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ADS7254: Question regarding sampling a single ended signal.

Keagan Plummer
Prodigy 20 points
Part Number: ADS7254

We are planning to use the ADS7254 in a design that will sample one differential signal and one single ended signal. Would we be able to attach the minus input to GND of the single ended signal? The exact inputs are listed below. 

AVDD=5V

REFIN_A= 3V

AINM_A=GND

AINP_A= 0-3V

Looking at the data sheet, it seems like this would be on the line for Vcm in the the +- Vref range. Am I able to extrapolate the Vcm using the two ranges listed on the datasheet? 

Thanks, 

Keagan P.

  • +1
    TI__Mastermind 22950 points

    Hi Keagan,

    In order to use the single-ended 0-3V signal with this device, you will need to do a SE to DIFF conversion. There is a very tight common-mode voltage specification which is Vref/2 for +/-Vref mode and Vref for 2*Vref mode. 

    Using your signal conditions above, if Vref is 3V then as per the data sheet, your common mode in +/-Vref mode is limited to a minimum of Vref/2 - 0.1V and Vref/2 + 0.1V which would mean 1.4V to 1.6V. If you take have an analog input of 2V on AINP_A and 0V on AINM_A, then your common mode would be (2V + 0V)/2 = 1V and that falls outside of this range. 

    For a SE to DIFF conversion, you can take a look at the following cookbook circuit. 

    Regards,
    Aaron Estrada