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MSP430F6723A: Regarding VREF terminal input voltage in common mode

Part Number: MSP430F6723A

Hi,

I would like to use a ΔΣ type AD converter(SD24_B) with single-ended input.

The signal level is between 0~3 V. At this time, is it okay to input the same voltage as AVCC to the VREF terminal?

The gain is used at 1 and AVCC is 3.3V and SD24REFS = 0.

Best regards,

  • Hello,

    I see a few issues with what you are proposing:

    1. The maximum value of the VREF terminal is 1.5V. You cannot input the same AVCC voltage (3.3V) to this terminal.

    2. Single ended inputs can be used with the SD24_B peripheral, but you will need to make sure you do not violate the differential input voltage spec:

    Using a gain of 1, the max differential input voltage you can supply is .92V. Inputting a single ended signal level of 3V is not supported.

    Thanks,

    Mitch

  • Hi,

    Thank you for answering.

    Isn't the common mode input voltage range in the table 5-35  the meaning of single-ended input?

    If so, what does it mean?

    best regards,

  • Hello,

    The common mode input voltage is a voltage that is "common" to both the positive and negative terminals of the ADC. Let me give an example of how we can apply these specs:

    The common mode input voltage range has a max value of AVCC (3.3V) given in the datasheet. Using the differential input voltage specs for a gain of 1 (+/- 920mV), this means we could theoretically input 3.3V to one terminal, and 3.3V - 0.92V = 2.38V to the other terminal. A voltage lower than 2.38V will violate the differential input spec. Common mode voltage can be looked at as the average of the 2 voltages applied to both inputs. So for this example, (3.3 + 2.38)/2 = 2.84V is the voltage "common" to both the positive and negative inputs - ie your common mode voltage. Does this make sense?

    Please let me know if you have any other questions!

    Thanks,

    Mitch

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