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ADS1256: Please check my 2.5V VREF and 5.0V circuit, Thanks.

YC Hsu
Prodigy 60 points
Part Number: ADS1256
Other Parts Discussed in Thread: OPA350, REF6025, , REF6050, TPS7A87

Here's my 2.5V VREF and 5.0V AVDD circuit base on other post , 

but I am not sure how to define these passive components. Any comments?

  • 0
    TI__Mastermind 45221 points

    Hi YC Hsu,

    Which passive components do you need help defining? It seems like all of your components are already defined. For the reference, you would just follow the datasheet recommendations

    You can also consider using the REF6025, which is a buffered version of the REF5025. This way you will not need to include the OPA350

    Also, is there any reason you are using a REF5050+buffer for the AVDD supply? Why not just use an LDO?

    -Bryan

  • 0 in reply to Bryan Lizon86
    Prodigy 60 points

    Sorry for not describe clearly :

    - Which passive components do you need help defining? 

        The 2.5V REF is refered from this post : ADS1256 - Data converters forum - Data converters - TI E2E support forums,

        I'm not sure how did he defined these value, so I want to ensure these components are placed and defined correctly.

         

    - You can also consider using the REF6025, which is a buffered version of the REF5025.

        I didn't found it has buffered version, thanks for your suggestion, here's my circuit :

        

         

    - Is there any reason you are using a REF5050+buffer for the AVDD supply? Why not just use an LDO?

        Base on the datasheet, seems that the accuracy of AVDD will effect the conversion value of ADS1256, so I want AVDD as accuracy as possible.

        What's the difference between LDO and REF5050 + buffer ?

        In other post, you have mentioned that TPS7A2050 for AVDD is recommanded, and here's my schematic : 

             

        Any Comments ?

      

  • 0 in reply to YC Hsu
    TI__Mastermind 45221 points

    Hi YC Hsu,

    I recommend following the datasheet recommendations for all of your devices. For example, it appears you have a 5MOhm resistor on the output of the REF6025. This should be more like 5mOhm

    Please refer to the datasheet for the TPS device as well. If you have specific questions about that device, please visit the Power Management E2E forum for support.

    An LDO is typically a lower cost solution, and the PSRR is typically sufficient to yield good results with our precision ADCs. Note that the ADC itself has a PSRR specification for each supply, so the ADC actually offers some rejection as well

    The TPS7A2050 has relatively high noise, so maybe consider something like the TPS7A87. This has an adjustable output, but the cost is still significantly lower compared to using REF6050+OPA, and the noise is comparable as well

    -Bryan

  • 0 in reply to Bryan Lizon86
    Prodigy 60 points

    Thanks for your replying.

    TPS7A87 seems more rely on the accuracy of resistors, though it has lower noise and higher accuracy.

    So I more prefer on fixed output type LDO.

    If I still try using TPS7A2050, will the difference be that big?

  • +1 in reply to YC Hsu
    TI__Mastermind 45221 points

    Hi YC Hsu,

    I think I was looking at the wrong datasheet yesterday, it appears the TPS7A2050 has 7uV noise while the TPS7A87 is ~4uV. So the difference is not that big, my mistake.

    Using the TPS7A2050 should be acceptable then

    -Bryan

  • 0 in reply to Bryan Lizon86
    Prodigy 60 points

    Thanks, This help me a lot.