• State Resolved
  • Locked Locked
  • Replies 4 replies
  • Subscribers 46 subscribers
  • Views 475 views
  • Users 0 members are here
Support feedback
Options
Options
Similar topics

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

ADS1271: ADS1271B Voltage Reference Question

Mark Hughes
Intellectual 350 points
Part Number: ADS1271
Other Parts Discussed in Thread: ADS1261, ADS1260, REF6025

Hello -- I wanted to confirm that the ADS1271B will function with a VREF+ of 5.0 V VREF- of 0V, AVDD of 5.0 V and DVDD of 1.8/3.3V.

The source of confusion is that under "Electrical Characteristics" on page 4 of the datasheet (http://www.ti.com/lit/ds/symlink/ads1271.pdf

equations on page 17 appear to allow a 5V VREFP.  Additionally, the Webench reference selector recommends a 5V source.

Ultimately, I plan to connect the muRata SCA103T inclinometer (https://www.murata.com/~/media/webrenewal/products/sensor/inclinometer/sca103t/sca103t_inclinometer_datasheet__8261700a3_0.ashx?la=en-usan ADC -- so if this ADC doesn't work at a 5V VREF+ voltage, please recommend one that does.

Thanks!

Mark

  • 0
    TI__Guru 57336 points

    Hello Mark,

    Thank you for your post!

    The reference voltage used by the ADC for conversions is the differential voltage between VREFP and VREFN. This differential reference voltage (VREF) must be less than 2.65 V for both the ADS1271 and the ADS1271B.

    The equations on page 17 as well as the Electrical Characteristics table describe the conditions for the absolute voltage on the VREFP and VREFN pins.

    If you must have a 5-V reference voltage to support your sensor range, perhaps you might consider the ADS1260/ADS1261. One important difference I will point out is that this device uses a two-stage sinc filter, which will have a more limited passband response than the wideband FIR filters used in the ADS1271. Please know that the ADS1260 has yet to release, but you can sample the ADS1261 for your evaluation, if interested.

    Take a look and let me know your thoughts about its feasibility for your application.


    Best Regards,

  • 0 in reply to Ryan Andrews
    Intellectual 350 points
    Thanks Ryan,
    I appreciate the recommendations. I'll take a look at the datasheets. The sensor I'm designing for operates from a single +5V supply and provides ratiometric output in the range +0.5 to +4.5VDC. There are two sensors in the package that are arranged in an antiparallel fashion, so when one outputs 2 Volts, the other outputs 3V....etc....
    If I supply the sensor and VREF+ from the same 5V source, any supply fluctuations should theoretically cancel out. I'll read the datasheets today/tomorrow and if I have any questions I'll reopen the ticket. Thanks!
    Mark
  • 0 in reply to Mark Hughes
    TI__Guru 57336 points

    Hi Mark,

    I would caution you that the reference voltage should be a precision, low-noise input. Connecting VREFP to a 5-V supply (i.e. from an LDO) will not be as accurate and will have a direct impact on the measurement error. It would be preferable to use a precision reference IC to get the best performance out of the ADS1271. Something like the REF6025 with an integrated reference drive amplifier would work well.

    Is your sensor output single-ended or differential? If single-ended, you could connect the sensor output to the positive channel input (INP) and apply a mid-supply voltage to INN (i.e. 2.5 V). The differential measurement range would then be from -2 V to + 2 V, which is completely acceptable for VREF = 2.5 V (VREFP - VREFN). Remember that the ADC differential input range is from -VREF to +VREF. Would that work?

    Best Regards,

  • 0 in reply to Ryan Andrews
    Intellectual 350 points
    Thanks Ryan!
    That is excellent advice -- thank you for providing it. I had previously selected the LT1027LS8 as the reference -- it is a series reference that can source up to 15 mA and sink 10 mA. The sensor uses at most 5 mA (when utilizing the SPI interface, and I don't plan on using SPI). So I should theoretically be able to connect the reference directly to VREF+ and power the sensor without additional circuitry. Whether or not I do that or use an amplifier is still TBD and will likely depend on what ADC I choose.

    Unfortunately, the two single-ended outputs are capable of reaching almost the full 5V range. For example, when tilted to +30°, one output will read 4.5V and the other 0.5V, whose difference is 4V, well outside the range of this IC. I think I just misunderstood the datasheet.

    Thank you for the continued support!
    Best,
    Mark