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ADS1278-EP: Can I use I resistor divider as a voltage reference input

Xiang Maverick
Intellectual 750 points
Part Number: ADS1278-EP
Other Parts Discussed in Thread: REF5025, ADS1278, OPA2376, OPA2320, OPA2350, , INA129-EP, INA129

My analog signal is from a Wheatstone bridge supplied by 10V. I use instrument amplifier to enlarge the signal and set the common voltage as GND. The differential signal is always positive (Vp>Vn). The output of the instrument amplifier is connected to the AINP, with AINN connected to GND. I think whether can I use a resistor divider as a voltage reference input to the ADC, with the divider source by 10V? Because the bridge is supply by the same 10V. The ripple of 10V would create a common  noise both on the bridge and the reference voltage and therefore can be automatically removed. Is it better than use a reference device in this case?

  • 0
    TI__Mastermind 37570 points

    Hello Xiang,

    Yes, you can use the 10V bias source for the bridge as the reference.  You will want to divide 10V by 4, to get 2.5V as your reference.  You will also need a reference buffer, since the input of the ADS1278 will load the resistor divider.  The ADS1278EVM shows a good example of a reference buffer.  In place of the REF5025, you can use a resistor divider to convert the 10V bias to 2.5V.

    U2-A in this example is the OPA2350, but you can use a newer device with better precision, such as OPA2320 or OPA2376.

    If you are operating ADS1278 at a high data rate (f-data>10ksps) then you may also need a buffer between the output of the instrumentation amplifier and the ADC AINP input.  Many lower power instrumentation amplifiers do not have enough bandwidth to properly drive the ADC inputs at high sample rates.  Again, OPA2320 would be a good option, and possibly OPA2376.

    Regards,
    Keith Nicholas
    Precision ADC Applications

  • 0 in reply to Keith Nicholas
    Intellectual 750 points

    Thank you.

    The instrument I use is INA129-EP. The gain is set at 100. The bandwidth of the INA129-EP is listed in the following table. We can see the bandwidth is 200KHz, the max sampling rate for ADS1278-EP is 128KSPS. Do you think if ADC samples at 128KSPS. Do I need a buffer following the INA129-EP? 

  • +1 in reply to Xiang Maverick
    TI__Mastermind 37570 points

    Hello Xiang,

    Yes, if you want the ADC data rate to support the maximum 128KSPS, then you will need a buffer amplifier following the INA129.  

    Please also note; if you want to support 128KSPS, you must use the Frame-Sync serial interface described on page 31 of the datasheet.  If you only need to support a maximum data rate of 105KSPS, then you can use SPI or Frame-Sync.

    Regards,
    Keith