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MSP430FR5869: ADC output full scale

Kz777
Expert 7895 points
Part Number: MSP430FR5869

Hi Champs,

 

We are using VCC:1.9V and set AVCC=1.9V for ADC input.Also, VREF=AVCC setting.

but, output ADC full scalle value didn't up to 1.9V. This value show 1.2V.
We also changed VREF=2.0V with internal REFVSEL to 2.0V. But, still ADC full scade value was 1.2V.

 

.We would like to make sure, If we would like to get 2.0V full scale, we have to set AVCC is more than 2.5V or some punction number. But, our circuit HW restriction, we have to use AVCC= 2.0V.

 

Do you know some this reason ?

 

Regards,

Kz777

  • 0
    TI__Guru* 77821 points
    Hi Kz777,

    Looking at Table 5-32 REF, Built-in Reference in the MSP430FR5869 datasheet www.ti.com/.../msp430fr5869 you can see in the specification for VRef+ that you need a minimum VCC 2.2V to support REFVSEL = 2.0V. So likely at AVcc = 2V you are unable to achieve the 2V Vref+ because this is out of spec.

    However, can you explain what you mean when you say "the value shows 1.2V" - are you saying that the ADC result is some hex value equivalent of 1.2V (so not the full 0xFFF)? Or are you saying you output the VRef on a pin and you only see 1.2V?

    Regards,
    Katie
  • 0 in reply to Katie Pier
    TI__Expert 7895 points
    Hi Katie,
    Thanks for your input. This value is "the ADC result is some hex value equivalent of 1.2V (so not the full 0xFFF)".
    But, my question, customer wouldlike to use VREF =AVCC. This datasheet requirement internal VREF use case. If we us outside VREF (=AVCC), this still need 2.2V for output ADC hex value equivalent of 2.0V ?

    Regards,
    Kaz
  • 0 in reply to Kz777
    TI__Guru* 77821 points
    Hi Kz777,

    Could you please share a code snippet showing all of the relevant code for the ADC so that we can check the setup and reproduce your issue?

    Regards,
    Katie
  • 0 in reply to Katie Pier
    TI__Guru* 77821 points
    Hi Kz777,

    Would you be able to share the code? You can send it offline if needed. Or did you figure out the issue?

    Regards,
    Katie
  • 0 in reply to Katie Pier
    TI__Guru* 77821 points
    Hi kz777,

    I'm going to close the thread due to inactivity but you can always post back if you have an update.

    Regards,
    Katie

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