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ADS8343 - Help on wiring up

Aditya Gaddam
Intellectual 850 points
Other Parts Discussed in Thread: ADS8343, ADS8342

Hi,

I am trying to use an ADS8343 ADC. I am going through the datasheet to figure out if this does what I need. I am looking for something that measure voltages between -2.5 and +2.5.

So far I think this chip will do it. But the way the COM and VREF pins are described is a little confusing. If I want my input ranges to be between -2.5 and +2.5, would I connect COM to 0V or VREF? The datasheet says COM should be connected to VREF, but then the graph afterwards shows VREF changing across 2.5V instead of 0V. 

Any clarification would be appreciated.

Thanks,

Aditya

  • 0
    TI__Mastermind 43915 points

    Aditya,

    There are two things that need to be done in order to use this part with an input range of -2.5V to+2.5V. First, you would want to short the COM pin and VREF pin together and make sure that they are connected to a clean, stable 2.5 V reference source. Secondly, the inputs need to be offset by 2.5V, using an opamp, so that the actual voltage input to the ADC ranges from 0 - 5 volts with a 2.5V COM. When the converter runs in single ended mode, it will reference the input signal to the COM pin. See Figure 2 on page 10. The ADS8343 is a single supply ADC and cannot be directly input with a negative voltage. 

    We recommend that the opamp that is used to offset the input signals by 2.5V is bipolar. This will avoid problems at the opamp rails.

     

    Regards,

    Tony Calabria

  • 0 in reply to Tony Calabria
    Intellectual 850 points

    Hi,

    Thanks for the information, so this isn't really bi-polar? What about ones like ADS8342. The datasheet clearly states +- 2.5 V on the 1st page. In this case I would do:

    1. Connect COM (44) to GND

    2. Connect REFIN(41) = 2.5V

    3. Connect +AVDD and +DVDD to 5V and -AVDD and -DVDD to -5V

    4. Connect REFGND(42) to the GND from 2.

    And then the AIN0-AIN3 pins should just take any signal between -2.5 and +2.5 right?

    Thanks,

    Aditya

  • 0 in reply to Aditya Gaddam
    TI__Mastermind 43915 points

    Aditya,

    That configuration for the ADS8342 would work. The ADS8342 has True Bipolar inputs that would allow for a input range from +2.5 to -2.5V range. Short the Common pin to ground, similar to the setup shown in Figure 1. Keep in mind that the ADS8342 is a parallel output part.

    The ADS8343 has bipolar inputs relative to Vcom (which would need to be set to 2.5V). However the inputs would need to be offset by 2.5V.

    Regards,

    Tony