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ADS1259-Q1: Question when using ADS1259-Q1 as single-ended setting

RYO
Intellectual 2000 points
Part Number: ADS1259-Q1
Other Parts Discussed in Thread: ADS1259

Hi all,

Can you answer to the questions below about the settings to use this ADS1259-Q1 as single-ended setting (0-5V).

  • To use full scale bits when setting AVDD=5V and AVSS=0V, how can I set VREFP and VREFN? If VREFP=5V and VREFN=2.5V, is ADS1259-Q1 able to use all 24 bits?
  • What value should I put into FSC register in this case? I think gain is not needed for this and the default would be fine.

Thanks,
RYO

  • 0
    TI__Mastermind 37211 points

    Hi Ryo,

    As you can see from Table 16 in the ADS1259 datasheet, the coding scheme extends from -VREF to +VREF. So if your VREF = 2.5V, then your input signal would need to extend from -2.5V to +2.5V to see the entire full scale range. Since your input signal is 0-5V single-ended, you could bias AINN to 2.5V and apply your 0-5V input signal to AINP. When your input was 0V, the ADC would see a differential voltage of AINP-AINN = 0V - 2.5V = -2.5V, or negative full scale. When your input was 5V, the ADC would see a differential voltage of AINP-AINN = 5V - 2.5V = +2.5V, or positive full scale. This would be one way to use the ADS1259's entire full-scale range given your input signal span.

    To set FSC to the default value (gain correction = 1), Table 12 in the ADS1259 datasheet says to set FSC = 400000h

    Hope this helps you get started with your design!

    -Bryan

  • 0 in reply to Bryan Lizon86
    TI__Intellectual 2000 points

    Hi Bryan,

    Thank you for your reply. I'm talking about the situation when the external VREF is used which are VREFP=5V, VREFN=2.5V, AVDD=5V, and AVSS=0V. Can you tell me the feasibility for measuring the voltage between 0-5V in this configuration?

    Regards,
    RYO

  • 0 in reply to RYO
    TI__Mastermind 37211 points

    Hi RYO,

    As stated in the previous post, using VREFP = 5V and VREFN = 2.5 V provides a differential reference voltage (VREF) of 2.5 V. This should be okay as long as you do not violate the conditions specified in the "Voltage Reference Inputs" section of the Electrical Characteristics table. You are close to the max allowable value for VREFP, which is AVSS+100mV. If your supply voltage droops or your VREFP voltage increases for some reason, then you may be outside of the recommended operating conditions such that datasheet performance is not guaranteed.

    You would still need to bias AINN to 2.5V to use the full-scale range of the ADS1259.

    -Bryan