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INA125: Using multiple refrences

Julio Apps
Expert 3665 points
Part Number: INA125
Other Parts Discussed in Thread: TLV376

Hi Team,

Do you for see any issue's with using 2.5V (Pin 14) reference as the bridge bias and 1.25V (pin 13) as IAref ? Same implementation as shown on Figure 6 in the datasheet but using VrefBG for IAref instead.

  • 0
    TI__Guru* 93105 points

    Hi Julio,

    We are looking into your inquiry regarding configuring the INA125 as you are proposing. There may be input and/or output range limitations that may not make this feasible. Some additional information can help us determine if that is the case:

    • Do you intend to use a single +5 V supply?
    • What gain do you intend to establish with RG?
    • What are the input bridge characteristics, and how much input differential voltage do you expect (Vin+ - Vin-)?

    Regards, Thomas

    Precision Amplifiers Applications Engineering

  • 0 in reply to Thomas Kuehl
    TI__Expert 3665 points

    Hi Thomas,

    See my feedback below.

    • Do you intend to use a single +5 V supply? Yes
    • What gain do you intend to establish with RG? The gain resistor is 267 Ohms.
    • What are the input bridge characteristics, and how much input differential voltage do you expect (Vin+ - Vin-)? Not sure, the output expected is 0.06V - 0.148V.

  • 0 in reply to Julio Apps
    TI__Genius 10850 points

    Hi Julio,

    We took a look at this and discovered that you cannot actually tie pin 13 to IAREF. IAREF must be driven by a low-impedance source. This is explained on page 10 of the datasheet. Making this connection you proposed will degrade the gain of the internal ref amp, which in turn produces an incorrect output voltage. 

    The better way to do this would be to add a unity gain buffer between pin 13 and the IAREF pin. A precision, low-voltage TLV376 should do the trick.  

    -Tamara Alani

  • 0 in reply to Tamara M Alani
    TI__Expert 3665 points

    Tamara,

    Very much appreciate the help, we are going to go with using the 2.5V reference instead so that we may avoid using an additional component. Same as the application circuit in the datasheet.