Choosing the right ADC for the job

So i'm trying to decide on the correct adc to use in the following application: read the analog output of up to 3 scientific grade sensors with  analog out (offcourse). voltage ranges between 0 and 5V (some are up to 5V others up to 3 etc) and one RTD with accuracy of 0.01°C.

So far i've identified the following requirements:

(multiple adc's allowed)

- 4 differential inputs (3 for generic sensors and one for the RTD)

- Atleast 14bits without noise/errors  (that's the minimum accuracy required to use the sensors at maximum accuracy)

- Built in current excitation source is handy

- speed is of lesser importance, outputrate will be 10Hz max so 50SPS is plenty (incase oversampling is required)

- i'm new to adc circuit design, so 'recommended schematics' in the datasheet are a plus

- can be soldered by hand

The ADC(s) will be connected to a microchip dspic with multiple SPI interfaces.

Based on the above i've so far chosen these ADCs:

AD7176-2 and AD7713

The first one seems a low noise easily interfaced and with few external components ADC.

The second one is harder to interface and more external components but has the current sources and a AIN suited for 4m-20mA interface (which might come in handy).

So I would put one of each on the PCB. (Not 2x AD7713 because of the price and more external components).

Is this a good choice? Or would you recommend other ADC's?

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  • Thanks for the suggestion!

    By combining the schematic of the EVAL-AD7795 and the one in the AD7713 datasheet (for the 4wire RTD on page 24) I ended up with this.

    Regarding the EVAL one, could you tell me what the 0R resistors are for? Or are they just place-holders?

    In the AD7176-2 (page25) example schematic op-amps are used on the AIN inputs, are these necessary for the AD7794?

    Do you think my schematic is ok?

    Edit: Fixed the link and added some more.

Reply
  • Thanks for the suggestion!

    By combining the schematic of the EVAL-AD7795 and the one in the AD7713 datasheet (for the 4wire RTD on page 24) I ended up with this.

    Regarding the EVAL one, could you tell me what the 0R resistors are for? Or are they just place-holders?

    In the AD7176-2 (page25) example schematic op-amps are used on the AIN inputs, are these necessary for the AD7794?

    Do you think my schematic is ok?

    Edit: Fixed the link and added some more.

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