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TPS791: Can TPS791 work as ADC Vref?

Part Number: TPS791
Other Parts Discussed in Thread: ADS7042, , LM4040

Hi team,

My customer is using AD7091R which is a ADC with internal 2.5Vref. The Vref spec. is as below picture.

However, TI doesn't have a proper ADC that has the same internal Vref. So we have to use ADS7042 which doesn't have internal Vref to compete with AD7091R and we need to use a external LDO at the ADS7042 AVDD to work as the Vref. And the cost of the external LDO needs to be less than $0.2.

In ADS7042 datasheet, it recommends TPS791 as the external LDO. But I just want to check with you if TPS791 performance is enough as the AD7091R internal Vref and if TPS791 cost can meet $0.2? Thanks.

Best regards,

Wayne

  • Hi Wayne,

    Keep in mind that there are advantages to keeping the Vref external to the ADC.
    For instance, a larger Vref will allow more resolution of the sampled voltage given an identical noise floor.

    To start, it depends on what the user is doing with the ADC.
    Do they need the ADC to act as a simple voltage monitor to give gross pass / fail criteria to a sampled voltage?
    If so, then the linear regulator accuracy would usually be sufficient.

    On the other hand, does the customer need precise Vref tolerance to make highly accurate measurements of critical voltages?
    Then a precision reference (and not a linear regulator) would be necessary.

    The TPS791 will not be as accurate across all tolerances than the precision reference inside the ADS7042, according to the datasheet specs of both components. The accuracy of linear regulators are usually worse than precision references, but precision references cannot provide the load current that linear regulators can provide. 

    If the customer only needs to power this ADC with the LDO / precision reference, then I would recommend using a precision reference if Vref tolerance is critical.  The LM4040 with the ADS7042, and a resistor might be sufficient.  Some versions of the LM4040 are under $0.2 in 1ku volumes on TI's website.  Resistors commonly sell for pennies or less in volume.  This solution may meet or exceed your requirements, if the customer does not need significant load current.  See the schematic on the first page of the LM4040 datasheet.

    If the customer needs to power multiple devices, I would look into a linear regulator solution as long as the customer can handle the increase in tolerance.
    I can direct you to another contact in our group to help with pricing, if the customer must use an LDO solution.

    Thanks,

    - Stephen

  • Hi Wayne,

    Since it has been a week without a reply, we assume that this issue has been resolved.  If this is not the case, please feel free to reply.

    Thanks,

    - Stephen