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ADS1258 unipolar use

Gary To
Prodigy 240 points
Other Parts Discussed in Thread: ADS1258-EP, ADS1258

I have written this to support@ti but they put me to here. :)

I'm just wonder what are the differences between ADS1258 and ADS1258-EP. 

And the spec sheet indicated that it can use as unipolar operation, what is the full scale input range for the AD? Would it be 2xVref (0-5V)?

Thank you. 

  • 0
    TI__Mastermind 43915 points

    Gary,

    The full scale input range of the ADS1258 is 1.06Vref. This information can be found on page 3 of the data sheet. If you are using a 2.5V reference, then your full scale input range would be 1.06*2.5V = 2.65V. This ADC can be run in unipolar or bipolar mode depending on the supplies and the configuration that you use.

    The ADS1258-EP is an enhanced part to the ADS1258 that is geared towards medical applications. The difference between the two parts is the ADS1258-EP has been rated and gauranteed across a larger temperature range (–55°C to 125°C) compared to the ADS1258 (–40°C to +105°C).

    Regards,

    Tony Calabria

  • 0 in reply to Tony Calabria
    Prodigy 240 points

    My question was what is the full scale range for unipolar mode. All the specs on the data sheet are on bipolar mode. (AVdd: +2.5V, AVss: 0, FSR: +/-1.06Vref, FSR: -2.65 -> 2.65V with 2.5V Vref).

    I just want to know that the specs, to be precise, full scale range of the AD during unipolar mode (AVdd: +5V, AVss; 0). Would it shift to 2*1.06Vref (i.e. FSR: 0-> 5.3V with 2.5 Vref)? 

    And thank you for the info on the EP part. That is very useful. 

  • 0 in reply to Gary To
    TI__Mastermind 43915 points

    Gary,

    When the data sheet says that the part can be run in unipolar operation, it is refering to the power supplies. Setting the power supplies at AVdd = +5V, AVss = 0 will not have an effect on the input range. The input range would be 0 to 2.65 volts (+1.06*Vref) with a 2.5V reference.  Using a 5V reference the input range would be 0 to 5.1V because of the absolute input voltage range constraint that the input cannot be larger than AVDD + 100mV.

    Regards,

    Tony Calabria

  • 0 in reply to Tony Calabria
    Prodigy 240 points

    Thank you Tony.