regards,

    Joseph